[
{
"id": "authors:nqaej-yv378",
"collection": "authors",
"collection_id": "nqaej-yv378",
"cite_using_url": "https://authors.library.caltech.edu/records/nqaej-yv378",
"type": "book_section",
"title": "Simulation of\u00a0K-Type and\u00a0H-Type Transition Using the\u00a0Nonlinear One-Way Navier-Stokes Approach",
"book_title": "Proceedings of the 10th IUTAM Symposium on Laminar-Turbulent Transition",
"author": [
{
"family_name": "Sleeman",
"given_name": "Michael K.",
"orcid": "0000-0001-5949-9289",
"clpid": "Sleeman-Michael-K"
},
{
"family_name": "Lakebrink",
"given_name": "Matthew T."
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "In principle, transition to turbulence can be studied using direct numerical simulation (DNS) and large eddy simulation (LES), but these approaches are limited by their large computational cost. The Nonlinear One-Way Navier-Stokes (NOWNS) equations have recently been developed and applied to study the early stages of boundary layer transition, and it was demonstrated that they can accurately replicate DNS results with similar accuracy to the nonlinear parabolized stability equations (NPSE) [15]. While having greater computational cost than NPSE, NOWNS is a more robust, convergent parabolization of the governing equations and succeeds for stronger nonlinearity where NPSE fails. In this work, we use NOWNS to reproduce (to the extent possible) the H- and K-type transition scenarios simulated using DNS by Sayadi et al.
",
"doi": "10.1007/978-981-96-9829-5_19",
"issn": "1875-3507",
"isbn": "9789819698288",
"publisher": "Springer Nature Singapore",
"place_of_publication": "Singapore",
"publication_date": "2026",
"pages": "143-149"
},
{
"id": "authors:ek2h9-7xr22",
"collection": "authors",
"collection_id": "ek2h9-7xr22",
"cite_using_url": "https://authors.library.caltech.edu/records/ek2h9-7xr22",
"type": "article",
"title": "Bispectral decomposition and energy transfer in a turbulent jet",
"author": [
{
"family_name": "Nekkanti",
"given_name": "Akhil",
"orcid": "0000-0002-2173-8704",
"clpid": "Nekkanti-Akhil"
},
{
"family_name": "Pickering",
"given_name": "Ethan",
"orcid": "0000-0002-4485-6359"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The triadic interactions and nonlinear energy transfer are investigated in a subsonic turbulent jet at Re=450000. The primary focus is on the role of these interactions in the formation and attenuation of streaky structures. To this end, we employ bispectral mode decomposition, a technique that extracts coherent structures associated with dominant triadic interactions. A strong triadic correlation is identified between Kelvin–Helmholtz (KH) wavepackets and streaks: interactions between counter-rotating KH waves generates streamwise vortices, which subsequently give rise to streaks through the lift-up mechanism. The most energetic streaks occur at azimuthal wavenumber m=2, with the dominant contributing triad being [m1,m2,m3]=[1,1,2]. The spectral energy budget reveals that the net effect of nonlinear triadic interactions is an energy loss from the streaks. As these streaks convect downstream, they engage in further nonlinear interactions with other frequencies, which drain their energy and ultimately lead to their attenuation. Further analysis identifies the dominant scales and direction of energy transfer across different spatial regions of the jet. While the turbulent jet exhibits a forward energy cascade in a global sense, the direction of energy transfer varies locally: in the shear layer near the nozzle exit, triadic interactions among smaller scales dominate, resulting in an inverse energy cascade, whereas farther downstream, beyond the end of the potential core, interactions among larger scales prevail, leading to a forward cascade.
",
"doi": "10.1017/jfm.2025.10922",
"issn": "0022-1120",
"publisher": "Cambridge University Press (CUP)",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2025-12-25",
"volume": "1025",
"pages": "A35"
},
{
"id": "authors:xb59b-w5p02",
"collection": "authors",
"collection_id": "xb59b-w5p02",
"cite_using_url": "https://authors.library.caltech.edu/records/xb59b-w5p02",
"type": "article",
"title": "Instabilities in the flow over a spinning disk at angle of attack",
"author": [
{
"family_name": "Lee",
"given_name": "Marcus Kuok Kuan",
"orcid": "0000-0003-3972-843X",
"clpid": "Lee-Marcus"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "McKeon",
"given_name": "Beverley J.",
"orcid": "0000-0003-4220-1583",
"clpid": "McKeon-B-J"
}
],
"abstract": "Three-dimensional laminar flow over an inclined spinning disk is investigated at a Reynolds number of Re = 500 and an angle of attack of α = 25°, for tip-speed ratios up to 3. Numerical simulations are performed to investigate the effect of spin on the aerodynamics and characterise the instabilities that occur. Increasing tip-speed ratio significantly increases both lift and drag monotonically. Several distinct wake regimes are observed, including vortex shedding in the non-spinning case, vortex-shedding suppression at moderate tip-speed ratios and a distinct corkscrew-like short-wavelength instability in the advancing tip vortex at higher tip-speed ratios. Vorticity generated by the spinning disk strengthens the advancing tip vortex, inducing a spanwise stretching in the trailing-edge vortex sheet. This helps to dissipate the vorticity, which in turn prevents roll up and suppresses vortex shedding. The short-wavelength instability shows qualitative and quantitative matches to the (-2,0,1) principal mode of the elliptic instabilities seen in pairs of counter-rotating Batchelor vortices. The addition of vorticity from the disk rotation significantly alters the circulation and axial velocity in the tip vortices, giving rise to elliptic instability despite its absence in the non-spinning case. In select cases, lock-in between the frequency of the elliptic instability and twice the spin frequency is observed, indicating that disk rotation acts as an additional forcing for the elliptic instability. Additional simulations at different Reynolds numbers and angle of attacks are considered to examine the robustness of observed phenomena across different parameter combinations.
",
"doi": "10.1017/jfm.2025.10943",
"issn": "0022-1120",
"publisher": "Cambridge University Press (CUP)",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2025-12-25",
"volume": "1025",
"pages": "A48"
},
{
"id": "authors:q2err-6nh23",
"collection": "authors",
"collection_id": "q2err-6nh23",
"cite_using_url": "https://authors.library.caltech.edu/records/q2err-6nh23",
"type": "article",
"title": "Spectral proper orthogonal decomposition of rapid snapshot pairs sampled at sub-Nyquist intervals",
"author": [
{
"family_name": "Cardinale",
"given_name": "Caroline",
"orcid": "0009-0007-6446-7047",
"clpid": "Cardinale-Caroline"
},
{
"family_name": "Brunton",
"given_name": "Steven L."
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Modal decomposition methods are important for characterizing the low-dimensional dynamics of complex systems, including turbulent flows. Different methods have varying data requirements and produce modes with different properties. Spectral proper orthogonal decomposition (SPOD) produces orthogonal, energy-ranked spatial modes at discrete temporal frequencies for statistically stationary flows. However, SPOD requires long stretches of sequential, uniformly sampled, time-resolved data. These data requirements limit SPOD's use in experimental settings where the maximum capture rate of a camera is often slower than the Nyquist sampling rate required to resolve the highest turbulent frequencies. However, if two particle image velocimetry systems operate in tandem, pairs of data can be acquired that are arbitrarily close in time. The dynamic mode decomposition (DMD) uses this pairwise data to resolve frequencies up to the Nyquist frequency associated with the small time step within a pair. However, these modes do not form a basis and have no set ranking. The present work attempts to compute SPOD modes from pairwise data with a small time step but with large gaps between pairs. We use DMD on pairwise data to estimate segmentwise, uniformly sampled series that can then be used to estimate the SPOD modes, intending to resolve frequencies between the gap and pair Nyquist limits. The method is tested on numerically obtained data of the linearized complex Ginzburg-Landau equation, as well as a Mach 0.4 isothermal turbulent jet. For the jet, pairwise SPOD can accurately dealias the SPOD spectrum and estimate mode shapes at frequencies up to St≈1.0 while using more than 90% fewer data.
",
"doi": "10.1103/vxqz-8fl5",
"issn": "2469-990X",
"publisher": "American Physical Society",
"publication": "Physical Review Fluids",
"publication_date": "2025-12-24",
"series_number": "12",
"volume": "10",
"issue": "12",
"pages": "124904"
},
{
"id": "authors:58y0k-71223",
"collection": "authors",
"collection_id": "58y0k-71223",
"cite_using_url": "https://authors.library.caltech.edu/records/58y0k-71223",
"type": "article",
"title": "Normality-based analysis of multiscale velocity gradients and energy transfer in direct and large-eddy simulations of isotropic turbulence",
"author": [
{
"family_name": "Arun",
"given_name": "Rahul",
"orcid": "0000-0002-5942-169X",
"clpid": "Arun-Rahul"
},
{
"family_name": "Kamal",
"given_name": "Mostafa",
"orcid": "0009-0000-3892-4987"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Johnson",
"given_name": "Perry L.",
"orcid": "0000-0002-7929-9396"
}
],
"abstract": "Symmetry-based analyses of multiscale velocity gradients highlight that strain self-amplification (SS) and vortex stretching (VS) drive forward energy transfer in turbulent flows. By contrast, a strain–vorticity covariance mechanism produces backscatter that contributes to the bottleneck effect in the subinertial range of the energy cascade. We extend these analyses by using a normality-based decomposition of filtered velocity gradients in forced isotropic turbulence to distinguish contributions from normal straining, pure shearing and rigid rotation at a given scale. Our analysis of direct numerical simulation (DNS) data illuminates the importance of shear layers in the inertial range and (especially) the subinertial range of the cascade. Shear layers contribute significantly to SS and VS and play a dominant role in the backscatter mechanism responsible for the bottleneck effect. Our concurrent analysis of large-eddy simulation (LES) data characterizes how different closure models affect the flow structure and energy transfer throughout the resolved scales. We thoroughly demonstrate that the multiscale flow features produced by a mixed model closely resemble those in a filtered DNS, whereas the features produced by an eddy viscosity model resemble those in an unfiltered DNS at a lower Reynolds number. This analysis helps explain how small-scale shear layers, whose imprint is mitigated upon filtering, amplify the artificial bottleneck effect produced by the eddy viscosity model in the inertial range of the cascade. Altogether, the present results provide a refined interpretation of the flow structures and mechanisms underlying the energy cascade and insight for designing and evaluating LES closure models.
",
"doi": "10.1017/jfm.2025.10748",
"issn": "0022-1120",
"publisher": "Cambridge University Press (CUP)",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2025-10-25",
"volume": "1021",
"pages": "A47"
},
{
"id": "authors:18py7-q1531",
"collection": "authors",
"collection_id": "18py7-q1531",
"cite_using_url": "https://authors.library.caltech.edu/records/18py7-q1531",
"type": "article",
"title": "Numerical methods for multiphase flows",
"author": [
{
"family_name": "Garcia-Villalba",
"given_name": "Manuel",
"orcid": "0000-0002-6953-2270"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Desjardins",
"given_name": "Olivier",
"orcid": "0000-0001-6477-6658"
},
{
"family_name": "Lucas",
"given_name": "Dirk",
"orcid": "0000-0003-0463-2278"
},
{
"family_name": "Mani",
"given_name": "Ali"
},
{
"family_name": "Marchisio",
"given_name": "Daniele",
"orcid": "0000-0002-9104-0571"
},
{
"family_name": "Matar",
"given_name": "Omar K.",
"orcid": "0000-0002-0530-8317"
},
{
"family_name": "Picano",
"given_name": "Francesco",
"orcid": "0000-0002-3943-8187"
},
{
"family_name": "Zaleski",
"given_name": "St\u00e9phane",
"orcid": "0000-0003-2004-9090"
}
],
"abstract": "\n
\n
Multiphase flows are ubiquitous in both nature and engineering. Over the past two to three decades, substantial progress has been made in developing numerical methods for simulating these complex flows. Yet, significant challenges persist in accurately capturing intricate interfacial dynamics and the multi-scale interactions inherent to multiphase systems. This review focuses on several key numerical approaches that have proven particularly relevant from both practical and theoretical perspectives. In particular, we discuss Volume-Of-Fluid techniques, level set methods, diffuse interface models, and front tracking methods, along with immersed boundary strategies designed for particle-laden flows. We also examine multi-fluid Eulerian frameworks, population balance models for reactive processes, and sub-grid scale techniques for handling unresolved dynamics. Furthermore, emerging hybrid strategies that integrate conventional numerical methods with data-driven machine learning techniques are highlighted as promising directions. In conclusion, while current methodologies offer valuable insights into multiphase flow behavior, continued interdisciplinary efforts are essential to enhance predictive accuracy, computational efficiency, and the overall applicability of these simulations to real-world challenges.
\n
\n
In this paper, we present resolvent4py, a parallel Python package for the analysis, model reduction and control of large-scale linear systems with millions or billions of degrees of freedom. This package provides the user with a friendly Python-like experience (akin to that of well-established libraries such as numpy and scipy), while enabling MPI-based parallelism through mpi4py, petsc4py and slepc4py. In turn, this allows for the development of streamlined and efficient Python code that can be used to solve several problems in fluid mechanics, solid mechanics, graph theory, molecular dynamics and several other fields.
",
"doi": "10.1016/j.softx.2025.102286",
"issn": "2352-7110",
"publisher": "Elsevier",
"publication": "SoftwareX",
"publication_date": "2025-09",
"volume": "31",
"pages": "102286"
},
{
"id": "authors:jsmfb-ecf46",
"collection": "authors",
"collection_id": "jsmfb-ecf46",
"cite_using_url": "https://authors.library.caltech.edu/records/jsmfb-ecf46",
"type": "article",
"title": "Boundary-Layer Stability Analysis Using the Nonlinear One-Way Navier\u2013Stokes Approach",
"author": [
{
"family_name": "Sleeman",
"given_name": "Michael K.",
"orcid": "0000-0001-5949-9289",
"clpid": "Sleeman-Michael-K"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lakebrink",
"given_name": "Matthew T."
}
],
"abstract": "We extend the one-way Navier Stokes (OWNS) approach to support nonlinear interactions between waves of different frequencies, which will enable nonlinear analysis of instability and transition. In OWNS, the linearized Navier\u2013Stokes equations are parabolized and solved in the frequency domain as a spatial initial-value (marching) problem. OWNS yields a reduced computational cost compared to global solvers while also conferring numerous advantages over the parabolized stability equations (PSEs), despite its higher computational cost relative to PSE, that we seek to extend to nonlinear analysis. We validate the nonlinear OWNS (NOWNS) method by examining the nonlinear evolution of two- and three-dimensional disturbances in a low-speed Blasius boundary layer compared to nonlinear PSE (NPSE) and direct numerical simulation (DNS) results from the literature. We demonstrate that NOWNS can be used to simulate flows involving blowing/suction strips, is more robust to numerical noise, and converges for stronger nonlinearities, as compared to NPSE.",
"doi": "10.2514/1.j064909",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2025-08",
"series_number": "8",
"volume": "63",
"issue": "8",
"pages": "3145\u20133159"
},
{
"id": "authors:99b3c-1bd71",
"collection": "authors",
"collection_id": "99b3c-1bd71",
"cite_using_url": "https://authors.library.caltech.edu/records/99b3c-1bd71",
"type": "article",
"title": "Linear Analysis of Boundary-Layer Instabilities on a Finned Cone at Mach 6",
"author": [
{
"family_name": "Araya",
"given_name": "Daniel B.",
"orcid": "0000-0001-6833-6852"
},
{
"family_name": "Bitter",
"given_name": "Neal P."
},
{
"family_name": "Wheaton",
"given_name": "Bradley M.",
"orcid": "0009-0005-5765-0316"
},
{
"family_name": "Kamal",
"given_name": "Omar",
"orcid": "0000-0002-3431-2964",
"clpid": "Kamal-Omar"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Knutson",
"given_name": "Anthony"
},
{
"family_name": "Johnson",
"given_name": "Heath"
},
{
"family_name": "Nichols",
"given_name": "Joseph"
},
{
"family_name": "Candler",
"given_name": "Graham V."
},
{
"family_name": "Russo",
"given_name": "Vincenzo"
},
{
"family_name": "Brehm",
"given_name": "Christoph",
"orcid": "0000-0002-9006-3587"
}
],
"abstract": "Boundary-layer instabilities for a finned cone at Mach=6, \ud835\udc45\u2062\ud835\udc52=8.4×106 [m−1], and zero incidence angle are examined using linear stability methods of varying fidelity and maturity. The geometry and laminar flow conditions correspond to experiments conducted at the Boeing Air Force Mach 6 Quiet Tunnel at Purdue University. Where possible, a common baseflow is utilized among the stability computations, and comparisons are made along the acreage of the cone where transition is first observed in the experiment. Stability results utilizing linear stability theory, planar parabolized stability equations, one-way Navier–Stokes, forced direct numerical simulation, and adaptive mesh refinement wavepacket tracking are presented. A dominant three-dimensional vortex instability occurring at ≈250 kHz is identified and correlates well with experimental measurements of transition onset. With the exception of linear stability theory, all of the higher-fidelity linear methods considered in this work were consistent in predicting the initial growth and general structure of the vortex instability as it evolved downstream. Some of the challenges, opportunities, and development needs of the stability methods considered are discussed.
",
"doi": "10.2514/1.j064036",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2025-07",
"series_number": "7",
"volume": "63",
"issue": "7",
"pages": "2594-2614"
},
{
"id": "authors:tab55-87k30",
"collection": "authors",
"collection_id": "tab55-87k30",
"cite_using_url": "https://authors.library.caltech.edu/records/tab55-87k30",
"type": "article",
"title": "Fast and Robust Method for Screened Poisson Lattice Green's Function Using Asymptotic Expansion and Fast Fourier Transform",
"author": [
{
"family_name": "Hou",
"given_name": "Wei",
"orcid": "0000-0001-8023-6395",
"clpid": "Hou-Wei"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We study the lattice Green’s function (LGF) of the screened Poisson equation on a two-dimensional rectangular lattice. This LGF arises in numerical analysis, random walks, solid-state physics, and other fields. Its defining characteristic is the screening term, which defines different regimes. When its coefficient is large, we can accurately approximate the LGF with an exponentially converging asymptotic expansion, and its convergence rate monotonically increases with the coefficient of the screening term. To tabulate the LGF when the coefficient is not large, we derive a one-dimensional integral representation of the LGF. We show that the trapezoidal rule can approximate this integral with exponential convergence, and we propose an efficient algorithm for its evaluation via the fast Fourier transform. We discuss applications including computing the LGF of the three-dimensional Poisson equation with one periodic direction and the return probability of a two-dimensional random walk with killing.
",
"doi": "10.1137/24m1646789",
"issn": "1064-8275",
"publisher": "Society for Industrial & Applied Mathematics (SIAM)",
"publication": "SIAM Journal on Scientific Computing",
"publication_date": "2025-04",
"series_number": "2",
"volume": "47",
"issue": "2",
"pages": "A1198-A1224"
},
{
"id": "authors:p8shq-rj740",
"collection": "authors",
"collection_id": "p8shq-rj740",
"cite_using_url": "https://authors.library.caltech.edu/records/p8shq-rj740",
"type": "article",
"title": "An adaptive lattice Green's function method for external flows with two unbounded and one homogeneous directions",
"author": [
{
"family_name": "Hou",
"given_name": "Wei",
"orcid": "0000-0001-8023-6395",
"clpid": "Hou-Wei"
},
{
"family_name": "Colonius",
"given_name": "Timothy E.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We solve the incompressible Navier-Stokes equations using a lattice Green's function (LGF) approach, including immersed boundaries (IB) and adaptive mesh refinement (AMR), for external flows with one homogeneous direction (e.g. infinite cylinders of arbitrary cross-section). We hybridize a Fourier collocation (pseudo-spectral) method for the homogeneous direction with a specially designed, staggered-grid finite-volume scheme on an AMR grid. The Fourier series is also truncated variably according to the refinement level in the other directions. We derive new algorithms to tabulate the LGF of the screened Poisson operator and viscous integrating factor. After adapting other algorithmic details from the fully inhomogeneous case [1], we validate and demonstrate the new method with transitional and turbulent flows over a circular cylinder at Re=300 and Re=12,000, respectively.
",
"doi": "10.1016/j.jcp.2024.113370",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2024-12-15",
"volume": "519",
"pages": "113370"
},
{
"id": "authors:vgb5s-pqs25",
"collection": "authors",
"collection_id": "vgb5s-pqs25",
"cite_using_url": "https://authors.library.caltech.edu/records/vgb5s-pqs25",
"type": "article",
"title": "Velocity gradient partitioning in turbulent flows",
"author": [
{
"family_name": "Arun",
"given_name": "Rahul",
"orcid": "0000-0002-5942-169X",
"clpid": "Arun-Rahul"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The velocity gradient tensor can be decomposed into normal straining, pure shearing and rigid rotation tensors, each with distinct symmetry and normality properties. We partition the strength of turbulent velocity gradients based on the relative contributions of these constituents in several canonical flows. These flows include forced isotropic turbulence, turbulent channels and turbulent boundary layers. For forced isotropic turbulence, the partitioning is in excellent agreement with previous results. For wall-bounded turbulence, the partitioning collapses onto the isotropic partitioning far from the wall, where the mean shearing is relatively weak. By contrast, the near-wall partitioning is dominated by shearing. Between these two regimes, the partitioning collapses well at sufficiently high friction Reynolds numbers and its variations in the buffer layer and the log-law region can be reasonably modelled as a function of the mean shearing strength. Altogether, our results highlight the expressivity and broad applicability of the velocity gradient partitioning as advantages for turbulence modelling.",
"doi": "10.1017/jfm.2024.1021",
"issn": "0022-1120",
"publisher": "Cambridge University Press (CUP)",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2024-12-10",
"volume": "1000",
"pages": "R5"
},
{
"id": "authors:qbwkc-xt420",
"collection": "authors",
"collection_id": "qbwkc-xt420",
"cite_using_url": "https://authors.library.caltech.edu/records/qbwkc-xt420",
"type": "article",
"title": "Superresolution and analysis of three-dimensional velocity fields of underexpanded jets in different screech modes",
"author": [
{
"family_name": "Lee",
"given_name": "Chungil",
"orcid": "0000-0002-3629-427X"
},
{
"family_name": "Ozawa",
"given_name": "Yuta",
"orcid": "0000-0002-5895-0506"
},
{
"family_name": "Nagata",
"given_name": "Takayuki",
"orcid": "0000-0003-3644-4888"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Nonomura",
"given_name": "Taku",
"orcid": "0000-0001-7739-7104"
}
],
"abstract": "Time-resolved (TR), three-dimensional (3D) velocity fields of screeching, underexpanded jets are estimated using non-time-resolved particle image velocimetry and simultaneous TR microphone measurements. Specifically, we aim to reconstruct TR 3D velocity fluctuation fields associated with the A2, B, and C modes of a screeching jet using a linear regression model and to analyze screech dynamics of these modes. The linear regression model is constructed on the basis of a linear relationship between the velocity and acoustic fields. Three nozzle pressure ratios (NPRs) of 2.30, 2.97, and 3.40 are employed. The dominant azimuthal modes for three cases are investigated using azimuthal Fourier coefficients of the acoustic data obtained by the azimuthal array of eight microphones placed near the nozzle exit. The dominant azimuthal modes at NPRs of 2.30, 2.97, and 3.40 are m=0, 1, and 1, respectively. The first two proper orthogonal decomposition (POD) modes in these azimuthal modes are dominant at all NPRs and are associated with screech. 3D velocity fluctuation fields associated with screech are reconstructed from these leading POD modes of the acoustic data. The reconstructed 3D velocity fluctuation fields at NPRs of 2.97 and 3.40 exhibit two helical structures with opposite rotation directions. The present results demonstrate that, in the B mode, the flapping structure exhibits random clockwise and counterclockwise rotations over an extended time domain, while maintaining a consistent direction within short time domains. In addition, in the C mode, two helical structures with opposite rotation directions, as well as the flapping structure, are observed.
",
"doi": "10.1103/physrevfluids.9.104604",
"issn": "2469-990X",
"publisher": "American Physical Society",
"publication": "Physical Review Fluids",
"publication_date": "2024-10-18",
"series_number": "10",
"volume": "9",
"issue": "10",
"pages": "104604"
},
{
"id": "authors:yhrx9-xg748",
"collection": "authors",
"collection_id": "yhrx9-xg748",
"cite_using_url": "https://authors.library.caltech.edu/records/yhrx9-xg748",
"type": "article",
"title": "Method for scalable and performant GPU-accelerated simulation of multiphase compressible flow",
"author": [
{
"family_name": "Radhakrishnan",
"given_name": "Anand",
"clpid": "Radhakrishnan-Anand"
},
{
"family_name": "Le Berre",
"given_name": "Henry",
"orcid": "0000-0002-4781-9502",
"clpid": "Le-Berre-Henry"
},
{
"family_name": "Wilfong",
"given_name": "Benjamin",
"clpid": "Wilfong-Benjamin"
},
{
"family_name": "Spratt",
"given_name": "Jean-Sebastien",
"orcid": "0000-0002-1962-4214",
"clpid": "Spratt-Jean-Sebastien"
},
{
"family_name": "Rodriguez",
"given_name": "Mauro",
"orcid": "0000-0003-0545-0265",
"clpid": "Rodriguez-Mauro"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-Spencer-H"
}
],
"abstract": "Multiphase compressible flows are often characterized by a broad range of space and time scales, entailing large grids and small time steps. Simulations of these flows on CPU-based clusters can thus take several wall-clock days. Offloading the compute kernels to GPUs appears attractive but is memory-bound for many finite-volume and -difference methods, damping speedups. Even when realized, GPU-based kernels lead to more intrusive communication and I/O times owing to lower computation costs. We present a strategy for GPU acceleration of multiphase compressible flow solvers that addresses these challenges and obtains large speedups at scale. We use OpenACC for directive-based offloading of all compute kernels while maintaining low-level control when needed. An established Fortran preprocessor and metaprogramming tool, Fypp, enables otherwise hidden compile-time optimizations. This strategy exposes compile-time optimizations and high memory reuse while retaining readable, maintainable, and compact code. Remote direct memory access realized via CUDA-aware MPI and GPUDirect reduces halo-exchange communication time. We implement this approach in the open-source solver MFC [1]. Metaprogramming results in an 8-times speedup of the most expensive kernels compared to a statically compiled program, reaching 46% of peak FLOPs on modern NVIDIA GPUs and high arithmetic intensity (about 10 FLOPs/byte). In representative simulations, a single NVIDIA A100 GPU is 7-times faster compared to an Intel Xeon Cascade Lake (6248) CPU die, or about 300-times faster compared to a single such CPU core. At the same time, near-ideal (97%) weak scaling is observed for at least 13824 GPUs on OLCF Summit. A strong scaling efficiency of 84% is retained for an 8-times increase in GPU count. Collective I/O, implemented via MPI3, helps ensure the negligible contribution of data transfers (<1% of the wall time for a typical, large simulation). Large many-GPU simulations of compressible (solid-)liquid-gas flows demonstrate the practical utility of this strategy.
",
"doi": "10.1016/j.cpc.2024.109238",
"issn": "0010-4655",
"publisher": "Elsevier",
"publication": "Computer Physics Communications",
"publication_date": "2024-09",
"volume": "302",
"pages": "109238"
},
{
"id": "authors:y2z8a-sr065",
"collection": "authors",
"collection_id": "y2z8a-sr065",
"cite_using_url": "https://authors.library.caltech.edu/records/y2z8a-sr065",
"type": "conference_item",
"title": "A phase change model for the simulation of cavitating droplet aerobreakup using interface-capturing schemes",
"author": [
{
"family_name": "Chreim",
"given_name": "Jose Rodolfo",
"orcid": "0000-0002-2809-9116",
"clpid": "Chreim-Jose-Rodolfo"
},
{
"family_name": "Rodriguez",
"given_name": "Mauro, Jr.",
"orcid": "0000-0003-0545-0265",
"clpid": "Rodriguez-Mauro-Jr"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Interface-capturing schemes are well established for multi-component, immiscible flows, but
simulating phase changing flows is yet a challenge. For an N-component system including reacting
liquid and vapor states of one of the materials, we adopt the so-called six-equation model with source
terms that account for mechanical, thermal, and chemical disequilibrium furnished with an infinitely
fast relaxation procedure [1]. We solve the governing equations with our validated, GPU-enabled,
open-source, high-order-accurate flow solver called MFC [2], in which the relaxation process towards
equilibrium is simplified, for fluids obeying the stiffened gas equation of state, to finding the roots of
a 2 × 2 system of nonlinear equations.
\n
Numerical experiments have been performed for a variety of test cases, and agreed well with previous
work [1], but there are still challenging simulations of interest in academia and industry, such as
single bubble dynamics and aero-droplet breakup problems in which phase change plays an important
role. For the latter, recent literature has shown that, when subject to a sufficiently strong shock,
internally reflected rarefaction waves can focus and induce cavitation [3]. We managed to reproduce
this behavior, generating vapor at the focal point, but the results are yet preliminary and better criteria
for both triggering the model and sustaining the newly generated mixture region must be established,
since the results depend on the sensibility of the current criteria. Additionally, phase change was
observed at locations that are known not to happen.
\n
Therefore, in this presentation we intend to discuss modifications to our model so it can capture and
sustain phase change at the expected locations, in accordance with both theoretical and experimental
observations. We will focus on presenting results for droplet aerobreakup problems with induced
cavitation.
",
"doi": "10.7907/y2z8a-sr065",
"publisher": "California Institute of Technology",
"publication_date": "2024-06-05"
},
{
"id": "authors:w1hg5-p4454",
"collection": "authors",
"collection_id": "w1hg5-p4454",
"cite_using_url": "https://authors.library.caltech.edu/records/w1hg5-p4454",
"type": "conference_item",
"title": "Localized Resolvent-Mode Bases for Turbulence Statistics",
"book_title": "30th AIAA/CEAS Aeroacoustics Conference (2024)",
"author": [
{
"family_name": "Eichberger",
"given_name": "Ethan R.",
"clpid": "Eichberger-Ethan-R"
},
{
"family_name": "Heidt",
"given_name": "Liam",
"orcid": "0000-0003-1967-6847",
"clpid": "Heidt-Liam"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Modes from global resolvent analyses have been shown to accurately model the frequencies and spatial structure of the dominant coherent structures in several turbulent flows. However, resolvent-mode forcing models must be developed to predict the amplitude of the structures or other flow statistics, including the radiated noise. The present research aims to apply data-driven approaches to learn forcing coefficients from lower-order statistics available from Reynolds-averaged Navier-Stokes (RANS) predictions. As a first step towards this goal, we present a novel localized resolvent framework that reconstructs global quantities at low rank through spatially restricting the resolvent forcing and response domains. To illustrate the flexibility and robustness of the proposed framework, we initially utilize localized resolvent modes to reconstruct the spectral proper orthogonal decomposition (SPOD) modes of an isothermal Mach 0.4 jet at \ud835\udc79\ud835\udc86 = 450, 000 = 450, 000. The results showcase the flexibility localized resolvent modes provide in the construction of global SPOD, while using 10 or fewer total localized modes total across \ud835\udc7a\ud835\udc95 = [0.05, 1.00]. Furthermore, we employ localized resolvent modes to reconstruct second-order statistics, comparing their performance with that of global modes. At low reconstruction error, it is shown that about twice as many global modes are needed to achieve comparable errors.
",
"doi": "10.2514/6.2024-3205",
"isbn": "9781624107207",
"publisher": "AIAA",
"place_of_publication": "Rome, Italy",
"publication_date": "2024-06-04"
},
{
"id": "authors:wsbme-be636",
"collection": "authors",
"collection_id": "wsbme-be636",
"cite_using_url": "https://authors.library.caltech.edu/records/wsbme-be636",
"type": "conference_item",
"title": "Resolvent Modeling of Subsonic Jet Noise",
"book_title": "30th AIAA/CEAS Aeroacoustics Conference (2024)",
"author": [
{
"family_name": "Hasparyk",
"given_name": "Barbara"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587"
},
{
"family_name": "Lesshafft",
"given_name": "Lutz",
"orcid": "0000-0002-2513-4553"
},
{
"family_name": "Pickering",
"given_name": "Ethan",
"orcid": "0000-0002-4485-6359"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "When the jet noise is cast in the form of a linear input-output problem, the cross-spectral-density (CSD) matrix of the sound field is forced by the CSD of non-linear interactions via the resolvent operator. The forcing CSD is difficult to compute or measure, but its projection onto the resolvent input space can be identified from the CSD of the sound field. In a recent study using data from numerical simulation, such an identification showed that a low-rank truncation of the forcing-projection matrix can be used to reconstruct the acoustic field of transonic and supersonic turbulent jets with Mach numbers 0.9 and 1.5 respectively. Encouraged by this result, we performed two-point acoustic measurements in isothermal turbulent jets over a broad range of subsonic Mach numbers. In the present work, these CSD matrices are used to obtain an empirical model of the forcing-projection matrix, following the procedure reported in Pickering et al., 2021. We investigate the parametric dependence of the low-rank, forcing-projection matrix on Mach number, frequency, and azimuthal mode, and we propose a model that captures this dependence and, allowing computation of downstream radiation with 1.5dB precision for subsonic jets in the Mach-number range 0.7 to 0.9.
",
"doi": "10.2514/6.2024-3199",
"isbn": "9781624107207",
"publisher": "AIAA",
"place_of_publication": "Rome, Italy",
"publication_date": "2024-06-04"
},
{
"id": "authors:tgmk3-sgs53",
"collection": "authors",
"collection_id": "tgmk3-sgs53",
"cite_using_url": "https://authors.library.caltech.edu/records/tgmk3-sgs53",
"type": "conference_item",
"title": "Nonlinear Interactions in Non-Resonant, Homogeneous Turbulent Jets",
"book_title": "30th AIAA/CEAS Aeroacoustics Conference (2024)",
"author": [
{
"family_name": "Nekkanti",
"given_name": "Akhil",
"orcid": "0000-0002-2173-8704",
"clpid": "Nekkanti-Akhil"
},
{
"family_name": "Pickering",
"given_name": "Ethan",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-Ethan-Marcus"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235"
}
],
"abstract": "Bispectral mode decomposition is used to investigate triadic interactions within a Mach 0.4 turbulent jet. We explore its potential to identify dominant triadic interactions and their associated spatial structures in an unforced turbulent jet. The bispectral measure is broadband in frequency for each azimuthal wavenumber triad. The [1,1,2] and [0,0,0] azimuthal wavenumber triads are dominant, emphasizing the importance of the self-interactions of the helical and axisymmetric components. Bispectral modes reveal that streaky structures are fed by the interaction of a Kelvin-Helmholtz wavepacket with its conjugate. Streaks are also observed in other frequency interactions, occurring in regions where the structures of these frequencies are spatially active. Furthermore, integral interaction maps and nonlinear transfer terms are computed to determine the direction of energy transfer and to pinpoint the spatial regions where nonlinearity is most active. As the shear layer develops, small scales interact nonlinearly, transferring energy to larger scales. Moving downstream, near the potential core closure, larger scales become more active, resulting in a forward energy cascade.
",
"doi": "10.2514/6.2024-3414",
"isbn": "9781624107207",
"publisher": "AIAA",
"place_of_publication": "Rome, Italy",
"publication_date": "2024-06-04"
},
{
"id": "authors:1jzsb-2s708",
"collection": "authors",
"collection_id": "1jzsb-2s708",
"cite_using_url": "https://authors.library.caltech.edu/records/1jzsb-2s708",
"type": "conference_item",
"title": "Coherence Decay in Turbulent Jets by Stochastic Modelling Under Location Uncertanty",
"book_title": "30th AIAA/CEAS Aeroacoustics Conference (2024)",
"author": [
{
"family_name": "Tissot",
"given_name": "Gilles",
"orcid": "0000-0001-7433-5637",
"clpid": "Tissot-Gilles"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-Andr\u00e9"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-Peter"
},
{
"family_name": "M\u00e9min",
"given_name": "Etienne",
"orcid": "0000-0003-2307-5438",
"clpid": "M\u00e9min-Etienne"
}
],
"abstract": "\n
\n
Coherence decay has been understood to be a key quantity to predict acoustic noise emitted by wavepackets in subsonic turbulent jets. Frequency-domain frameworks such as input-output and resolvent analyses are able to predict accurately the spatial structure of wavepackets turbulent flows compared to coherent structures educed from simulation data (as for example identified using spectral proper orthogonal, SPOD). However, at least at reduced-order, they are unable to capture two-point statistics such as coherence. A missing piece is the modelling of variability induced by the turbulence, which jitters (disorganises) the coherent structures and leads to stronger noise radiation. The aim of the present study is to consider the impact of turbulence on jet wavepackets through stochastic modelling under location uncertainty. This framework considers the conservation of mass and momentum of fluid parcels submitted to a stochastic transport, representing here the effect of turbulence. By linearising the resulting generalised stochastic Navier-Stokes equations and expressing it in the Fourier domain, a stochastic linear model (SLM) is obtained. We explore in this paper that ability of SLM to predict the two point coherence of the wavepackets in turbulent jets, and show its impact on acoustic emissions.
\n
\n
We consider the problem of filtering dynamical systems, possibly stochastic, using observations of statistics. Thus, the computational task is to estimate a time-evolving density ρ(v,t) given noisy observations of the true density ρ†; this contrasts with the standard filtering problem based on observations of the state v. The task is naturally formulated as an infinite-dimensional filtering problem in the space of densities ρ. However, for the purposes of tractability, we seek algorithms in state space; specifically, we introduce a mean-field state-space model, and using interacting particle system approximations to this model, we propose an ensemble method. We refer to the resulting methodology as the ensemble Fokker–Planck filter (EnFPF). Under certain restrictive assumptions, we show that the EnFPF approximates the Kalman–Bucy filter for the Fokker–Planck equation, which is the exact solution to the infinite-dimensional filtering problem. Furthermore, our numerical experiments show that the methodology is useful beyond this restrictive setting. Specifically, the experiments show that the EnFPF is able to correct ensemble statistics, to accelerate convergence to the invariant density for autonomous systems, and to accelerate convergence to time-dependent invariant densities for non-autonomous systems. We discuss possible applications of the EnFPF to climate ensembles and to turbulence modeling.
",
"doi": "10.1063/5.0171827",
"issn": "1054-1500",
"publisher": "American Institute of Physics",
"publication": "Chaos: An Interdisciplinary Journal of Nonlinear Science",
"publication_date": "2024-03",
"series_number": "3",
"volume": "34",
"issue": "3",
"pages": "033119"
},
{
"id": "authors:g851r-ap902",
"collection": "authors",
"collection_id": "g851r-ap902",
"cite_using_url": "https://authors.library.caltech.edu/records/g851r-ap902",
"type": "conference_item",
"title": "Two-point measurements on the acoustic field of subsonic turbulent jets",
"book_title": "AIAA AVIATION 2023 Forum",
"author": [
{
"family_name": "Gramiscelli Hasparyk",
"given_name": "Barbara",
"clpid": "Gramiscelli-Hasparyk-Barbara"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-Peter"
},
{
"family_name": "Lebedev",
"given_name": "Anton",
"clpid": "Lebedev-Anton"
},
{
"family_name": "Lesshafft",
"given_name": "Lutz",
"orcid": "0000-0002-2513-4553",
"clpid": "Lesshafft-Lutz"
},
{
"family_name": "Pickering",
"given_name": "Ethan M.",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-Ethan-M"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "\n
\n
Two-point acoustic measurements are made for subsonic, isothermal turbulent jets over a range of Mach numbers, spanning from 0.4 to 0.9. The measurements are made using two antennae, each with 18 azimuthally distributed microphones, that can be independently displaced in the streamwise direction. The measurement system is used to construct CSD matrices of the sound field for each Mach number. We report a detailed analysis of the two-point structure of the sound field, which is decomposed using a Fourier series in azimuth, Fourier transform in time, and Spectral Proper Orthogonal Decomposition in the inhomogeneous streamwise direction. Analysed in this way, Mach- and Strouhal-number dependencies of the low-rank structure of the sound field are explored. Based on Crow’s model [1], we use a wavepacket source to explore features of the axisymmetric mode of the radiated sound. The model considers all components of Lighthill’s stress tensor to understand the physics behind the observed trends, and this suggests a modification to Crow’s wavepacket. The model proposed reproduces qualitatively some of the different scalings observed at low and high polar angles.
\n
\n
\n
\n
A variety of actuation methods have been applied to turbulent jets with the aim of reducing far-field sound. However, a detailed understanding of the mechanisms by which actuation alters the turbulence and far-field sound is lacking. We investigate the effect of periodic acoustic forcing by performing a series of large-eddy simulations of turbulent axisymmetric subsonic and supersonic jets subjected to periodic forcing at several frequencies and amplitudes. To analyze data from the forced jets, we employ cyclostationary analysis, which is an extension of the statistically stationary framework to processes that have periodically varying statistics. Both low- St_f=0.3 and high-frequency St_f=1.5 forcing generate an energetic tonal response but have limited effect on the time-averaged mean with a forcing amplitude greater than 1% required to achieve a small change. Similar trends were seen for the turbulent kinetic energy and the energy transfer between the mean and turbulent components. By applying cyclostationary spectral proper orthogonal decomposition (CS-SPOD), we investigate how the dominant coherent structures are modified and modulated by the forcing. For St_f=0.3, a broadband increase in the energy of the dominant coherent structures was found. The low-frequency coherent structures were found to be strongly phase dependent, with substantial energy coupled to the high-velocity and high-shear regions of the mean flow. In contrast, forcing at St_f=1.5 resulted in a broadband decrease in the energy of the dominant coherent structures. No phase-dependent modulation of the low-frequency coherent structures was seen due to a large difference in the wavelength and spatial support between the coherent structures and the mean field. A reduced impact of the St_f=0.3 forcing on the supersonic jet is seen, while the St_f=1.5 forcing results in a similar impact.
\n
\n
\n
",
"doi": "10.2514/6.2023-3652",
"isbn": "978-1-62410-704-7",
"publisher": "American Institute of Aeronautics and Astronautics",
"place_of_publication": "Reston, VA",
"publication_date": "2023-06",
"pages": "2023-3652"
},
{
"id": "authors:pb1ax-1p987",
"collection": "authors",
"collection_id": "pb1ax-1p987",
"cite_using_url": "https://authors.library.caltech.edu/records/pb1ax-1p987",
"type": "conference_item",
"title": "Three-dimensional Stability and Resolvent Analysis of External Flows Over Spanwise-homogeneous Immersed Bodies",
"book_title": "AIAA AVIATION 2023 Forum",
"author": [
{
"family_name": "Hou",
"given_name": "Wei",
"clpid": "Hou-Wei"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "\n
\n
We introduce a computationally efficient method to conduct three-dimensional stability and resolvent analyses of flow around nominally two-dimensional (spanwise homogeneous) bodies of arbitrary cross-sections. For incompressible flows, our method utilizes the immersed boundary (IB) method with a fast Lattice Green's Function (FLGF) solver for the associated Poisson-like equation and includes adaptive mesh refinement (AMR). We validate our algorithm by performing stability analyses of flow past a rotating cylinder and comparing our results with ones from the literature. We also demonstrate the capability of this algorithm by conducting a 2D resolvent analysis by considering the flow past a cylinder at Re = 100. Finally, we demonstrate the capability of this method to handle a wide range of length scales by conducting stability analysis of the flow past a cylinder at Re = 63 with a small control cylinder in its wake.
\n
\n
\n
\n
We extend the One-Way Navier Stokes (OWNS) approach to support nonlinear interactions between waves of different frequencies, which will enable nonlinear analysis of instability and transition. In linear OWNS, the linearized Navier-Stokes equations are modified such that upstream propagating modes are removed, so that they can be solved efficiently in the frequency domain as a spatial initial-value (marching) problem. Linear OWNS confers numerous advantages over the parabolized stability equations (PSE) that we seek to extend to nonlinear analysis. In the proposed method, the fully nonlinear Navier-Stokes equations are marched in the downstream direction. At each step of the march, the projection operator from the linear OWNS procedure is applied to (approximately) remove modes with upstream group velocity. We validate the method by examining the nonlinear evolution of two- and three-dimensional disturbances in a low-speed Blasius boundary layer by comparing with PSE and DNS results from the literature.
\n
\n
Large-eddy simulations (LES) of a turbulent unforced jet at Re = 50,000 and M\u2c7c= 0.4, and jets forced at azimuthal wavenumbers m = 0, m = 1, m = 2 and m = 6 are performed. The objective of this study is to characterize the nonlinear interactions that are initiated by the forcing. To achieve this, we used the bispectral mode decomposition (BMD) technique, which is tailored to extract flow structures associated with triadic interactions. Azimuthal wavenumber triads are investigated using the cross-spectral variant of BMD. Axisymmetric forcing generates peaks at the forcing frequency and its harmonics in the m = 0 component only, whereas non-axisymmetric forcing generates peaks at different azimuthal wavenumbers. The latter aspect is investigated using cross-BMD. Forcing the jet at m = 1, the only odd-m forcing case considered, creates a cascade of triads that generates peaks at the forcing frequency and its odd harmonics at odd azimuthal wavenumbers and even harmonics at even azimuthal wavenumbers. Forcing the jet at m = m_f azimuthal wavenumbers produces peaks at the odd harmonics in the odd integer multiples of m_f and at even harmonic frequencies in the even integer multiples of m_f.
",
"doi": "10.2514/6.2023-3651",
"isbn": "978-1-62410-704-7",
"publisher": "American Institute of Aeronautics and Astronautics",
"place_of_publication": "Reston, VA",
"publication_date": "2023-06",
"pages": "2023-3651"
},
{
"id": "authors:hym75-7g327",
"collection": "authors",
"collection_id": "hym75-7g327",
"cite_using_url": "https://authors.library.caltech.edu/records/hym75-7g327",
"type": "conference_item",
"title": "Cavitation Inside Droplets Induced by Shocks",
"author": [
{
"family_name": "Chreim",
"given_name": "Jose Rodolfo",
"orcid": "0000-0002-2809-9116",
"clpid": "Chreim-Jose-Rodolfo"
},
{
"family_name": "Rodriguez",
"given_name": "Mauro, Jr.",
"orcid": "0000-0003-0545-0265",
"clpid": "Rodriguez-Mauro-Jr"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We simulate the interactions of a water droplet and shock wave, focusing on early stages as the internally reflected
waves decrease the droplet minimum pressure and can induce cavitation, thereby latering the breakup process.
Results show how the minimum pressure evolve and is affected by the presence of a small air cavity, significantly
decreasing the its magnitude. By the final abstract deadline, the authors expect to include simulations in which
phase-change is activated such that regions of water vapor are generated as a consequence of the minimum pressure
being below the cavitation threshold.
",
"doi": "10.7907/hym75-7g327",
"publisher": "California Institute of Technology",
"publication_date": "2023-04-04"
},
{
"id": "authors:6xmqz-jdr98",
"collection": "authors",
"collection_id": "6xmqz-jdr98",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230530-441187700.29",
"type": "article",
"title": "Conditional moment methods for polydisperse cavitating flows",
"author": [
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-Spencer-H"
},
{
"family_name": "Fox",
"given_name": "Rodney O.",
"orcid": "0000-0003-1944-1861",
"clpid": "Fox-Rodney-O"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The dynamics of cavitation bubbles are important in many flows, but their small sizes and high number densities often preclude direct numerical simulation. We present a computational model that averages their effect on the flow over larger spatiotemporal scales. The model is based on solving a generalized population balance equation (PBE) for nonlinear bubble dynamics and explicitly represents the evolving probability density of bubble radii and radial velocities. Conditional quadrature-based moment methods (QBMMs) are adapted to solve this PBE. A one-way-coupled bubble dynamics problem demonstrates the efficacy of different QBMMs for the evolving bubble statistics. Results show that enforcing hyperbolicity during moment inversion (CHyQMOM) provides comparable model-form accuracy to the traditional conditional method of moments and decreases computational costs by about ten times for a broad range of test cases. The CHyQMOM-based computational model is implemented in MFC, an open-source multi-phase and high-order-accurate flow solver. We assess the effect of the model and its parameters on a two-way coupled bubble screen flow problem.",
"doi": "10.1016/j.jcp.2023.111917",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2023-03-15",
"volume": "477",
"pages": "111917"
},
{
"id": "authors:mx52g-98593",
"collection": "authors",
"collection_id": "mx52g-98593",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230227-87934600.8",
"type": "article",
"title": "Global receptivity analysis: physically realizable input-output analysis",
"author": [
{
"family_name": "Kamal",
"given_name": "Omar",
"orcid": "0000-0002-3431-2964",
"clpid": "Kamal-Omar"
},
{
"family_name": "Lakebrink",
"given_name": "Matthew T.",
"clpid": "Lakebrink-Matthew-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "In the context of transition analysis, linear input\u2013output analysis determines the worst-case disturbances to a laminar base flow based on a generic right-hand-side volumetric/boundary forcing term. The worst-case forcing is not physically realizable, and, to our knowledge, a generic framework for posing physically realizable worst-case disturbance problems is lacking. In natural receptivity analysis, disturbances are forced by matching (typically local) solutions within the boundary layer to outer solutions consisting of free-stream vortical, entropic and acoustic disturbances. We pose a scattering formalism to restrict the input forcing to a set of realizable disturbances associated with plane-wave solutions of the outer problem. The formulation is validated by comparing with direct numerical simulations of a Mach 4.5 flat-plate boundary layer. We show that the method provides insight into transition mechanisms by identifying those linear combinations of plane-wave disturbances that maximize energy amplification over a range of frequencies. We also discuss how the framework can be extended to accommodate scattering from shocks and in shock layers for supersonic flow.",
"doi": "10.1017/jfm.2023.48",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2023-02-10",
"volume": "956",
"pages": "Art. No. R5"
},
{
"id": "authors:mr3c8-7n898",
"collection": "authors",
"collection_id": "mr3c8-7n898",
"cite_using_url": "https://authors.library.caltech.edu/records/mr3c8-7n898",
"type": "book_section",
"title": "Boundary conditions for turbulence simulation",
"book_title": "Numerical Methods in Turbulence Simulation",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"editor": [
{
"family_name": "Moser",
"given_name": "Robert D.",
"orcid": "0000-0001-7735-1253",
"clpid": "Moser-Robert-D"
}
],
"abstract": "\n
\n
\n
\n
Physically realistic, mathematically well-posed boundary conditions (BC) are needed to close the system of partial differential equations representing a turbulent flow. BCs play a key role in establishing physically meaningful simulations. There is an interplay between the choice and implementation of BCs and the underlying discretization method. It is important to ensure that any artifacts of discretization or numerical parameters have controllable impacts on the turbulence. The aims of this chapter are review strategies for posing BCs for the incompressible and compressible Navier–Stokes equations, and to arm the student with “good” boundary conditions, understand what the existing techniques can and cannot do, and to provide some tools for assessing their impact on the quality of the turbulence simulation.
\n
\n
\n
\n
Energy harvesters are candidates for achieving the self-powering of flow sensing systems. We present an analysis of the energy transfer mechanisms occurring in internal flow electromagnetic devices. The focus is on derivating the expressions that describe the coupling between the electromagnetic, flow and structural systems. We analyze the physics of the mechanisms that dominate the conversion of flow kinetic energy into electricity and propose a metric for the harvester's efficiency.
",
"issn": "2591-3522",
"publisher": "Asociaci\u00f3n Argentina de Mec\u00e1nica Computacional",
"publication": "Mec\u00e1nica Computacional",
"publication_date": "2022-11",
"series_number": "27",
"volume": "XXXIX",
"issue": "27",
"pages": "967"
},
{
"id": "authors:s9t60-zgj64",
"collection": "authors",
"collection_id": "s9t60-zgj64",
"cite_using_url": "https://authors.library.caltech.edu/records/s9t60-zgj64",
"type": "article",
"title": "An Adaptive, Scalable, and Robust Approach for Computing External Flows via the Immersed Boundary Method",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The immersed boundary (IB) method enables computation of flows in a wide array of complex geometries with far easier meshing compared to traditional body-fitted discretization, particularly for moving/deforming bodies. Retaining an underlying Cartesian mesh is likewise very favorable for developing robust (conservative, stable), efficient, and scalable algorithms that can preserve many of the important symmetries and invariants of the continuous equations of motion. On the other hand, a grid with fixed resolution is inefficient for resolving multi scale features such as thin boundary layers. We describe recent efforts to equip an IB method with two features that alleviate these constraints while maintaining the benefits of the Cartesian mesh. These are the use of a lattice Green’s function solver (implemented with a scalable, linear-complexity fast multipole method) and block-wise adaptive mesh refinement. We highlight the capabilities of the solver by computing flows over bluff and streamlined bodies at high Reynolds number.
",
"issn": "2591-3522",
"publisher": "Asociaci\u00f3n Argentina de Mec\u00e1nica Computacional",
"publication": "Mec\u00e1nica Computacional",
"publication_date": "2022-11",
"series_number": "1",
"volume": "XXXIX",
"issue": "1",
"pages": "3"
},
{
"id": "authors:n1agd-f0d55",
"collection": "authors",
"collection_id": "n1agd-f0d55",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20230502-987371300.5",
"type": "article",
"title": "Efficient global resolvent analysis via the one-way Navier-Stokes equations",
"author": [
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-Aaron"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-Georgios"
},
{
"family_name": "Kamal",
"given_name": "Omar",
"orcid": "0000-0002-3431-2964",
"clpid": "Kamal-Omar"
},
{
"family_name": "Pickering",
"given_name": "Ethan",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-Ethan-M"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Resolvent analysis is a powerful tool for modelling and analysing transitional and turbulent flows and, in particular, for approximating coherent flow structures. Despite recent algorithmic advances, computing resolvent modes for flows with more than one inhomogeneous spatial coordinate remains computationally expensive. In this paper we show how efficient and accurate approximations of resolvent modes can be obtained using a well-posed spatial marching method for flows that contain a slowly varying direction, i.e. one in which the mean flow changes gradually. First, we derive a well-posed and convergent one-way equation describing the downstream-travelling waves supported by the linearized Navier\u2013Stokes equations. The method is based on a projection operator that isolates downstream-travelling waves. Integrating these one-way Navier\u2013Stokes (OWNS) equations in the slowly varying direction, which requires significantly less CPU and memory resources than a direct solution of the linearized Navier\u2013Stokes equations, approximates the action of the resolvent operator on a forcing vector. Second, this capability is leveraged to compute approximate resolvent modes using an adjoint-based optimization framework in which the forward and adjoint OWNS equations are marched in the downstream and upstream directions, respectively. This avoids the need to solve direct and adjoint globally discretized equations, therefore bypassing the main computational bottleneck of a typical global resolvent calculation. The method is demonstrated using the examples of a simple acoustics problem, a Mach 1.5 turbulent jet and a Mach 4.5 transitional zero-pressure-gradient flat-plate boundary layer. The optimal OWNS results are validated against corresponding global calculations, and the close agreement demonstrates the near-parabolic nature of these flows.",
"doi": "10.1017/jfm.2022.647",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2022-10-10",
"volume": "948",
"pages": "A9"
},
{
"id": "authors:tc6t9-4wd36",
"collection": "authors",
"collection_id": "tc6t9-4wd36",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220725-156674000",
"type": "article",
"title": "Hybrid quadrature moment method for accurate and stable representation of non-Gaussian processes applied to bubble dynamics",
"author": [
{
"family_name": "Charalampopoulos",
"given_name": "A.",
"orcid": "0000-0003-4136-0363",
"clpid": "Charalampopoulos-Alexis-Tzianni"
},
{
"family_name": "Bryngelson",
"given_name": "S. H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-Spencer-H"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Sapsis",
"given_name": "T. P.",
"orcid": "0000-0003-0302-0691",
"clpid": "Sapsis-Themistoklis"
}
],
"abstract": "Solving the population balance equation (PBE) for the dynamics of a dispersed phase coupled to a continuous fluid is expensive. Still, one can reduce the cost by representing the evolving particle density function in terms of its moments. In particular, quadrature-based moment methods (QBMMs) invert these moments with a quadrature rule, approximating the required statistics. QBMMs have been shown to accurately model sprays and soot with a relatively compact set of moments. However, significantly non-Gaussian processes such as bubble dynamics lead to numerical instabilities when extending their moment sets accordingly. We solve this problem by training a recurrent neural network (RNN) that adjusts the QBMM quadrature to evaluate unclosed moments with higher accuracy. The proposed method is tested on a simple model of bubbles oscillating in response to a temporally fluctuating pressure field. The approach decreases model-form error by a factor of 10 when compared with traditional QBMMs. It is both numerically stable and computationally efficient since it does not expand the baseline moment set. Additional quadrature points are also assessed, optimally placed and weighted according to an additional RNN. These points further decrease the error at low cost since the moment set is again unchanged.",
"doi": "10.1098/rsta.2021.0209",
"issn": "1364-503X",
"publisher": "Royal Society of London",
"publication": "Philosophical Transactions A: Mathematical, Physical and Engineering Sciences",
"publication_date": "2022-08-08",
"series_number": "2229",
"volume": "380",
"issue": "2229",
"pages": "Art. No. 20210209"
},
{
"id": "authors:sf8ht-70h78",
"collection": "authors",
"collection_id": "sf8ht-70h78",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220714-848665700",
"type": "article",
"title": "Particle-Assisted Laser-Induced Inertial Cavitation for High Strain-Rate Soft Material Characterization",
"author": [
{
"family_name": "Buyukozturk",
"given_name": "S.",
"clpid": "Buyukozturk-S"
},
{
"family_name": "Spratt",
"given_name": "J.-S.",
"clpid": "Spratt-Jean-Sebastien"
},
{
"family_name": "Henann",
"given_name": "D. L.",
"orcid": "0000-0002-1497-4143",
"clpid": "Henann-David-L"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Franck",
"given_name": "C.",
"orcid": "0000-0002-2347-620X",
"clpid": "Franck-Christian"
}
],
"abstract": "Background
\nWhile there are few reliable techniques for characterizing highly compliant and viscoelastic materials under large deformations, laser-induced Inertial Microcavitaton Rheometry (IMR) was recently developed to fill this void and to characterize soft materials at high to ultra-high strain rates (O(10³)∼O(10\u2078) s\u207b¹). Yet, one of the current limitations in IMR has been the dependence of the cavitation nucleation physics on the intrinsic material properties often generating extreme deformation levels and thus complicating material characterization procedures.
\nObjective
\nThe objective of this study was to develop an experimental approach for modulating laser-induced cavitation (LIC) bubble amplitudes and their resulting maximum material deformations. Lowering the material stretch ratios during inertial cavitation will provide an experimental platform of broad applicability to a large class of polymeric materials and environmental conditions.
\nMethods
\nExperimental methods include using three types of micron-sized nucleation seed particles and varying laser energies in polyacrylamide hydrogels of known concentration. Using a Quadratic law Kelvin-Voigt material model, we implemented ensemble-based data assimilation (DA) techniques to robustly quantify the nonlinear constitutive material parameters, up through the first, second, and third bubble collapse cycles. Fitted values were then used to simulate bubble dynamics to compute critical bubble collapse Mach numbers, and to assess time-varying uncertainties of the full cavitation dynamics with respect to the current state-of-the art theoretical model featured in the IMR model.
\nResults
\nWhile varying laser energy modulated bubble amplitude, seed particles successfully expanded (more than doubled) the finite deformation regime (i.e., maximum material stretch, λ\u2098\u2090\u2093 ≈ 4 - 9). Comparing experimental data to IMR simulations, we found that fitting beyond the first bubble collapse, as well as increasing laser energy, increased the bubble radius fit error, and larger λ\u2098\u2090\u2093 values exhibited increasingly violent bubble behavior (marked by increasing collapse Mach numbers greater than 0.08). Additionally, time-varying analysis showed the greatest model uncertainty during initial bubble collapse, where bubbles nucleated at lower laser energies and resulting λ\u2098\u2090\u2093 had less uncertainty at collapse compared to higher laser energy and λ\u2098\u2090\u2093 cases.
\nConclusions
\nThis study indicates IMR’s current theoretical framework might be lacking important additional cavitation and/or material physics. However, expanding the finite deformation regime of soft materials to attain lower stretch regimes enables broader applicability to a larger class of soft polymeric materials and will enable future, systematic development and incorporation of more complex physics and constitutive models including damage and failure mechanisms into the theoretical framework of IMR.
",
"doi": "10.1007/s11340-022-00861-7",
"issn": "0014-4851",
"publisher": "Springer",
"publication": "Experimental Mechanics",
"publication_date": "2022-07",
"series_number": "6",
"volume": "62",
"issue": "6",
"pages": "1037-1050"
},
{
"id": "authors:32wtz-93209",
"collection": "authors",
"collection_id": "32wtz-93209",
"cite_using_url": "https://authors.library.caltech.edu/records/32wtz-93209",
"type": "conference_item",
"title": "Triadic nonlinear interactions and acounstics of forced versus unforced turbulent jets",
"book_title": "Proceedings of TSFP-12 (2022) Osaka",
"author": [
{
"family_name": "Nekkanti",
"given_name": "Akhil",
"orcid": "0000-0002-2173-8704",
"clpid": "Nekkanti-Akhil"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-Oliver-T"
},
{
"family_name": "Maia",
"given_name": "Igor"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-Peter"
},
{
"family_name": "Heidt",
"given_name": "Liam",
"clpid": "Heidt-Liam"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We explore the potential of bispectral mode decomposition (BMD) for physical discovery in jet flows. BMD is a modal decomposition that is tailored to the extraction of flow structures involved in triadic interactions. Large-eddy simulations (LES) of turbulent forced and unforced round jets at Re = 50,000 and Mj = 0.4 are conducted and validated with the companion experiment at the Institut Pprime. The comparative BMD analysis reveals that triadic interactions in both forced and unforced jets are most prevalent in a welldefined region near and downstream of the closure of the potential core. A BMD analysis of far-field pressure sheds light on the previously reported observation that differenceinteractions are more efficient radiators of jet noise than the sum-interactions.
",
"publisher": "Darmstadt University of Technology",
"publication_date": "2022-07",
"pages": "149"
},
{
"id": "authors:a80y9-vv085",
"collection": "authors",
"collection_id": "a80y9-vv085",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220412-864423600",
"type": "article",
"title": "Improving burst wave lithotripsy effectiveness for small stones and fragments by increasing frequency: theoretical modeling and ex vivo study",
"author": [
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-Michael-R"
},
{
"family_name": "Maxwell",
"given_name": "Adam D.",
"clpid": "Maxwell-Adam-D"
},
{
"family_name": "Cao",
"given_name": "Shunxiang",
"clpid": "Cao-Shunxiang"
},
{
"family_name": "Ramesh",
"given_name": "Shivani",
"clpid": "Ramesh-Shivani"
},
{
"family_name": "Liu",
"given_name": "Ziyue",
"clpid": "Liu-Ziyue"
},
{
"family_name": "Williams",
"given_name": "James Caldwell, Jr.",
"clpid": "Williams-James-Caldwell-Jr"
},
{
"family_name": "Thiel",
"given_name": "Jeff",
"clpid": "Thiel-Jeff"
},
{
"family_name": "Dunmire",
"given_name": "Barbrina",
"clpid": "Dunmire-Barbrina"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Kuznetsova",
"given_name": "Ekaterina",
"clpid": "Kuznetsova-Ekaterina"
},
{
"family_name": "Kreider",
"given_name": "Wayne",
"clpid": "Kreider-Wayne"
},
{
"family_name": "Sorensen",
"given_name": "Mathew D.",
"clpid": "Sorensen-Mathew-D"
},
{
"family_name": "Lingeman",
"given_name": "James E.",
"clpid": "Lingeman-James-E"
},
{
"family_name": "Sapozhnikov",
"given_name": "Oleg A.",
"clpid": "Sapozhnikov-Oleg-A"
}
],
"abstract": "\n
Introduction and Objective:
\n
In clinical trial NCT03873259, a 2.6-mm lower pole stone was treated transcutaneously and ex vivo with 390-kHz burst wave lithotripsy (BWL) for 40 minutes and failed to break. The stone was subsequently fragmented with 650-kHz BWL after a 4-minute exposure. This study investigated how to fragment small stones and why varying the BWL frequency may more effectively fragment stones to dust.
\n
\n
Methods:
\n
A linear elastic theoretical model was used to calculate the stress created inside stones from shock wave lithotripsy (SWL) and different BWL frequencies mimicking the stone's size, shape, lamellar structure, and composition. To test model predictions about the impact of BWL frequency, matched pairs of stones (1–5 mm) were treated at (1) 390 kHz, (2) 830 kHz, and (3) 390 kHz followed by 830 kHz. The mass of fragments >1 and 2 mm was measured over 10 minutes of exposure.
\n
\n
Results:
\n
The linear elastic model predicts that the maximum principal stress inside a stone increases to more than 5.5 times the pressure applied by the ultrasound wave as frequency is increased, regardless of the composition tested. The threshold frequency for stress amplification is proportionate to the wave speed divided by the stone diameter. Thus, smaller stones may be likely to fragment at a higher frequency, but not at a lower frequency below a limit. Unlike with SWL, this amplification in BWL occurs consistently with spherical and irregularly shaped stones. In water tank experiments, stones smaller than the threshold size broke fastest at high frequency (p = 0.0003), whereas larger stones broke equally well to submillimeter dust at high, low, or mixed frequencies.
\n
\n
Conclusions:
\n
For small stones and fragments, increasing frequency of BWL may produce amplified stress in the stone causing the stone to break. Using the strategies outlined here, stones of all sizes may be turned to dust efficiently with BWL.
\n
The present study proposes a framework of the superresolution measurement based on the dynamic mode decomposition (DMD) with the Kalman filter and Rauch–Tung–Striebel smoother. The dual-planar particle image velocimetry (PIV) systems were constructed to acquire the paired velocity fields of a Mach 1.1 supersonic jet. The acoustic measurement was simultaneously performed, and the velocity and acoustic data are used for the superresolution. Although the dual PIV system measures the basic characteristics of the velocity fields, all the DMD modes calculated by the exact DMD are decay modes due to the measurement noise. The superresolved velocity field shows smooth convection of the large-scale structures at the downstream side. Therefore, the proposed method is effective to reconstruct the entire flow fluctuation because the DMD modes express the linear dynamical system of the velocity fields.
",
"doi": "10.2514/6.2022-3065",
"isbn": "978-1-62410-664-4",
"publisher": "American Institute of Aeronautics and Astronautics",
"place_of_publication": "Reston, VA",
"publication_date": "2022-06-14",
"pages": "2022-3065"
},
{
"id": "authors:e8rn0-34s44",
"collection": "authors",
"collection_id": "e8rn0-34s44",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220708-930729800",
"type": "conference_item",
"title": "Assessment of Linear Methods for Analysis of Boundary Layer Instabilities on a Finned Cone at Mach 6",
"book_title": "AIAA AVIATION 2022 Forum",
"author": [
{
"family_name": "Araya",
"given_name": "Daniel",
"clpid": "Araya-Daniel-B"
},
{
"family_name": "Bitter",
"given_name": "Neal",
"clpid": "Araya-Neal"
},
{
"family_name": "Wheaton",
"given_name": "Bradley M.",
"orcid": "0009-0005-5765-0316",
"clpid": "Wheaton-Bradley-M"
},
{
"family_name": "Kamal",
"given_name": "Omar",
"orcid": "0000-0002-3431-2964",
"clpid": "Kamal-Omar"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Knutson",
"given_name": "Anthony",
"clpid": "Knutson-Anthony"
},
{
"family_name": "Johnson",
"given_name": "Heath",
"clpid": "Johnson-Heath"
},
{
"family_name": "Nichols",
"given_name": "Joseph",
"clpid": "Nichols-Joseph"
},
{
"family_name": "Candler",
"given_name": "Graham V.",
"clpid": "Candler-Graham-V"
},
{
"family_name": "Russo",
"given_name": "Vincenzo",
"clpid": "Russo-Vincenzo"
},
{
"family_name": "Brehm",
"given_name": "Christoph",
"orcid": "0000-0002-9006-3587",
"clpid": "Brehm-Christoph"
}
],
"abstract": "Boundary-layer instabilities of a finned cone at Mach = 6, Re = 8.4 x 10\u2076 /m, and zero incidence angle are examined using linear stability methods of varying fidelity and maturity. The geometry and laminar flow conditions correspond to experiments conducted at the Boeing Air Force Mach 6 Quiet Tunnel (BAM6QT) at Purdue University. Where possible, a common mean flow is utilized among the stability computations, and comparisons are made along the acreage of the cone where transition is first observed in the experiment. Stability results utilizing Linear Stability Theory (LST), planar Parabolized Stability Equations (planar-PSE), One-Way Navier Stokes (OWNS), forced direct numerical simulation (DNS), and Adaptive Mesh Refinement Wavepacket Tracking (AMR-WPT) are presented. One of the major findings of the work includes identification of a dominant three-dimensional vortex instability occurring at approximately 250 kHz that correlates well with experimental measurements of transition onset. With the exception of LST, all of the higher-fidelity linear methods considered in this work were consistent in predicting the initial growth and general structure of the vortex instability as it evolved downstream. OWNS analysis utilizing randomized wavenumber forcing identified possible nonmodal interactions contributing to the development of this vortex instability. Both forced DNS and AMR-WPT analysis demonstrated the utility of these methods in tracking either linear or nonlinear growth of disturbances. Finally, a new implementation of Input/Output (I/O) analysis is discussed and some of the challenges, opportunities, and development needs for all of the stability methods are presented.
",
"doi": "10.2514/6.2022-3247",
"isbn": "978-1-62410-635-4",
"publisher": "American Institute of Aeronautics and Astronautics",
"place_of_publication": "Reston, VA",
"publication_date": "2022-06",
"pages": "2022-3247"
},
{
"id": "authors:73t32-zaw93",
"collection": "authors",
"collection_id": "73t32-zaw93",
"cite_using_url": "https://authors.library.caltech.edu/records/73t32-zaw93",
"type": "conference_item",
"title": "Estimation of Time-Resolved Three-Dimensional Velocity Fields of Underexpanded Jets in Flapping Screech Mode",
"book_title": "28th AIAA/CEAS Aeroacoustics 2022 Conference",
"author": [
{
"family_name": "Lee",
"given_name": "Chungil",
"orcid": "0000-0002-3629-427X",
"clpid": "Lee-Chungil"
},
{
"family_name": "Nishikori",
"given_name": "Hiroki",
"clpid": "Nishikori-Hiroki"
},
{
"family_name": "Nagata",
"given_name": "Takayuki",
"orcid": "0000-0003-3644-4888",
"clpid": "Nagata-Takayuki"
},
{
"family_name": "Ozawa",
"given_name": "Yuta",
"orcid": "0000-0002-5895-0506",
"clpid": "Ozawa-Yuta"
},
{
"family_name": "Nonomura",
"given_name": "Taku",
"orcid": "0000-0001-7739-7104",
"clpid": "Nonomura-Taku"
},
{
"family_name": "Asai",
"given_name": "Keisuke",
"orcid": "0000-0002-9330-4972",
"clpid": "Asai-Keisuke"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "\n
\n
A method for estimating time-resolved three-dimensional velocity fields from non-time-resolved particle image velocimetry (PIV) and time-resolved near-field acoustic data is proposed and evaluated on a screeching, underexpanded jet. Multi-time-delay modified linear stochastic estimation (MTD-mLSE) is applied to the reduced-order PIV data and the Fourier coefficients of the azimuthal modes of sound pressure data of eight microphones arranged in a ring. The dominant screech tone at a nozzle pressure ratio of 2.97 corresponds to the first asymmetric mode. Time-resolved three-dimensional velocity fields corresponding to this mode are estimated, and flow structures associated with the flapping oscillation are observed. The obtained result shows that the velocity fluctuations are large near the screech source location of the B (flapping) screech mode.
\n
\n
A flow energy harvesting system including a nozzle-diffuser defining a spline-shaped flow channel and a flow energy harvesting device in the spline-shaped flow channel of the nozzle-diffuser. The spline-shaped flow channel includes a converging portion, a diverging portion, and a constriction section between the converging and diverging portions. The flow energy harvesting device includes a flextensional member having a frame and a cantilever extending outward from the frame, and a stack of piezoelectric elements housed in an interior cavity defined in the frame. The cantilever is a non-piezoelectric material. The frame of the flextensional member is in the converging portion and the cantilever is in the constriction section of the spline-shaped flow channel. The frame is configured to deform and elongate the piezoelectric elements to generate a current based on the piezoelectric effect when a fluid flows through the spline-shaped flow channel and generates unbalanced forces on the cantilever due.
",
"publisher": "U.S. Patent Office",
"publication_date": "2022-04-26"
},
{
"id": "authors:hhvz7-7kw87",
"collection": "authors",
"collection_id": "hhvz7-7kw87",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20231006-181214305",
"type": "article",
"title": "Introduction to the special issue on supersonic jet noise",
"author": [
{
"family_name": "Wall",
"given_name": "Alan T.",
"clpid": "Wall-Alan-T"
},
{
"family_name": "Gee",
"given_name": "Kent L.",
"orcid": "0000-0002-5768-6483",
"clpid": "Gee-Kent-L"
},
{
"family_name": "Morrison",
"given_name": "Philip J.",
"clpid": "Morrison-Philip-J"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lowe",
"given_name": "K. Todd",
"clpid": "Lowe-K-Todd"
}
],
"abstract": "This editorial's goals are (1) to highlight a few key developments in supersonic jet and launch vehicle noise research over the past several decades while describing some of the critical modern requirements facing government and industry organizations and (2) to summarize the contributions of the articles in this Supersonic Jet Noise special issue in the context of these developments and requirements.",
"doi": "10.1121/10.0009321",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2022-02",
"series_number": "2",
"volume": "151",
"issue": "2",
"pages": "806-816"
},
{
"id": "authors:0hhbz-ew663",
"collection": "authors",
"collection_id": "0hhbz-ew663",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211213-518510000",
"type": "article",
"title": "Real-time supersonic jet noise predictions from near-field sensors with a wavepacket model",
"author": [
{
"family_name": "Kleine",
"given_name": "Vitor G.",
"clpid": "Kleine-Vitor-G"
},
{
"family_name": "Sasaki",
"given_name": "Kenzo",
"orcid": "0000-0002-3347-4996",
"clpid": "Sasaki-Kenzo"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-Andr\u00e9-V-G"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-Guillaume-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Parabolized stability equations (PSE) have been shown to model wavepackets and, consequently, the near-field of turbulent jets with reasonable accuracy. In this work, PSE were employed to obtain a reduced-order model that could estimate both the fluid-dynamic and the acoustic fields of a supersonic jet in a computationally efficient approximation for resolvent-based estimation based on a single input. From the unsteady pressure data at an input position, the time-domain pressure field was estimated using transfer functions obtained using PSE and a data-driven method based on a well-validated large-eddy simulation (LES). The prediction scheme employed is a single-input single-output, linear model. The unsteady pressure predicted by the PSE showed good agreement with the LES results, especially if the input position is outside the mixing layer, where the prediction capabilities of the PSE are comparable to those of the data-driven transfer functions. The good agreement indicates that PSE could not only be used to predict the sound generation but also to open up different potentialities to attenuate the noise by flow control. The exploration of the regions where the method displayed good agreement, which are presented in this work, can guide the positioning of the sensors for experimental implementation of closed-loop control in a jet.",
"doi": "10.1121/10.0008973",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2021-12",
"series_number": "6",
"volume": "150",
"issue": "6",
"pages": "4297-4307"
},
{
"id": "authors:wqjqn-cyt06",
"collection": "authors",
"collection_id": "wqjqn-cyt06",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210323-142327998",
"type": "article",
"title": "Resolvent-based modeling of turbulent jet noise",
"author": [
{
"family_name": "Pickering",
"given_name": "Ethan",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-Ethan-M"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-Aaron"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-Peter"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Resolvent analysis has demonstrated encouraging results for modeling coherent structures in jets when compared against their data-educed counterparts from high-fidelity large-eddy simulations (LES). We formulate resolvent analysis as an acoustic analogy that relates the near-field resolvent forcing to the near- and far-field pressure. We use an LES database of round, isothermal, Mach 0.9 and 1.5 jets to produce an ensemble of realizations for the acoustic field that we project onto a limited set of resolvent modes. In the near-field, we perform projections on a restricted acoustic output domain, r/D = [5,6], while the far-field projections are performed on a Kirchhoff surface comprising a 100-diameter arc centered at the nozzle. This allows the LES realizations to be expressed in the resolvent basis via a data-deduced, low-rank, cross-spectral density matrix. We find that a single resolvent mode reconstructs the most energetic regions of the acoustic field across Strouhal numbers, St = [0\u22121], and azimuthal wavenumbers, m = [0,2]. Finally, we present a simple function that results in a rank-1 resolvent model agreeing within 2\u2009dB of the peak noise for both jets.",
"doi": "10.1121/10.0006453",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2021-10",
"series_number": "4",
"volume": "150",
"issue": "4",
"pages": "2421-2433"
},
{
"id": "authors:t7yrg-2x483",
"collection": "authors",
"collection_id": "t7yrg-2x483",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200526-130056704",
"type": "article",
"title": "MFC: An open-source high-order multi-component, multi-phase, and multi-scale compressible flow solver",
"author": [
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-Spencer-H"
},
{
"family_name": "Schmidmayer",
"given_name": "Kevin",
"orcid": "0000-0003-0444-3098",
"clpid": "Schmidmayer-Kevin"
},
{
"family_name": "Coralic",
"given_name": "Vedran",
"clpid": "Coralic-Vedran"
},
{
"family_name": "Meng",
"given_name": "Jomela C.",
"orcid": "0000-0002-8966-2291",
"clpid": "Meng-Jomela-Chen-Chen"
},
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "MFC is an open-source tool for solving multi-component, multi-phase, and bubbly compressible flows. It is capable of efficiently solving a wide range of flows, including droplet atomization, shock\u2013bubble interaction, and bubble dynamics. We present the 5- and 6-equation thermodynamically-consistent diffuse-interface models we use to handle such flows, which are coupled to high-order interface-capturing methods, HLL-type Riemann solvers, and TVD time-integration schemes that are capable of simulating unsteady flows with strong shocks. The numerical methods are implemented in a flexible, modular framework that is amenable to future development. The methods we employ are validated via comparisons to experimental results for shock\u2013bubble, shock\u2013droplet, and shock\u2013water\u2013cylinder interaction problems and verified to be free of spurious oscillations for material-interface advection and gas\u2013liquid Riemann problems. For smooth solutions, such as the advection of an isentropic vortex, the methods are verified to be high-order accurate. Illustrative examples involving shock\u2013bubble\u2013vessel-wall and acoustic\u2013bubble\u2013net interactions are used to demonstrate the full capabilities of MFC.",
"doi": "10.1016/j.cpc.2020.107396",
"pmcid": "PMC8218895",
"issn": "0010-4655",
"publisher": "Elsevier",
"publication": "Computer Physics Communications",
"publication_date": "2021-09",
"volume": "266",
"pages": "Art. No. 107396"
},
{
"id": "authors:c7gv7-fst22",
"collection": "authors",
"collection_id": "c7gv7-fst22",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211008-183534650",
"type": "book_section",
"title": "Analysis of forced subsonic jets using spectral proper orthogonal decomposition and resolvent analysis",
"book_title": "AIAA AVIATION 2021 Forum",
"author": [
{
"family_name": "Heidt",
"given_name": "Liam",
"clpid": "Heidt-Liam"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Nekkanti",
"given_name": "Akhil",
"orcid": "0000-0002-2173-8704",
"clpid": "Nekkanti-Akhil"
},
{
"family_name": "Schmdit",
"given_name": "Oliver",
"clpid": "Schmdit-Oliver"
},
{
"family_name": "Maia",
"given_name": "Igor",
"clpid": "Maia-Igor"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-Peter"
}
],
"abstract": "Various passive and active control strategies have been applied to turbulent jets and have achieved up to about a 5dB reduction in overall sound pressure level. However, the mechanisms by which forcing alters the turbulence and far-field sound are poorly understood. We investigate the effect of forcing by performing large-eddy simulations of turbulent axisymmetric jets subjected to periodic forcing at multiple frequencies and amplitudes. Spectral proper orthogonal decomposition is used to study the effect of the forcing on the linear spectrum. Low-frequency periodic forcing, with St_f = 0.3, while producing highly energetic tonal structures and noise, has a limited effect upon the underlying turbulent spectrum of the jet and the most energetic modes. High levels of forcing, 1% of the jet velocity, are required to achieve a small change to the turbulent mean flow and a minor shift in the turbulent spectrum. The changes in the overall spectrum and the shift in the modes are predicted well via the resolvent analysis performed on the new turbulent mean flow. This shows that the turbulent spectrum stems from the turbulent mean flow and not via interactions between phase-locked structures and the natural turbulence. High-frequency periodic forcing, with St_f = 1.5, is less effective at altering the mean flow field compared to the low-frequency forcing at the same amplitude, but results in a nonlinear interaction, potentially associated with vortex pairing, amplifying the turbulence spectrum at St ~ 0.75.",
"doi": "10.2514/6.2021-2108",
"isbn": "978-1-62410-610-1",
"publisher": "American Institute of Aeronautics and Astronautics",
"place_of_publication": "Reston, VA",
"publication_date": "2021-08-02",
"pages": "Art. No. 2021-2108"
},
{
"id": "authors:2bcxf-5w302",
"collection": "authors",
"collection_id": "2bcxf-5w302",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210811-192602670",
"type": "conference_item",
"title": "Towards large-eddy simulations of supersonic jets from twin rectangular nozzle with plasma actuation",
"book_title": "AIAA Aviation 2021 Forum",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-Guillaume-A"
},
{
"family_name": "Yeung",
"given_name": "Brandon",
"clpid": "Yeung-Brandon"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-Oliver-T"
},
{
"family_name": "Ghassemi Isfahani",
"given_name": "Ata",
"clpid": "Ghassemi-Isfahani-Ata"
},
{
"family_name": "Webb",
"given_name": "Nathan J.",
"orcid": "0000-0003-3900-1134",
"clpid": "Webb-Nathan-J"
},
{
"family_name": "Samimy",
"given_name": "Mo",
"orcid": "0000-0003-0234-9655",
"clpid": "Samimy-Mo"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Large-eddy simulation of a jet issuing from rectangular nozzles of aspect ratio 2 is performed. The nozzles are operating at their nominal design Mach number of 1.5. This operating condition and the geometry match those of the companion experiment conducted at Ohio State University. The preliminary results show good agreement with near-field and far-field noise measurements in terms of broadband levels and predictions of screech tone frequencies and amplitudes. In particular, the main noise radiation towards the aft angles and the overall sound pressure level directivity are within 1dB for most relevant frequencies and angles. For future simulations of active control, a numerical model of a localized arc filament plasma actuator is implemented and tested in a small test domain inside one of the nozzles. A grid resolution study is conducted to investigate the minimum grid resolution required for correct energy transport within the boundary layer.",
"doi": "10.2514/6.2021-2154",
"isbn": "978-1-62410-610-1",
"publisher": "American Institute of Aeronautics and Astronautics",
"place_of_publication": "Reston, VA",
"publication_date": "2021-08-02",
"pages": "Art. No. 2021-2154"
},
{
"id": "authors:htf3g-dcx05",
"collection": "authors",
"collection_id": "htf3g-dcx05",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210603-160013203",
"type": "article",
"title": "An empirical correlation between lift and the properties of leading-edge vortices",
"author": [
{
"family_name": "Jardin",
"given_name": "T.",
"orcid": "0000-0001-9704-2984",
"clpid": "Jardin-Thierry"
},
{
"family_name": "Choi",
"given_name": "J.",
"clpid": "Choi-Jeesoon"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Using data from numerical simulations, we show that the lift experienced by both impulsively started and surging airfoils correlates well with the sum of the circulation of the leading-edge vortices truncated at the trailing edge. Therefore, we suggest that reasonable estimates of the lift can be obtained using only two vortex parameters, i.e., its circulation and its position. In addition to being convenient for non-intrusive estimation of forces from PIV measurements, we show that this approach can be used to derive low-order models for the analysis of vortex-lift configurations. In particular, we apply this correlation to model high-amplitude surging, which allows us to quantify the effect of wake-capture mechanisms and to determine the flow parameters that drive optimal lift.",
"doi": "10.1007/s00162-021-00567-x",
"issn": "0935-4964",
"publisher": "Springer",
"publication": "Theoretical and Computational Fluid Dynamics",
"publication_date": "2021-08",
"series_number": "4",
"volume": "35",
"issue": "4",
"pages": "437-448"
},
{
"id": "authors:mfnan-yt466",
"collection": "authors",
"collection_id": "mfnan-yt466",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211008-210434815",
"type": "book_section",
"title": "Input/Output Analysis of Hypersonic Boundary Layers using the One-Way Navier-Stokes (OWNS) Equations",
"book_title": "AIAA Aviation 2021 Forum",
"author": [
{
"family_name": "Kamal",
"given_name": "Omar",
"clpid": "Kamal-Omar"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-Georgios"
},
{
"family_name": "Lakebrink",
"given_name": "Matthew",
"clpid": "Lakebrink-Matthew"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Accurate prediction of linear amplification of disturbances in hypersonic boundary layers is computationally challenging. While direct numerical simulations and global analysis can be used to compute optimal (worst-case) forced responses, their large computational expense render these tools less practical for large design parameter spaces. At the same time, parabolized stability equations can be unreliable for problems involving multi-modal and non-modal interactions. To bridge this gap, we apply an approximate fast marching technique, the One-Way Navier-Stokes (OWNS) Equations, in iterative fashion to solve for optimal disturbances. OWNS approximates a rigorous parabolization of the equations of motion by removing disturbances with upstream group velocity using a higher-order recursive filter. Using OWNS, we aim to characterize disturbances of flat-plate and complex-geometry hypersonic boundary layers over a range of Mach numbers, and find optimal disturbances under different cost functions that define corresponding receptivity problems. The calculation of optimal disturbances reveals multi-modal transition scenarios depending on the spatial support, frequency, and physical nature of the external disturbances.",
"doi": "10.2514/6.2021-2827",
"isbn": "978-1-62410-610-1",
"publisher": "American Institute of Aeronautics and Astronautics",
"place_of_publication": "Reston, VA",
"publication_date": "2021-08",
"pages": "Art. No. 2021-2827"
},
{
"id": "authors:df34c-fxa18",
"collection": "authors",
"collection_id": "df34c-fxa18",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200908-152555309",
"type": "article",
"title": "Characterizing viscoelastic materials via ensemble-based data assimilation of bubble collapse observations",
"author": [
{
"family_name": "Spratt",
"given_name": "Jean-Sebastien",
"clpid": "Spratt-Jean-Sebastien"
},
{
"family_name": "Rodriguez",
"given_name": "Mauro",
"orcid": "0000-0003-0545-0265",
"clpid": "Rodriguez-Mauro"
},
{
"family_name": "Schmidmayer",
"given_name": "Kevin",
"orcid": "0000-0003-0444-3098",
"clpid": "Schmidmayer-Kevin"
},
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-Spencer-H"
},
{
"family_name": "Yang",
"given_name": "Jin",
"clpid": "Yang-Jin"
},
{
"family_name": "Franck",
"given_name": "Christian",
"orcid": "0000-0002-2347-620X",
"clpid": "Franck-Christian"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Viscoelastic material properties at high strain rates are needed to model many biological and medical systems. Bubble cavitation can induce such strain rates, and the resulting bubble dynamics are sensitive to the material properties. Thus, in principle, these properties can be inferred via measurements of the bubble dynamics. Estrada et al. (2018) demonstrated such bubble-dynamic high-strain-rate rheometry by using least-squares shooting to minimize the difference between simulated and experimental bubble radius histories. We generalize their technique to account for additional uncertainties in the model, initial conditions, and material properties needed to uniquely simulate the bubble dynamics. Ensemble-based data assimilation minimizes the computational expense associated with the bubble cavitation model , providing a more efficient and scalable numerical framework for bubble-collapse rheometry. We test an ensemble Kalman filter (EnKF), an iterative ensemble Kalman smoother (IEnKS), and a hybrid ensemble-based 4D-Var method (En4D-Var) on synthetic data, assessing their estimations of the viscosity and shear modulus of a Kelvin\u2013Voigt material. Results show that En4D-Var and IEnKS provide better moduli estimates than EnKF. Applying these methods to the experimental data of Estrada et al. (2018) yields similar material property estimates to those they obtained, but provides additional information about uncertainties. In particular, the En4D-Var yields lower viscosity estimates for some experiments, and the dynamic estimators reveal a potential mechanism that is unaccounted for in the model, whereby the apparent viscosity is reduced in some cases due to inelastic behavior, possibly in the form of material damage occurring at bubble collapse.",
"doi": "10.1016/j.jmps.2021.104455",
"pmcid": "PMC8177475",
"issn": "0022-5096",
"publisher": "Elsevier",
"publication": "Journal of the Mechanics and Physics of Solids",
"publication_date": "2021-07",
"volume": "152",
"pages": "Art. No. 104455"
},
{
"id": "authors:5kc1n-vfz65",
"collection": "authors",
"collection_id": "5kc1n-vfz65",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200629-081623820",
"type": "article",
"title": "Optimal eddy viscosity for resolvent-based models of coherent structures in turbulent jets",
"author": [
{
"family_name": "Pickering",
"given_name": "Ethan",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-Ethan-M"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-Georgios"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-Oliver-T"
},
{
"family_name": "Sipp",
"given_name": "Denis",
"orcid": "0000-0002-2808-3886",
"clpid": "Sipp-Denis"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Response modes computed via linear resolvent analysis of a turbulent mean-flow field have been shown to qualitatively capture characteristics of the observed turbulent coherent structures in both wall-bounded and free shear flows. To make such resolvent models predictive, the nonlinear forcing term must be closed. Strategies to do so include imposing self-consistent sets of triadic interactions, proposing various source models or through turbulence modelling. For the latter, several investigators have proposed using the mean-field eddy viscosity acting linearly on the fluctuation field. In this study, a data-driven approach is taken to quantitatively improve linear resolvent models by deducing an optimal eddy-viscosity field that maximizes the projection of the dominant resolvent mode to the energy-optimal coherent structure educed using spectral proper orthogonal decomposition (SPOD) of data from high-fidelity simulations. We use large-eddy simulation databases for round isothermal jets at subsonic, transonic and supersonic conditions and show that the optimal eddy viscosity substantially improves the agreement between resolvent and SPOD modes, reaching over 90 % agreement at those frequencies where the jet exhibits a low-rank response. We then consider a fixed model for the eddy viscosity and show that with the calibration of a single constant, the results are generally close to the optimal one. In particular, the use of a standard Reynolds-averaged Navier\u2013Stokes eddy-viscosity resolvent model, with a single coefficient, provides substantial agreement between SPOD and resolvent modes for three turbulent jets and across the most energetic wavenumbers and frequencies.",
"doi": "10.1017/jfm.2021.232",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2021-06-25",
"volume": "917",
"pages": "Art. No. A29"
},
{
"id": "authors:1zfxp-bv622",
"collection": "authors",
"collection_id": "1zfxp-bv622",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201109-084732116",
"type": "article",
"title": "Flutter instability in an internal flow energy harvester",
"author": [
{
"family_name": "Tosi",
"given_name": "Luis Phillipe",
"orcid": "0000-0002-0819-4765",
"clpid": "Tosi-Luis-Phillipe"
},
{
"family_name": "Dorschner",
"given_name": "Benedikt",
"orcid": "0000-0001-8926-7542",
"clpid": "Dorschner-Benedikt"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Vibration-based flow energy harvesting enables robust, in situ energy extraction for low-power applications, such as distributed sensor networks. Fluid\u2013structure instabilities dictate a harvester's viability since the structural response to the flow determines its power output. Previous work on a flextensional based flow energy harvester demonstrated that an elastic member within a converging-diverging channel is susceptible to the aeroelastic flutter. This work explores the mechanism driving flutter through experiments and simulations. A model is then developed based on channel flow rate modulation and considering the effects of both normal and spanwise flow confinement on the instability. Linear stability analysis of the model replicates flutter onset, critical frequency and mode shapes observed in experiments. The model suggests that flow modulation through the channel throat is the principal mechanism for the fluid-induced vibration. The generalized model presented can serve as the foundation of design parameter exploration for energy harvesters, perhaps leading to more powerful devices in the future, but also to other similar flow geometries where the flutter instability arises in an elastic member within a narrow flow passage.",
"doi": "10.1017/jfm.2021.18",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2021-05-25",
"volume": "915",
"pages": "Art. No. A40"
},
{
"id": "authors:cp3sa-1v908",
"collection": "authors",
"collection_id": "cp3sa-1v908",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211008-183534347",
"type": "article",
"title": "A statistics-based model for cavitating polydisperse bubble clouds and their two-way-flow coupling",
"author": [
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-Spencer-H"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Phase-averaged bubbly flow models require statistical moments of the evolving bubble dynamics distributions. Under step forcing, these moments reach a statistical equilibrium in finite time. However, actual flows entail time-dependent pressure forcing and equilibrium is generally not reached. In such cases, the statistics of the evolving bubble population must be represented and evolved. Since phase-averaged models compute these moments point-wise, a low-cost algorithm for this evolution is of particular significance for large-scale simulations. We present a population-balance-based method for this purpose. The bubble dynamic coordinates are treated via a quadrature moment method and conditioned on the equilibrium bubble size. Statistics in the equilibrium bubble size coordinate are computed using a fixed quadrature rule and averaged over the period of bubble oscillation. Results show that two quadrature points in each of the bubble dynamic coordinates are sufficient to quantitatively reproduce key statistics. Further, averaging is shown to remove oscillatory behaviors that do not contribute to the moments. Together, this results in a method capable of tracking the bubble population statistics with significantly less computational expense than Monte Carlo approaches. The generality introduced by including statistics in the bubble dynamics coordinates is explored via acoustically excited bubble screen problems.",
"doi": "10.1121/10.0004431",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2021-04",
"series_number": "4",
"volume": "149",
"issue": "4",
"pages": "A29-A30"
},
{
"id": "authors:tjqwh-gvh20",
"collection": "authors",
"collection_id": "tjqwh-gvh20",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200311-160934521",
"type": "article",
"title": "Nonlinear input/output analysis: application to boundary layer transition",
"author": [
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-Georgios"
},
{
"family_name": "Sipp",
"given_name": "Denis",
"orcid": "0000-0002-2808-3886",
"clpid": "Sipp-Denis"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We extend linear input/output (resolvent) analysis to take into account nonlinear triadic interactions by considering a finite number of harmonics in the frequency domain using the harmonic balance method. Forcing mechanisms that maximise the drag are calculated using a gradient-based ascent algorithm. By including nonlinearity in the analysis, the proposed frequency-domain framework identifies the worst-case disturbances for laminar-turbulent transition. We demonstrate the framework on a flat-plate boundary layer by considering three-dimensional spanwise-periodic perturbations triggered by a few optimal forcing modes of finite amplitude. Two types of volumetric forcing are considered, one corresponding to a single frequency/spanwise wavenumber pair, and a multi-harmonic where a harmonic frequency and wavenumber are also added. Depending on the forcing strategy, we recover a range of transition scenarios associated with K-type and H-type mechanisms, including oblique and planar Tollmien\u2013Schlichting waves, streaks and their breakdown. We show that nonlinearity plays a critical role in optimising growth by combining and redistributing energy between the linear mechanisms and the higher perturbation harmonics. With a very limited range of frequencies and wavenumbers, the calculations appear to reach the early stages of the turbulent regime through the generation and breakdown of hairpin and quasi-streamwise staggered vortices.",
"doi": "10.1017/jfm.2020.982",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2021-03-25",
"volume": "911",
"pages": "Art. No. A15"
},
{
"id": "authors:vdspt-mf545",
"collection": "authors",
"collection_id": "vdspt-mf545",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210122-092028610",
"type": "article",
"title": "Acoustic cavitation rheometry",
"author": [
{
"family_name": "Mancia",
"given_name": "Lauren",
"orcid": "0000-0003-4366-1944",
"clpid": "Mancia-Lauren"
},
{
"family_name": "Yang",
"given_name": "Jin",
"clpid": "Yang-Jin"
},
{
"family_name": "Spratt",
"given_name": "Jean-Sebastien",
"clpid": "Spratt-Jean-Sebastien"
},
{
"family_name": "Sukovich",
"given_name": "Jonathan R.",
"orcid": "0000-0002-5650-991X",
"clpid": "Sukovich-Jonathan-R"
},
{
"family_name": "Xu",
"given_name": "Zhen",
"clpid": "Xu-Zhen"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Franck",
"given_name": "Christian",
"orcid": "0000-0002-2347-620X",
"clpid": "Franck-Christian"
},
{
"family_name": "Johnsen",
"given_name": "Eric",
"orcid": "0000-0001-9530-408X",
"clpid": "Johnsen-Eric"
}
],
"abstract": "Characterization of soft materials is challenging due to their high compliance and the strain-rate dependence of their mechanical properties. The inertial microcavitation-based high strain-rate rheometry (IMR) method [Estrada et al., J. Mech. Phys. Solids, 2018, 112, 291\u2013317] combines laser-induced cavitation measurements with a model for the bubble dynamics to measure local properties of polyacrylamide hydrogel under high strain-rates from 10\u00b3 to 10\u2078 s\u207b\u00b9. While promising, laser-induced cavitation involves plasma formation and optical breakdown during nucleation, a process that could alter local material properties before measurements are obtained. In the present study, we extend the IMR method to another means to generate cavitation, namely high-amplitude focused ultrasound, and apply the resulting acoustic-cavitation-based IMR to characterize the mechanical properties of agarose hydrogels. Material properties including viscosity, elastic constants, and a stress-free bubble radius are inferred from bubble radius histories in 0.3% and 1% agarose gels. An ensemble-based data assimilation is used to further help interpret the obtained estimates. The resulting parameter distributions are consistent with available measurements of agarose gel properties and with expected trends related to gel concentration and high strain-rate loading. Our findings demonstrate the utility of applying IMR and data assimilation methods with single-bubble acoustic cavitation data for measurement of viscoelastic properties.",
"doi": "10.1039/d0sm02086a",
"issn": "1744-683X",
"publisher": "Royal Society of Chemistry",
"publication": "Soft Matter",
"publication_date": "2021-03-14",
"series_number": "10",
"volume": "17",
"issue": "10",
"pages": "2931-2941"
},
{
"id": "authors:ywh7t-5ha37",
"collection": "authors",
"collection_id": "ywh7t-5ha37",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200624-090733478",
"type": "article",
"title": "Dynamics of an inverted cantilever plate at moderate angle of attack",
"author": [
{
"family_name": "Huertas-Cerdeira",
"given_name": "Cecilia",
"orcid": "0000-0003-4553-0470",
"clpid": "Huertas-Cerdeira-Cecilia"
},
{
"family_name": "Goza",
"given_name": "Andres",
"orcid": "0000-0002-9372-7713",
"clpid": "Goza-Andres"
},
{
"family_name": "Sader",
"given_name": "John E.",
"orcid": "0000-0002-7096-0627",
"clpid": "Sader-John-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Gharib",
"given_name": "Morteza",
"orcid": "0000-0003-0754-4193",
"clpid": "Gharib-M"
}
],
"abstract": "The dynamics of a cantilever plate clamped at its trailing edge and placed at a moderate angle (\u03b1\u226430\u2218) to a uniform flow are investigated experimentally and numerically, and a large experimental data set is provided. The dynamics are shown to differ significantly from the zero-angle-of-attack case, commonly called the inverted-flag configuration. Four distinct dynamical regimes arise at non-zero angles: a small oscillation around a small-deflection equilibrium (deformed regime), a small-amplitude flapping motion, a large-amplitude flapping motion and a small oscillation around a large-deflection equilibrium (deflected regime). The small- and large-amplitude flapping motions are shown to be produced by different physical mechanisms. The small-amplitude flapping motion appears gradually as the flow speed is increased and is consistent with a limit-cycle oscillation caused by the quasi-steady fluid forcing. The large-amplitude flapping motion is observed to appear at a constant critical flow speed that is independent of angle of attack. Its characteristics match those of the large-amplitude vortex-induced vibration present at zero angle of attack. The flow speed at which the plate enters the deflected regime decreases linearly as the angle of attack is increased, causing the flapping motion to disappear for angles of attack greater than \u03b1\u224828\u2218. Finally, the effect of aspect ratio on the plate dynamics is considered, with a plate of reduced aspect ratio being shown to lack a sharp distinction between flapping regimes for \u03b1>8\u2218.",
"doi": "10.1017/jfm.2020.922",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2021-02-25",
"volume": "909",
"pages": "Art. No. A20"
},
{
"id": "authors:fca3f-yfd90",
"collection": "authors",
"collection_id": "fca3f-yfd90",
"cite_using_url": "https://authors.library.caltech.edu/records/fca3f-yfd90",
"type": "article",
"title": "Dynamics of an inverted cantilever plate at moderate angle of attack",
"author": [
{
"family_name": "Huertas-Cerdeira",
"given_name": "Cecilia",
"orcid": "0000-0003-4553-0470",
"clpid": "Huertas-Cerdeira-Cecilia"
},
{
"family_name": "Goza",
"given_name": "Andres",
"orcid": "0000-0002-9372-7713",
"clpid": "Goza-Andres"
},
{
"family_name": "Sader",
"given_name": "John E.",
"orcid": "0000-0002-7096-0627",
"clpid": "Sader-J-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Gharib",
"given_name": "Morteza",
"orcid": "0000-0003-0754-4193",
"clpid": "Gharib-M"
}
],
"abstract": "The dynamics of a cantilever plate clamped at its trailing edge and placed at a moderate angle ((\u03b1 \u2264 30\u00b0) to a uniform flow are investigated experimentally and numerically, and a large experimental data set is provided. The dynamics are shown to differ significantly from the zero-angle-of-attack case, commonly called the inverted-flag configuration. Four distinct dynamical regimes arise at non-zero angles: a small oscillation around a small-deflection equilibrium (deformed regime), a small-amplitude flapping motion, a large-amplitude flapping motion and a small oscillation around a large-deflection equilibrium (deflected regime). The small- and large-amplitude flapping motions are shown to be produced by different physical mechanisms. The small-amplitude flapping motion appears gradually as the flow speed is increased and is consistent with a limit-cycle oscillation caused by the quasi-steady fluid forcing. The large-amplitude flapping motion is observed to appear at a constant critical flow speed that is independent of angle of attack. Its characteristics match those of the large-amplitude vortex-induced vibration present at zero angle of attack. The flow speed at which the plate enters the deflected regime decreases linearly as the angle of attack is increased, causing the flapping motion to disappear for angles of attack greater than \u03b1 \u2248 28\u00b0. Finally, the effect of aspect ratio on the plate dynamics is considered, with a plate of reduced aspect ratio being shown to lack a sharp distinction between flapping regimes for \u03b1 > 8\u00b0.
",
"doi": "10.1017/jfm.2020.922",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2021-02-25",
"volume": "909",
"pages": "A20"
},
{
"id": "authors:077rb-xv855",
"collection": "authors",
"collection_id": "077rb-xv855",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201208-105036247",
"type": "article",
"title": "Amplitude Scaling of Wave Packets in Turbulent Jets",
"author": [
{
"family_name": "Antonialli",
"given_name": "Luigi A.",
"clpid": "Antonialli-Luigi-A"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-Andr\u00e9-V-G"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-Oliver-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-Peter"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-Aaron"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-Guillaume-A"
}
],
"abstract": "This paper studies the amplitude of large-scale coherent wave-packet structures in jets, modeled by the parabolized stability equations (PSEs). Linear PSEs can retrieve the shape of the wave packets, but linearity leads to solutions with a free amplitude, which has traditionally been obtained in an ad hoc manner using limited data. We systematically determine the free amplitude as a function of frequency and azimuthal wave number by comparing the fluctuation fields retrieved from PSEs with coherent structures educed from large-eddy simulation data using spectral proper orthogonal decomposition. The wave-packet amplitude is shown to decay exponentially with the Strouhal number for axisymmetric and helical modes at both Mach numbers considered in the study: 0.4 and 0.9. Analytical fit functions are proposed, and the scaled wave packets provide reasonable reconstructions of pressure and velocity spectra on the jet centerline and lip line over a range of streamwise positions.",
"doi": "10.2514/1.j059599",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2021-02",
"series_number": "2",
"volume": "59",
"issue": "2",
"pages": "559-568"
},
{
"id": "authors:8jfq2-gvg19",
"collection": "authors",
"collection_id": "8jfq2-gvg19",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201012-140154360",
"type": "article",
"title": "Dynamics and decay of a spherical region of turbulence in free space",
"author": [
{
"family_name": "Yu",
"given_name": "Ke",
"orcid": "0000-0003-0157-4471",
"clpid": "Yu-Ke"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Pullin",
"given_name": "D. I.",
"orcid": "0009-0007-5991-2863",
"clpid": "Pullin-D-I"
},
{
"family_name": "Winckelmans",
"given_name": "Gr\u00e9goire",
"clpid": "Winckelmans-Gr\u00e9goire"
}
],
"abstract": "We perform direct numerical simulation and large-eddy simulation of an initially spherical region of turbulence evolving in free space. The computations are performed with a lattice Green's function method, which allows the exact free-space boundary conditions to be imposed on a compact vortical region. Large-eddy simulations are conducted with the stretched vortex subgrid stress model. The initial condition is spherically windowed, isotropic homogeneous incompressible turbulence. We study the spectrum and statistics of the decaying turbulence and compare the results with decaying isotropic turbulence, including cases representing different low-wavenumber behaviour of the energy spectrum (i.e. k\u00b2 versus k\u2074). At late times the turbulent sphere expands with both mean radius and integral scale showing similar timewise growth exponents. The low-wavenumber behaviour has little effect on the inertial scales, and we find that decay rates follow the predictions of Saffman (J. Fluid Mech., vol. 27, 1967, pp. 581\u2013593) in both cases, at least until approximately 400 initial eddy turnover times. The boundary of the spherical region develops intermittency and features ejections of vortex rings. These are shown to occur at the integral scale of the initial turbulence field and are hypothesized to occur due to a local imbalance of impulse on this scale.",
"doi": "10.1017/jfm.2020.818",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2021-01-25",
"volume": "907",
"pages": "Art. No. A19"
},
{
"id": "authors:wpr22-d0e16",
"collection": "authors",
"collection_id": "wpr22-d0e16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20210121-111627081",
"type": "article",
"title": "Lift coefficient estimation for a rapidly pitching airfoil",
"author": [
{
"family_name": "An",
"given_name": "Xuanhong",
"orcid": "0000-0001-6950-2867",
"clpid": "An-Xuanhong"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-David-R"
},
{
"family_name": "Eldredge",
"given_name": "Jeff D.",
"orcid": "0000-0002-2672-706X",
"clpid": "Eldredge-Jeff-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We develop a method for estimating the instantaneous lift coefficient on a rapidly pitching airfoil that uses a small number of pressure sensors and a measurement of the angle of attack. The approach assimilates four surface pressure measurements with a modified nonlinear state space model (Goman\u2013Khrabrov model) through a Kalman filter. The error of lift coefficient estimates based only on a weighted-sum of the measured pressures are found to be noisy and biased, which leads to inaccurate estimates. The estimate is improved by including the predictive model in an conventional Kalman filter. The Goman\u2013Khrabrov model is shown to be a linear parameter-varying system and can therefore be used in the Kalman filter without the need for linearization. Additional improvement is realized by modifying the algorithm to provide more accurate estimate of the lift coefficient. The improved Kalman filtering approach results in a bias-free lift coefficient estimate that is more precise than either the pressure-based estimate or the Goman\u2013Khrabrov model on their own. The new method will enable performance enhancements in aerodynamic systems whose performance relies on lift.",
"doi": "10.1007/s00348-020-03105-3",
"issn": "0723-4864",
"publisher": "Springer",
"publication": "Experiments in Fluids",
"publication_date": "2021-01",
"series_number": "1",
"volume": "62",
"issue": "1",
"pages": "Art. No. 11"
},
{
"id": "authors:f037h-p8n15",
"collection": "authors",
"collection_id": "f037h-p8n15",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200427-080644291",
"type": "article",
"title": "On the formation and recurrent shedding of ligaments in droplet aerobreakup",
"author": [
{
"family_name": "Dorschner",
"given_name": "Benedikt",
"orcid": "0000-0001-8926-7542",
"clpid": "Dorschner-Benedikt"
},
{
"family_name": "Biasiori-Poulanges",
"given_name": "Luc",
"clpid": "Biasiori-Poulanges-Luc"
},
{
"family_name": "Schmidmayer",
"given_name": "Kevin",
"orcid": "0000-0003-0444-3098",
"clpid": "Schmidmayer-Kevin"
},
{
"family_name": "El-Rabii",
"given_name": "Hazem",
"clpid": "El-Rabii-Hazem"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The breakup of water droplets when exposed to high-speed gas flows is investigated using both high-magnification shadowgraphy experiments as well as fully three-dimensional numerical simulations, which account for viscous as well as capillary effects. After thorough validation of the simulations with respect to the experiments, we elucidate the ligament formation process and the effect of surface tension. By Fourier decomposition of the flow field, we observe the development of specific azimuthal modes, which destabilize the liquid sheet surrounding the droplet. Eventually, the liquid sheet is ruptured, which leads to the formation of ligaments. We further observe the ligament formation and shedding to be a recurrent process. While the first ligament shedding weakly depends on the Weber number, subsequent shedding processes seem to be driven primarily by inertia and the vortex shedding in the wake of the deformed droplet.",
"doi": "10.1017/jfm.2020.699",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2020-12-10",
"volume": "904",
"pages": "Art. No. A20"
},
{
"id": "authors:7tj86-asp68",
"collection": "authors",
"collection_id": "7tj86-asp68",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200824-094426276",
"type": "article",
"title": "Ambiguity in mean-flow-based linear analysis",
"author": [
{
"family_name": "Karban",
"given_name": "U.",
"orcid": "0000-0003-0803-0581",
"clpid": "Karban-U"
},
{
"family_name": "Bugeat",
"given_name": "B.",
"clpid": "Bugeat-B"
},
{
"family_name": "Martini",
"given_name": "E.",
"orcid": "0000-0002-3144-5702",
"clpid": "Martini-E"
},
{
"family_name": "Towne",
"given_name": "A.",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Cavalieri",
"given_name": "A. V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Lesshafft",
"given_name": "L.",
"orcid": "0000-0002-2513-4553",
"clpid": "Lesshafft-L"
},
{
"family_name": "Agarwal",
"given_name": "A.",
"clpid": "Agarwal-A"
},
{
"family_name": "Jordan",
"given_name": "P.",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Linearisation of the Navier\u2013Stokes equations about the mean of a turbulent flow forms the foundation of popular models for energy amplification and coherent structures, including resolvent analysis. While the Navier\u2013Stokes equations can be equivalently written using many different sets of dependent variables, we show that the properties of the linear operator obtained via linearisation about the mean depend on the variables in which the equations are written prior to linearisation, and can be modified under nonlinear transformation of variables. For example, we show that using primitive and conservative variables leads to differences in the singular values and modes of the resolvent operator for turbulent jets, and that the differences become more severe as variable-density effects increase. This lack of uniqueness of mean-flow-based linear analysis provides new opportunities for optimising models by specific choice of variables while also highlighting the importance of carefully accounting for the nonlinear terms that act as a forcing on the resolvent operator.",
"doi": "10.1017/jfm.2020.566",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2020-10-10",
"volume": "900",
"pages": "Art. No. R5"
},
{
"id": "authors:dzmnz-gsg42",
"collection": "authors",
"collection_id": "dzmnz-gsg42",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200806-103840041",
"type": "article",
"title": "Near-surface dynamics of a gas bubble collapsing above a crevice",
"author": [
{
"family_name": "Trummler",
"given_name": "Theresa",
"orcid": "0000-0001-8869-5860",
"clpid": "Trummler-Theresa"
},
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-S-H"
},
{
"family_name": "Schmidmayer",
"given_name": "Kevin",
"orcid": "0000-0003-0444-3098",
"clpid": "Schmidmayer-Kevin"
},
{
"family_name": "Schmidt",
"given_name": "Steffen J.",
"orcid": "0000-0001-6661-4505",
"clpid": "Schmidt-S-J"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Adams",
"given_name": "Nikolaus A.",
"orcid": "0000-0001-5048-8639",
"clpid": "Adams-N-A"
}
],
"abstract": "The impact of a collapsing gas bubble above rigid, notched walls is considered. Such surface crevices and imperfections often function as bubble nucleation sites, and thus have a direct relation to cavitation-induced erosion and damage structures. A generic configuration is investigated numerically using a second-order accurate compressible multi-component flow solver in a two-dimensional axisymmetric coordinate system. Results show that the crevice geometry has a significant effect on the collapse dynamics, jet formation, subsequent wave dynamics and interactions. The wall-pressure distribution associated with erosion potential is a direct consequence of development and intensity of these flow phenomena.",
"doi": "10.1017/jfm.2020.432",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2020-09-25",
"volume": "899",
"pages": "Art. No. A16"
},
{
"id": "authors:rmv2k-2nx60",
"collection": "authors",
"collection_id": "rmv2k-2nx60",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200122-091643948",
"type": "article",
"title": "Lift-up, Kelvin-Helmholtz and Orr mechanisms in turbulent jets",
"author": [
{
"family_name": "Pickering",
"given_name": "Ethan",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-E-M"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-G"
},
{
"family_name": "Nogueira",
"given_name": "Petr\u00f4nio A. S.",
"clpid": "Nogueira-P-A"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Three amplification mechanisms present in turbulent jets, namely lift-up, Kelvin\u2013Helmholtz and Orr, are characterized via global resolvent analysis and spectral proper orthogonal decomposition (SPOD) over a range of Mach numbers. The lift-up mechanism was recently identified in turbulent jets via local analysis by Nogueira et al. (J. Fluid Mech., vol. 873, 2019, pp. 211\u2013237) at low Strouhal number ( St ) and non-zero azimuthal wavenumbers ( m ). In these limits, a global SPOD analysis of data from high-fidelity simulations reveals streamwise vortices and streaks similar to those found in turbulent wall-bounded flows. These structures are in qualitative agreement with the global resolvent analysis, which shows that they are a response to upstream forcing of streamwise vorticity near the nozzle exit. Analysis of mode shapes, component-wise amplitudes and sensitivity analysis distinguishes the three mechanisms and the regions of frequency\u2013wavenumber space where each dominates, finding lift-up to be dominant as St/m\u21920 . Finally, SPOD and resolvent analyses of localized regions show that the lift-up mechanism is present throughout the jet, with a dominant azimuthal wavenumber inversely proportional to streamwise distance from the nozzle, with streaks of azimuthal wavenumber exceeding five near the nozzle, and wavenumbers one and two most energetic far downstream of the potential core.",
"doi": "10.1017/jfm.2020.301",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2020-08-10",
"volume": "896",
"pages": "Art. No. A2"
},
{
"id": "authors:1xdr6-8n320",
"collection": "authors",
"collection_id": "1xdr6-8n320",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200526-131556031",
"type": "article",
"title": "Enhancement of shock-capturing methods via machine learning",
"author": [
{
"family_name": "Stevens",
"given_name": "Ben",
"orcid": "0000-0002-3410-5922",
"clpid": "Stevens-Ben"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "In recent years, machine learning has been used to create data-driven solutions to problems for which an algorithmic solution is intractable, as well as fine-tuning existing algorithms. This research applies machine learning to the development of an improved finite-volume method for simulating PDEs with discontinuous solutions. Shock-capturing methods make use of nonlinear switching functions that are not guaranteed to be optimal. Because data can be used to learn nonlinear relationships, we train a neural network to improve the results of a fifth-order WENO method. We post-process the outputs of the neural network to guarantee that the method is consistent. The training data consist of the exact mapping between cell averages and interpolated values for a set of integrable functions that represent waveforms we would expect to see while simulating a PDE. We demonstrate our method on linear advection of a discontinuous function, the inviscid Burgers' equation, and the 1-D Euler equations. For the latter, we examine the Shu\u2013Osher model problem for turbulence\u2013shock wave interactions. We find that our method outperforms WENO in simulations where the numerical solution becomes overly diffused due to numerical viscosity.",
"doi": "10.1007/s00162-020-00531-1",
"issn": "0935-4964",
"publisher": "Springer",
"publication": "Theoretical and Computational Fluid Dynamics",
"publication_date": "2020-08",
"series_number": "4",
"volume": "34",
"issue": "4",
"pages": "483-496"
},
{
"id": "authors:m4p5z-40g24",
"collection": "authors",
"collection_id": "m4p5z-40g24",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211008-225804351",
"type": "patent",
"title": "Tracheotomy device",
"author": [
{
"family_name": "Wilson",
"given_name": "Byron",
"clpid": "Wilson-Byron"
},
{
"family_name": "Yen",
"given_name": "Harrison",
"clpid": "Yen-Harrison"
},
{
"family_name": "Young",
"given_name": "Ethan",
"clpid": "Young-Ethan"
},
{
"family_name": "Eldredge",
"given_name": "Jeff D.",
"orcid": "0000-0002-2672-706X",
"clpid": "Eldredge-Jeff-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "An aspect of the disclosure is related to a medical device for providing an air passageway through a neck of a patient. In one embodiment, the medical device may include: a neckband configured to extend around the neck of the patient, the neckband including a connector positioned along a length of the neckband for positioning along an anterior part of the neck of the patient, the connector including a connector through hole; a cannula having an elongated tube extending from a connecting head, the elongated tube being configured to extend into a trachea of the patient and including an inner passageway, the connecting head having a through hole that is continuous with the inner passageway of the elongated tube thereby allowing air to pass through the cannula into the trachea, the connecting head having an outer diameter that is sized to have a friction fit with the connector through hole.",
"publisher": "U.S. Patent Office",
"publication_date": "2020-07-16"
},
{
"id": "authors:ewgen-srj21",
"collection": "authors",
"collection_id": "ewgen-srj21",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200918-102621101",
"type": "article",
"title": "QBMMlib: A library of quadrature-based moment methods",
"author": [
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-Spencer-H"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Fox",
"given_name": "Rodney O.",
"orcid": "0000-0003-1944-1861",
"clpid": "Fox-Rodney-O"
}
],
"abstract": "QBMMlib is an open source package of quadrature-based moment methods and their algorithms. Such methods are commonly used to solve fully-coupled disperse flow and combustion problems, though formulating and closing the corresponding governing equations can be complex. QBMMlib aims to make analyzing these techniques simple and more accessible. Its routines use symbolic manipulation to formulate the moment transport equations for a population balance equation and a prescribed dynamical system. The resulting moment transport equations are closed by first trading the moments for a set of quadrature points and weights via an inversion algorithm, of which several are available. Quadratures then compute the moments required for closure. Embedded code snippets show how to use QBMMlib, with the algorithm initialization and solution spanning just 13 total lines of code. Examples are shown and analyzed for a linear harmonic oscillator and a bubble dynamics problem.",
"doi": "10.1016/j.softx.2020.100615",
"issn": "2352-7110",
"publisher": "Elsevier",
"publication": "SoftwareX",
"publication_date": "2020-07",
"volume": "12",
"pages": "Art. No. 100615"
},
{
"id": "authors:7e8pm-sw309",
"collection": "authors",
"collection_id": "7e8pm-sw309",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211008-210432471",
"type": "book_section",
"title": "Application of the One-Way Navier-Stokes (OWNS) Equations to Hypersonic Boundary Layers",
"book_title": "AIAA AVIATION 2020 FORUM",
"author": [
{
"family_name": "Kamal",
"given_name": "Omar",
"clpid": "Kamal-Omar"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-Georgios"
},
{
"family_name": "Lakebrink",
"given_name": "Matthew T.",
"clpid": "Lakebrink-Matthew-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Prediction of linear amplification of disturbances in hypersonic boundary layers is challenging due to the presence and interactions of discrete modes (e.g. Tollmien-Schlichting and Mack) and continuous modes (entropic, vortical, and acoustic). While DNS and global analysis can be used, the large grids required make the computation of optimal transient and forced responses expensive, particularly when a large parameter space is required. At the same time, parabolized stability equations are non-convergent and unreliable for problems involving multi-modal and non-modal interactions. In this work, we apply the One-Way Navier-Stokes (OWNS) equations to hypersonic boundary layers. OWNS is based on a rigorous, approximate parabolization of the equations of motion that removes disturbances with upstream group velocity using a high-order recursive filter. We extend the original algorithm by considering non-orthogonal body-fitted curvilinear coordinates and incorporate full compressibility with temperature-dependent fluid properties. We validate the results by comparing to DNS data for a flat plate and sharp cone, and to LST results for local disturbances on the centerline of the HIFiRE-5 elliptic cone. OWNS provides DNS-quality results for the former flows at a small fraction of the computational expense.",
"doi": "10.2514/6.2020-2986",
"isbn": "978-1-62410-598-2",
"publisher": "American Institute of Aeronautics and Astronautics",
"place_of_publication": "Reston, VA",
"publication_date": "2020-06",
"pages": "Art. No. 2020-2986"
},
{
"id": "authors:5cahp-55q16",
"collection": "authors",
"collection_id": "5cahp-55q16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200309-084519190",
"type": "article",
"title": "A Gaussian moment method and its augmentation via LSTM recurrent neural networks for the statistics of cavitating bubble populations",
"author": [
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265"
},
{
"family_name": "Charalampopoulos",
"given_name": "Alexis"
},
{
"family_name": "Sapsis",
"given_name": "Themistoklis P."
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Phase-averaged dilute bubbly flow models require high-order statistical moments of the bubble population. The method of classes, which directly evolve bins of bubbles in the probability space, are accurate but computationally expensive. Moment-based methods based upon a Gaussian closure present an opportunity to accelerate this approach, particularly when the bubble size distributions are broad (polydisperse). For linear bubble dynamics a Gaussian closure is exact, but for bubbles undergoing large and nonlinear oscillations, it results in a large error from misrepresented higher-order moments. Long short-term memory recurrent neural networks, trained on Monte Carlo truth data, are proposed to improve these model predictions. The networks are used to correct the low-order moment evolution equations and improve prediction of higher-order moments based upon the low-order ones. Results show that the networks can reduce model errors to less than 1% of their unaugmented values.",
"doi": "10.1016/j.ijmultiphaseflow.2020.103262",
"issn": "0301-9322",
"publisher": "Elsevier",
"publication": "International Journal of Multiphase Flow",
"publication_date": "2020-06",
"volume": "127",
"pages": "Art. No. 103262"
},
{
"id": "authors:semrs-rcz98",
"collection": "authors",
"collection_id": "semrs-rcz98",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200415-094204836",
"type": "article",
"title": "Role of Coherent Structures in Turbulent Premixed Flame Acoustics",
"author": [
{
"family_name": "Brouzet",
"given_name": "D.",
"clpid": "Brouzet-D"
},
{
"family_name": "Haghiri",
"given_name": "A.",
"clpid": "Haghiri-A"
},
{
"family_name": "Talei",
"given_name": "M.",
"clpid": "Talei-M"
},
{
"family_name": "Brear",
"given_name": "M. J.",
"clpid": "Brear-M-J"
},
{
"family_name": "Schmidt",
"given_name": "O. T.",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Rigas",
"given_name": "G.",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-G"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Spectral proper orthogonal decomposition (SPOD) is applied to direct numerical simulation datasets of a lean and a stoichiometric methane\u2013air turbulent premixed jet flame. SPOD is used to extract the coherent structures that correlate with the radiated sound by using an inner product based on a linearized disturbance energy. Two types of structures are prominent in the data. The first type arises in the jet's shear layer and is linked to the Kelvin\u2013Helmholtz instability, which is an important mechanism of sound generation in nonreacting jets. These structures produce sound through deformation of the flame front in the shear layer. They contain most of the acoustic energy and are dominant at Strouhal numbers (defined based on the jet's diameter and the inlet mean velocity) less than unity. The second type of structures is found near the jet centerline, where large fluctuations of the flame surface are observed. The structures are linked to small nonlinear flame dynamics and to the Orr mechanism. They travel at a speed close to the inlet mean velocity and are important at higher Strouhal numbers. Regardless of their energy content, both types of structures have important contributions to the broadband nature of combustion noise.",
"doi": "10.2514/1.j058480",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2020-06",
"series_number": "6",
"volume": "58",
"issue": "6",
"pages": "2635-2642"
},
{
"id": "authors:wt2zm-26216",
"collection": "authors",
"collection_id": "wt2zm-26216",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200518-095000249",
"type": "book_section",
"title": "Immersed Boundary Projection Methods",
"book_title": "Immersed Boundary Method: Development and Applications",
"author": [
{
"family_name": "Dorschner",
"given_name": "Benedikt",
"orcid": "0000-0001-8926-7542",
"clpid": "Dorschner-Benedikt"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "Roy",
"given_name": "Somnath",
"clpid": "Roy-Somnath"
},
{
"family_name": "De",
"given_name": "Ashoke",
"clpid": "De-Ashoke"
},
{
"family_name": "Balaras",
"given_name": "Elias",
"clpid": "Balaras-E"
}
],
"abstract": "Immersed boundary methods are an attractive alternative to body-fitted grids for complex geometries and fluid\u2013structure interaction problems. The simplicity of the underlying Cartesian mesh allows for a number of useful conservation and stability properties to be embedded in the numerics, and for the resulting discrete equations to be solved efficiently and scalably. We review the immersed boundary projection method for incompressible flows, which implicitly satisfies the no-slip condition at immersed surfaces by solving a system of algebraic equations for surface traction. We discuss issues related to the smoothness of the surface stresses and solution strategies for strongly coupled fluid\u2013structure interaction. For three-dimensional flows on unbounded domains, we discuss a fast lattice Green's function method that provides for an adaptive domain comprising the vortical flow region and at the same time can be solved efficiently using extensions of the fast multipole method. To illustrate the methods, we present a series of benchmark simulations in two and three dimensions, ranging from inverted flag flutter, flow past spinning and inclined disks, and turbulent flow past a sphere.",
"doi": "10.1007/978-981-15-3940-4_1",
"isbn": "978-981-15-3939-8",
"publisher": "Springer",
"place_of_publication": "Singapore",
"publication_date": "2020-05-16",
"pages": "3-43"
},
{
"id": "authors:ef77k-ja894",
"collection": "authors",
"collection_id": "ef77k-ja894",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200423-103521218",
"type": "article",
"title": "Flow state estimation in the presence of discretization errors",
"author": [
{
"family_name": "da\u00a0Silva",
"given_name": "Andre F. C.",
"orcid": "0000-0002-8125-6010",
"clpid": "da-Silva-A-F-C"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Ensemble data assimilation methods integrate measurement data and computational flow models to estimate the state of fluid systems in a robust, scalable way. However, discretization errors in the dynamical and observation models lead to biased forecasts and poor estimator performance. We propose a low-rank representation for this bias, whose dynamics is modelled by data-informed, time-correlated processes. State and bias parameters are simultaneously corrected online with the ensemble Kalman filter. The proposed methodology is then applied to the problem of estimating the state of a two-dimensional flow at modest Reynolds number using an ensemble of coarse-mesh simulations and pressure measurements at the surface of an immersed body in a synthetic experiment framework. Using an ensemble size of 60, the bias-aware estimator is demonstrated to achieve at least 70 % error reduction when compared to its bias-blind counterpart. Strategies to determine the bias statistics and their impact on the estimator performance are discussed.",
"doi": "10.1017/jfm.2020.103",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2020-05-10",
"volume": "890",
"pages": "Art. No. A10"
},
{
"id": "authors:zw96b-4v596",
"collection": "authors",
"collection_id": "zw96b-4v596",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20191223-155123107",
"type": "article",
"title": "A fast multi-resolution lattice Green's function method for elliptic difference equations",
"author": [
{
"family_name": "Dorschner",
"given_name": "Benedikt",
"orcid": "0000-0001-8926-7542",
"clpid": "Dorschner-Benedikt"
},
{
"family_name": "Yu",
"given_name": "Ke",
"orcid": "0000-0003-0157-4471",
"clpid": "Yu-Ke"
},
{
"family_name": "Mengaldo",
"given_name": "Gianmarco",
"orcid": "0000-0002-0157-5477",
"clpid": "Mengaldo-Gianmarco"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We propose a mesh refinement technique for solving elliptic difference equations on unbounded domains based on the fast lattice Green's function (FLGF) method. The FLGF method exploits the regularity of the Cartesian mesh and uses the fast multipole method in conjunction with fast Fourier transforms to yield linear complexity and decrease time-to-solution. We extend this method to a multi-resolution scheme and allow for locally refined Cartesian blocks embedded in the computational domain. Appropriately chosen interpolation and regularization operators retain consistency between the discrete Laplace operator and its inverse on the unbounded domain. Second-order accuracy and linear complexity are maintained, while significantly reducing the number of degrees of freedom and hence the computational cost.",
"doi": "10.1016/j.jcp.2020.109270",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2020-04-15",
"volume": "407",
"pages": "Art. No. 109270"
},
{
"id": "authors:gcvbg-5ks79",
"collection": "authors",
"collection_id": "gcvbg-5ks79",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200306-133727805",
"type": "article",
"title": "Guide to Spectral Proper Orthogonal Decomposition",
"author": [
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "This paper discusses the spectral proper orthogonal decomposition and its use in identifying modes, or structures, in flow data. A specific algorithm based on estimating the cross-spectral density tensor with Welch's method is presented, and guidance is provided on selecting data sampling parameters and understanding tradeoffs among them in terms of bias, variability, aliasing, and leakage. Practical implementation issues, including dealing with large datasets, are discussed and illustrated with examples involving experimental and computational turbulent flow data.",
"doi": "10.2514/1.j058809",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2020-03",
"series_number": "3",
"volume": "58",
"issue": "3",
"pages": "1023-1033"
},
{
"id": "authors:sfjhs-2hy96",
"collection": "authors",
"collection_id": "sfjhs-2hy96",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211008-205456499",
"type": "monograph",
"title": "FiniteNet: A Fully Convolutional LSTM Network Architecture for Time-Dependent Partial Differential Equations",
"author": [
{
"family_name": "Stevens",
"given_name": "Ben",
"orcid": "0000-0002-3410-5922",
"clpid": "Stevens-Ben"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "In this work, we present a machine learning approach for reducing the error when numerically solving time-dependent partial differential equations (PDE). We use a fully convolutional LSTM network to exploit the spatiotemporal dynamics of PDEs. The neural network serves to enhance finite-difference and finite-volume methods (FDM/FVM) that are commonly used to solve PDEs, allowing us to maintain guarantees on the order of convergence of our method. We train the network on simulation data, and show that our network can reduce error by a factor of 2 to 3 compared to the baseline algorithms. We demonstrate our method on three PDEs that each feature qualitatively different dynamics. We look at the linear advection equation, which propagates its initial conditions at a constant speed, the inviscid Burgers' equation, which develops shockwaves, and the Kuramoto-Sivashinsky (KS) equation, which is chaotic.",
"doi": "10.48550/arXiv.2002.03014",
"publisher": "arXiv",
"publication_date": "2020-02-07"
},
{
"id": "authors:ns24x-nsz38",
"collection": "authors",
"collection_id": "ns24x-nsz38",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190513-102413759",
"type": "article",
"title": "An assessment of multicomponent flow models and interface capturing schemes for spherical bubble dynamics",
"author": [
{
"family_name": "Schmidmayer",
"given_name": "Kevin",
"orcid": "0000-0003-0444-3098",
"clpid": "Schmidmayer-Kevin"
},
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-S-H"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Numerical simulation of bubble dynamics and cavitation is challenging; even the seemingly simple problem of a collapsing spherical bubble is difficult to compute accurately with a general, three-dimensional, compressible, multicomponent flow solver. Difficulties arise due to both the physical model and the numerical method chosen for its solution. We consider the 5-equation model of Allaire et al. [1], the 5-equation model of Kapila et al. [2], and the 6-equation model of Saurel et al. [3] as candidate approaches for spherical bubble dynamics, and both MUSCL and WENO interface-capturing methods are implemented and compared. We demonstrate the inadequacy of the traditional 5-equation model of Allaire et al. [1] for spherical bubble collapse problems and explain the corresponding advantages of the augmented model of Kapila et al. [2] for representing this phenomenon. Quantitative comparisons between the augmented 5-equation and 6-equation models for three-dimensional bubble collapse problems demonstrate the versatility of pressure-disequilibrium models. Lastly, the performance of pressure disequilibrium model for representing a three-dimensional spherical bubble collapse for different bubble interior/exterior pressure ratios is evaluated for different numerical methods. Pathologies associated with each factor and their origins are identified and discussed.",
"doi": "10.1016/j.jcp.2019.109080",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2020-02-01",
"volume": "402",
"pages": "Art. No. 109080"
},
{
"id": "authors:98kt9-p2247",
"collection": "authors",
"collection_id": "98kt9-p2247",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20191216-160711298",
"type": "article",
"title": "Simulation of humpback whale bubble-net feeding models",
"author": [
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-S-H"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Humpback whales can generate intricate bubbly regions, called bubble nets, via blowholes. Humpback whales appear to exploit these bubble nets for feeding via loud vocalizations. A fully-coupled phase-averaging approach is used to model the flow, bubble dynamics, and corresponding acoustics. A previously hypothesized waveguiding mechanism is assessed for varying acoustic frequencies and net void fractions. Reflections within the bubbly region result in observable waveguiding for only a small range of flow parameters. A configuration of multiple whales surrounding and vocalizing towards an annular bubble net is also analyzed. For a range of flow parameters, the bubble net keeps its core region substantially quieter than the exterior. This approach appears more viable, though it relies upon the cooperation of multiple whales. A spiral bubble net configuration that circumvents this requirement is also investigated. The acoustic wave behaviors in the spiral interior vary qualitatively with the vocalization frequency and net void fraction. The competing effects of vocalization guiding and acoustic attenuation are quantified. Low void fraction cases allow low-frequency waves to partially escape the spiral region, with the remaining vocalizations still exciting the net interior. Higher void fraction nets appear preferable, guiding even low-frequency vocalizations while still maintaining a quiet net interior.",
"doi": "10.1121/10.0000746",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2020-02",
"series_number": "2",
"volume": "147",
"issue": "2",
"pages": "1126-1135"
},
{
"id": "authors:0rvr5-1p492",
"collection": "authors",
"collection_id": "0rvr5-1p492",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20211008-210432594",
"type": "book_section",
"title": "Resolvent-based jet noise models: a projection approach",
"book_title": "AIAA Scitech 2020 Forum",
"author": [
{
"family_name": "Pickering",
"given_name": "Ethan M.",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-Ethan-M"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-Aaron"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-Peter"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Linear resolvent analysis has demonstrated encouraging results for modeling coherent structures in jets when compared against their data-deduced counterparts from high-fidelity large-eddy simulations (LES). However, leveraging resolvent modes for reconstructing statistics of the far acoustic field remains elusive. In this study, we use a LES database to produce an ensemble of realizations for the acoustic field that we project on to a limited set of n resolvent modes. The projections are done on a restricted acoustic output domain, r/D= [5,6], and allow for the LES realizations to be recast in the resolvent basis via a data-deduced, low-rank, n x n cross-spectral density matrix. We find substantial improvements to the acoustic field reconstructions with the addition of a RANS-derived eddy-viscosity model to the resolvent operator. The reconstructions quantitatively match the most energetic regions of the acoustic field across Strouhal numbers, St= [0\u22121], and azimuthal wavenumbers, m= [0,2], using only three resolvent modes. Finally, the characteristics of the resulting n x n covariance matrices are examined and suggest off-diagonal terms may be neglected for n \u2264 3. Results are presented for round, isothermal, Mach 1.5 and 0.9 jets.",
"doi": "10.2514/6.2020-0999",
"isbn": "978-1-62410-595-1",
"publisher": "American Institute of Aeronautics and Astronautics",
"place_of_publication": "Reston, VA",
"publication_date": "2020-01",
"pages": "Art. No. 2020-0999"
},
{
"id": "authors:wnwvz-bmy96",
"collection": "authors",
"collection_id": "wnwvz-bmy96",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190823-093318240",
"type": "article",
"title": "Spatial stability analysis of subsonic corrugated\u00a0jets",
"author": [
{
"family_name": "Laj\u00fas",
"given_name": "F. C., Jr.",
"orcid": "0000-0002-0773-3595",
"clpid": "Laj\u00fas-F-C-Jr"
},
{
"family_name": "Sinha",
"given_name": "A.",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Cavalieri",
"given_name": "A. V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Deschamps",
"given_name": "C. J.",
"orcid": "0000-0001-8912-1295",
"clpid": "Deschamps-C-J"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The linear stability of high-Reynolds-number corrugated jets is investigated by solving the compressible Rayleigh equation linearized about the time-averaged flow field. A Floquet ansatz is used to account for periodicity of this base flow in the azimuthal direction. The origin of multiple unstable solutions, which are known to appear in these non-circular configurations, is traced through gradual perturbations of a parametrized base-flow profile. It is shown that all unstable modes are corrugated jet continuations of the classical Kelvin\u2013Helmholtz modes of circular jets, highlighting that the same instability mechanism, modified by corrugations, leads to the growth of disturbances in such flows. It is found that under certain conditions the eigenvalues may form saddles in the complex plane and display axis switching in their eigenfunctions. A parametric study is also conducted to understand how penetration and number of corrugations impact stability. The effect of these geometric properties on growth rates and phase speeds of the multiple unstable modes is explored, and the results provide guidelines for the development of nozzle configurations that more effectively modify the Kelvin\u2013Helmholtz instability.",
"doi": "10.1017/jfm.2019.573",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2019-10-10",
"volume": "876",
"pages": "766-791"
},
{
"id": "authors:p0k53-7kw05",
"collection": "authors",
"collection_id": "p0k53-7kw05",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20191119-113221067",
"type": "article",
"title": "Furthering resolvent-based jet noise models",
"author": [
{
"family_name": "Pickering",
"given_name": "Ethan M.",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-E-M"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Resolvent analysis continues to provide promising results for modeling the hydrodynamic near-field and acoustic far-field in turbulent jets, particularly when compared to modes deduced through spectral proper orthogonal decomposition (SPOD) of high-fidelity large eddy simulations (LES). Although previous studies have shown that the acoustic field for supersonic jets is of low-rank and primarily described by the Kelvin-Helmholtz instability, the agreement between the acoustically optimal resolvent mode (Kelvin-Helmholtz) and optimal SPOD mode is still lacking. The discrepancy is due to the spatial coloring of turbulent mechanisms in supersonic jets and presents a challenge for reconstructing the acoustic field, as well as the full field flow statistics. To account for coloring, additional (i.e., suboptimal) resolvent modes, associated with the Orr mechanism, must be included and their correlation to other modes determined. Here, we estimate the coloring between resolvent modes by projecting onto an ensemble of LES realizations and reconstructing the realizations in the resolvent basis. The associated projection coefficients provide an ensemble of observations which inherently possess the statistical information necessary to reconstruct the flow and to which we propose a reduced-order stochastic model. We find that the inclusion of a few resolvent suboptimal modes (i.e., Orr-type) allows for modeling of the acoustic field to within 2 dB and increases the region of acoustic agreement when compared to a single mechanism model.",
"doi": "10.1121/1.5137546",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2019-10",
"series_number": "4",
"volume": "146",
"issue": "4",
"pages": "3043"
},
{
"id": "authors:tyze9-akd64",
"collection": "authors",
"collection_id": "tyze9-akd64",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20191119-101701319",
"type": "article",
"title": "Annular and spiral bubble nets: A simulation-focused analysis of humpback whale feeding strategies",
"author": [
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-S-H"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Humpback whales can generate bubbly regions (called bubble nets) via their blowholes, which they appear to exploit via loud vocalizations for feeding purposes. We model this phenomenon as the acoustic excitation of an dilute bubble net of radially varying void fraction. A fully coupled phase-averaging approach is used to compute the bubble response and corresponding acoustics. We first assess the possibility of a sophisticated wave-guidance behavior of high-frequency whale vocalizations within the bubble net. For a small range of flow parameters, the reflections associated with the bubbly region result in an observable wave-guidance behavior, though even then these reflections disperse rapidly. In light of this, we also consider multiple whales surrounding the bubble net, each vocalizing towards its center. We show that for physically realistic configurations, including variations in the bubble net void fraction and number of whales, the bubble net can keep its core region substantially quieter than the exterior. Finally, we investigate the ability of spiral, rather than annular, geometries for keeping the bubble-free region quiet.",
"doi": "10.1121/1.5136599",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2019-10",
"series_number": "4",
"volume": "146",
"issue": "4",
"pages": "2771"
},
{
"id": "authors:zfads-fsn90",
"collection": "authors",
"collection_id": "zfads-fsn90",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190312-090052833",
"type": "article",
"title": "Modeling and simulation of a fluttering cantilever in channel flow",
"author": [
{
"family_name": "Tosi",
"given_name": "Lu\u00eds Phillipe",
"orcid": "0000-0002-0819-4765",
"clpid": "Tosi-L-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Characterizing the dynamics of a cantilever in channel flow is relevant to applications ranging from snoring to energy harvesting. Aeroelastic flutter induces large oscillating amplitudes and sharp changes with frequency that impact the operation of these systems. The fluid\u2013structure mechanisms that drive flutter can vary as the system parameters change, with the stability boundary becoming especially sensitive to the channel height and Reynolds number, especially when either or both are small. In this paper, we develop a coupled fluid\u2013structure model for viscous, two-dimensional channel flow of arbitrary shape. Its flutter boundary is then compared to results of two-dimensional direct numerical simulations to explore the model's validity. Provided the non-dimensional channel height remains small, the analysis shows that the model is not only able to replicate DNS results within the parametric limits that ensure the underlying assumptions are met, but also over a wider range of Reynolds numbers and fluid\u2013structure mass ratios. Model predictions also converge toward an inviscid model for the same geometry as Reynolds number increases.",
"doi": "10.1016/j.jfluidstructs.2019.02.021",
"issn": "0889-9746",
"publisher": "Elsevier",
"publication": "Journal of Fluids and Structures",
"publication_date": "2019-08",
"volume": "89",
"pages": "174-190"
},
{
"id": "authors:d2rc4-0cw13",
"collection": "authors",
"collection_id": "d2rc4-0cw13",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190613-095543057",
"type": "article",
"title": "A critical assessment of the parabolized stability equations",
"author": [
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-Aaron"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-Georgios"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The parabolized stability equations (PSE) are a ubiquitous tool for studying the stability and evolution of disturbances in weakly nonparallel, convectively unstable flows. The PSE method was introduced as an alternative to asymptotic approaches to these problems. More recently, PSE has been applied with mixed results to a more diverse set of problems, often involving flows with multiple relevant instability modes. This paper investigates the limits of validity of PSE via a spectral analysis of the PSE operator. We show that PSE is capable of accurately capturing only disturbances with a single wavelength at each frequency and that other disturbances are not necessarily damped away or properly evolved, as often assumed. This limitation is the result of regularization techniques that are required to suppress instabilities arising from the ill-posedness of treating a boundary value problem as an initial value problem. These findings are valid for both incompressible and compressible formulations of PSE and are particularly relevant for applications involving multiple modes with different wavelengths and growth rates, such as problems involving multiple instability mechanisms, transient growth, and acoustics. Our theoretical results are illustrated using a generic problem from acoustics and a dual-stream jet, and the PSE solutions are compared to both global solutions of the linearized Navier\u2013Stokes equations and a recently developed alternative parabolization.",
"doi": "10.1007/s00162-019-00498-8",
"issn": "0935-4964",
"publisher": "Springer",
"publication": "Theoretical and Computational Fluid Dynamics",
"publication_date": "2019-08",
"series_number": "3-4",
"volume": "33",
"issue": "3-4",
"pages": "359-382"
},
{
"id": "authors:atshr-qb711",
"collection": "authors",
"collection_id": "atshr-qb711",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104729308",
"type": "conference_item",
"title": "Numerical Simulation of Bubbly Cavitating Flow in Shock Wave Lithotripsy",
"author": [
{
"family_name": "Tanguay",
"given_name": "Michel",
"clpid": "Tanguay-M"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The bubbly cavitating flow generated by a lithotriptor is computed using an ensemble averaged two-phase flow model. The time-dependent, compressible flow computation is divided into two separate calculations: the refocusing of a spherical pulse by an ellipsoidal reflector, and the evolution of the steepening wave including the cavitating bubble cloud it generates. The first computation is single phase and is done in prolate spheroidal coordinates in order to have the surface of the ellipsoidal reflector aligned with the computation grid. The output of this simulation is then fed to the two-phase cylindrical coordinates domain. Preliminary results and qualitative comparison to experimental observation are presented.",
"publisher": "Caltech Library",
"publication_date": "2019-07-31"
},
{
"id": "authors:3wzaf-84732",
"collection": "authors",
"collection_id": "3wzaf-84732",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730024",
"type": "conference_item",
"title": "Global Instabilities and Reduced-Order Models of Cavity Flow Oscillations",
"author": [
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Rowley",
"given_name": "C. W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Theofilis",
"given_name": "V.",
"clpid": "Theofilis-V"
}
],
"publisher": "Caltech Library",
"publication_date": "2019-07-31"
},
{
"id": "authors:85yhg-ccv47",
"collection": "authors",
"collection_id": "85yhg-ccv47",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190729-100946483",
"type": "article",
"title": "High-speed video microscopy and numerical modeling of bubble dynamics near a surface of urinary stone",
"author": [
{
"family_name": "Pishchalnikov",
"given_name": "Yuri A.",
"clpid": "Pishchalnikov-Y-A"
},
{
"family_name": "Behnke-Parks",
"given_name": "William M.",
"clpid": "Behnke-Parks-W-M"
},
{
"family_name": "Schmidmayer",
"given_name": "Kevin",
"orcid": "0000-0003-0444-3098",
"clpid": "Schmidmayer-Kevin"
},
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Kenny",
"given_name": "Thomas W.",
"clpid": "Kenny-T-W"
},
{
"family_name": "Laser",
"given_name": "Daniel J.",
"clpid": "Laser-D-J"
}
],
"abstract": "Ultra-high-speed video microscopy and numerical modeling were used to assess the dynamics of microbubbles at the surface of urinary stones. Lipid-shell microbubbles designed to accumulate on stone surfaces were driven by bursts of ultrasound in the sub-MHz range with pressure amplitudes on the order of 1\u2009MPa. Microbubbles were observed to undergo repeated cycles of expansion and violent collapse. At maximum expansion, the microbubbles' cross-section resembled an ellipse truncated by the stone. Approximating the bubble shape as an oblate spheroid, this study modeled the collapse by solving the multicomponent Euler equations with a two-dimensional-axisymmetric code with adaptive mesh refinement for fine resolution of the gas-liquid interface. Modeled bubble collapse and high-speed video microscopy showed a distinctive circumferential pinching during the collapse. In the numerical model, this pinching was associated with bidirectional microjetting normal to the rigid surface and toroidal collapse of the bubble. Modeled pressure spikes had amplitudes two-to-three orders of magnitude greater than that of the driving wave. Micro-computed tomography was used to study surface erosion and formation of microcracks from the action of microbubbles. This study suggests that engineered microbubbles enable stone-treatment modalities with driving pressures significantly lower than those required without the microbubbles.",
"doi": "10.1121/1.5116693",
"pmcid": "PMC6660306",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2019-07",
"series_number": "1",
"volume": "146",
"issue": "1",
"pages": "516-531"
},
{
"id": "authors:wheah-f7357",
"collection": "authors",
"collection_id": "wheah-f7357",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190403-101200730",
"type": "article",
"title": "A quantitative comparison of phase-averaged models for bubbly, cavitating flows",
"author": [
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-S-H"
},
{
"family_name": "Schmidmayer",
"given_name": "Kevin",
"orcid": "0000-0003-0444-3098",
"clpid": "Schmidmayer-Kevin"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We compare the computational performance of two modeling approaches for the flow of dilute cavitation bubbles in a liquid. The first approach is a deterministic model, for which bubbles are represented in a Lagrangian framework as advected features, each sampled from a distribution of equilibrium bubble sizes. The dynamic coupling to the liquid phase is modeled through local volume averaging. The second approach is stochastic; ensemble-phase averaging is used to derive mixture-averaged equations and field equations for the associated bubble properties are evolved in an Eulerian reference frame. For polydisperse mixtures, the probability density function of the equilibrium bubble radii is discretized and bubble properties are solved for each representative bin. In both cases, the equations are closed by solving Rayleigh\u2013Plesset-like equations for the bubble dynamics as forced by the local or mixture-averaged pressure, respectively. An acoustically excited dilute bubble screen is used as a case study for comparisons. We show that observables of ensemble- and volume-averaged simulations match closely and that their convergence is first order under grid refinement. Guidelines are established for phase-averaged simulations by comparing the computational costs of methods. The primary costs are shown to be associated with stochastic closure; polydisperse ensemble-averaging requires many samples of the underlying PDF and volume-averaging requires repeated, randomized simulations to accurately represent a homogeneous bubble population. The relative sensitivities of these costs to spatial resolution and bubble void fraction are presented.",
"doi": "10.1016/j.ijmultiphaseflow.2019.03.028",
"issn": "0301-9322",
"publisher": "Elsevier",
"publication": "International Journal of Multiphase Flow",
"publication_date": "2019-06",
"volume": "115",
"pages": "137-143"
},
{
"id": "authors:xxcqb-b5t73",
"collection": "authors",
"collection_id": "xxcqb-b5t73",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102524",
"type": "conference_item",
"title": "Eddy viscosity for resolvent-based jet noise models",
"author": [
{
"family_name": "Pickering",
"given_name": "Ethan",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-E-M"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-G"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Sipp",
"given_name": "Denis",
"orcid": "0000-0002-2808-3886",
"clpid": "Sipp-D"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
}
],
"abstract": "Response modes computed via linear resolvent analysis have shown promising results for qualitatively modeling both the hydrodynamic and acoustic fields in jets when compared to data-deduced modes from high-fidelity, large-eddy simulations (LES). For an improved quantitative prediction of the near- and far-field, the role of Reynolds stresses must also be considered. In this study, we propose a methodology to deduce an eddy-viscosity model that optimally captures the nonlinear forcing of resolvent modes. The methodology is based on the maximization of the projection between resolvent analysis and spectral proper orthogonal decomposition (SPOD) modes using a Lagrangian optimization framework. For a Mach 0.4 round, isothermal, turbulent jet, four methods are used to increase the projection coefficients: linear damping, spatially constant eddy-viscosity field, a turbulent kinetic energy derived viscosity field, and an optimized eddy-viscosity field. The resulting projection coefficients for the optimized eddy-viscosity field between SPOD and resolvent can be increased to over 90% for frequencies in the range St = 0.35\u22121 with significant improvements to St < 0.35. We find that the use of a frequency-independent turbulent kinetic energy turbulent viscosity model produces modes closely inline with optimal results, providing a preliminary eddy-viscosity resolvent model for jets.",
"doi": "10.2514/6.2019-2454",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2019-05-18"
},
{
"id": "authors:yj39b-ecz26",
"collection": "authors",
"collection_id": "yj39b-ecz26",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102671",
"type": "conference_item",
"title": "Resolvent-based analysis of streaks in turbulent jets",
"author": [
{
"family_name": "Nogueira",
"given_name": "Petr\u00f4nio A. S.",
"clpid": "Nogueira-P-A"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Jaunet",
"given_name": "Vincent",
"clpid": "Jaunet-V"
},
{
"family_name": "Pickering",
"given_name": "Ethan",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-E-M"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-G"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Large scale, elongated structures, similar those ones widely studied in wall-bounded flows, are also present in turbulent jets. Several characteristics of these streaks can be identified via reduced order models such as resolvent analysis. The present work involves a resolvent-based study of these structures in turbulent jets. We focus on obtaining the optimal forcing that generates these energetic coherent structures. Results are compared with experimental data post-processed using spectral proper orthogonal decomposition, allowing us to draw conclusions about the nature of the non-linear forcing, since the two analyses should provide equivalent results if this term is modelled as spatially white. By identifying streaks in a global framework, we expect to better understand the mechanism by which they are generated.",
"doi": "10.2514/6.2019-2569",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2019-05-18"
},
{
"id": "authors:88z72-ng038",
"collection": "authors",
"collection_id": "88z72-ng038",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102068",
"type": "conference_item",
"title": "Streaks and coherent structures in jets from round and serrated nozzles",
"author": [
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-G"
},
{
"family_name": "Pickering",
"given_name": "Ethan",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-E-M"
},
{
"family_name": "Schmidt",
"given_name": "Oliver",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Nogueira",
"given_name": "Petr\u00f4nio A. S.",
"clpid": "Nogueira-P-A"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Hydrodynamic instabilities are directly related to large-scale coherent structures that are correlated with jet noise emission. Unravelling and accurately predicting their fundamental dynamics shows a promising direction for designing quieter jet engines. In this study, we analyze high-fidelity large-eddy simulation data of a turbulent Mach 0.4 round jet and a Mach 1.5 chevron jet. Using spectral proper orthogonal decomposition we identify, beyond the well-known Kelvin\u2013Helmoholtz and Orr mechanisms, elongated alternating streamwise streaks of high and low-speed fluid that have been associated with a non-modal lift-up effect in wall-bounded shear flows. In the global three-dimensional domain, the most energetic streaks manifest for azimuthal wavenumber m = 1 and frequency St \u2192 0. Furthermore, for the chevron jet, streaks and streamwise vortices appear due to the presence of the serrated nozzle, and they inherit the periodicity of the nozzle geometry. Finally, local (planar) spectral proper orthogonal decomposition is used to analyze the coherent structures of the chevron jet flow. Near the nozzle exit, antisymmetric and symmetric modes appear to be amplified and linked to the presence of the chevrons/streaks. Further downstream, the most energetic modes share similar characteristics to the ones observed in round jets.",
"doi": "10.2514/6.2019-2597",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2019-05-18"
},
{
"id": "authors:hf1ft-76c23",
"collection": "authors",
"collection_id": "hf1ft-76c23",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059850",
"type": "conference_item",
"title": "A comparison of ensemble- and volume-averaged bubbly flow models",
"author": [
{
"family_name": "Bryngelson",
"given_name": "Spencer H.",
"orcid": "0000-0003-1750-7265",
"clpid": "Bryngelson-S-H"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We compare volume- and ensemble-averaged bubbly flow models. Volume-averaging is a deterministic process for which bubbles are represented in a Lagrangian framework as advected particles, each sampled from a distribution of equilibrium bubble sizes. Ensemble-averaging instead uses mixture-averaged equations in an Eulerian reference frame for the associated bubble properties, each represented by bins of the equilibrium distribution. In both cases, bubbles are modeled as spherical with dynamics governed by the Keller-Miksis equation. Computationally, there are tradeoffs between these two approaches. Here, we simulate an acoustically excited dilute bubble screen and compare the computational efficiency of the two approaches.",
"publisher": "Caltech Library",
"publication_date": "2019-05"
},
{
"id": "authors:98rv2-x9015",
"collection": "authors",
"collection_id": "98rv2-x9015",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100886",
"type": "conference_item",
"title": "A comparative study on interface-capturing models and schemes to solve bubble dynamics and cavitation",
"author": [
{
"family_name": "Schmidmayer",
"given_name": "Kevin",
"orcid": "0000-0003-0444-3098",
"clpid": "Schmidmayer-Kevin"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "In the context of simulation of bubble dynamics and cavitation, even the simple problem of the collapse of a spherical bubble is challenging to compute accurately with general, three-dimensional, interface-capturing schemes. Difficulties arise from both the physical model of the multicomponent fluid and the discretization scheme. Pathologies associated with each factor are identified and solutions to remedy specific issues are proposed.",
"publisher": "Caltech Library",
"publication_date": "2019-05"
},
{
"id": "authors:jhb95-fxs05",
"collection": "authors",
"collection_id": "jhb95-fxs05",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190410-092338329",
"type": "article",
"title": "Comparative study of the dynamics of laser and acoustically generated bubbles in viscoelastic media",
"author": [
{
"family_name": "Wilson",
"given_name": "Chad T.",
"clpid": "Wilson-C-T"
},
{
"family_name": "Hall",
"given_name": "Timothy L.",
"clpid": "Hall-T-L"
},
{
"family_name": "Johnsen",
"given_name": "Eric",
"clpid": "Johnsen-E"
},
{
"family_name": "Mancia",
"given_name": "Lauren",
"orcid": "0000-0003-4366-1944",
"clpid": "Mancia-L"
},
{
"family_name": "Rodriguez",
"given_name": "Mauro",
"clpid": "Rodriguez-M"
},
{
"family_name": "Lundt",
"given_name": "Jonathan E.",
"clpid": "Lundt-J-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Henann",
"given_name": "David L.",
"clpid": "Henann-D-L"
},
{
"family_name": "Franck",
"given_name": "Christian",
"clpid": "Franck-C"
},
{
"family_name": "Xu",
"given_name": "Zhen",
"clpid": "Xu-Zhen"
},
{
"family_name": "Sukovich",
"given_name": "Jonathan R.",
"clpid": "Sukovich-J-R"
}
],
"abstract": "Experimental observations of the growth and collapse of acoustically and laser-nucleated single bubbles in water and agarose gels of varying stiffness are presented. The maximum radii of generated bubbles decreased as the stiffness of the media increased for both nucleation modalities, but the maximum radii of laser-nucleated bubbles decreased more rapidly than acoustically nucleated bubbles as the gel stiffness increased. For water and low stiffness gels, the collapse times were well predicted by a Rayleigh cavity, but bubbles collapsed faster than predicted in the higher stiffness gels. The growth and collapse phases occurred symmetrically (in time) about the maximum radius in water but not in gels, where the duration of the growth phase decreased more than the collapse phase as gel stiffness increased. Numerical simulations of the bubble dynamics in viscoelastic media showed varying degrees of success in accurately predicting the observations.",
"doi": "10.1103/physreve.99.043103",
"issn": "2470-0045",
"publisher": "American Physical Society",
"publication": "Physical Review E",
"publication_date": "2019-04",
"series_number": "4",
"volume": "99",
"issue": "4",
"pages": "Art. No. 043103"
},
{
"id": "authors:dwj3s-xp206",
"collection": "authors",
"collection_id": "dwj3s-xp206",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180828-125637273",
"type": "article",
"title": "Bubble cloud dynamics in an ultrasound field",
"author": [
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The dynamics of bubble clouds induced by high-intensity focused ultrasound is investigated in a regime where the cloud size is similar to the ultrasound wavelength. High-speed images show that the cloud is asymmetric; the bubbles nearest the source grow to a larger radius than the distal ones. Similar structures of bubble clouds are observed in numerical simulations that mimic the laboratory experiment. To elucidate the structure, a parametric study is conducted for plane ultrasound waves with various amplitudes and diffuse clouds with different initial void fractions. Based on an analysis of the kinetic energy of liquid induced by bubble oscillations, a new scaling parameter is introduced to characterize the dynamics. The new parameter generalizes the cloud interaction parameter originally introduced by d'Agostino & Brennen (J. Fluid Mech., vol. 199, 1989, pp. 155\u2013176). The dynamic interaction parameter controls the energy localization and consequent anisotropy of the cloud. Moreover, the amplitude of the far-field, bubble-scattered acoustics is likewise correlated with the proposed parameter. Findings of the present study not only shed light on the physics of cloud cavitation, but may also be of use for the quantification of the effects of cavitation on outcomes of ultrasound therapies including high-intensity focused ultrasound-based lithotripsy.",
"doi": "10.1017/jfm.2018.968",
"pmcid": "PMC6761994",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2019-03-10",
"volume": "862",
"pages": "1105-1134"
},
{
"id": "authors:qsf67-tpx91",
"collection": "authors",
"collection_id": "qsf67-tpx91",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180122-091425148",
"type": "article",
"title": "Global modes and nonlinear analysis of inverted-flag flapping",
"author": [
{
"family_name": "Goza",
"given_name": "Andres",
"orcid": "0000-0002-9372-7713",
"clpid": "Goza-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Sader",
"given_name": "John E.",
"orcid": "0000-0002-7096-0627",
"clpid": "Sader-J-E"
}
],
"abstract": "An inverted flag has its trailing edge clamped and exhibits dynamics distinct from that of a conventional flag, whose leading edge is restrained. We perform nonlinear simulations and a global stability analysis of the inverted-flag system for a range of Reynolds numbers, flag masses and stiffnesses. Our global stability analysis is based on a linearisation of the fully coupled fluid\u2013structure system of equations. The calculated equilibria are steady-state solutions of the fully coupled nonlinear equations. By implementing this approach, we (i) explore the mechanisms that initiate flapping, (ii) study the role of vorticity generation and vortex-induced vibration (VIV) in large-amplitude flapping and (iii) characterise the chaotic flapping regime. For point (i), we identify a deformed-equilibrium state and show through a global stability analysis that the onset of small-deflection flapping \u2013 where the oscillation amplitude is significantly smaller than in large-amplitude flapping \u2013 is due to a supercritical Hopf bifurcation. For large-amplitude flapping, point (ii), we confirm the arguments of Sader et al. (J. Fluid Mech., vol. 793, 2016a) that classical VIV exists when the flag is sufficiently light with respect to the fluid. We also show that for heavier flags, large-amplitude flapping persists (even for Reynolds numbers < 50) and is not classical VIV. Finally, with respect to point (iii), chaotic flapping has been observed experimentally for Reynolds numbers of O(10^4) , and here we show that chaos also persists at a moderate Reynolds number of 200. We characterise this chaotic regime and calculate its strange attractor, whose structure is controlled by the above-mentioned deformed equilibria and is similar to a Lorenz attractor.",
"doi": "10.1017/jfm.2018.728",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2018-12-25",
"volume": "857",
"pages": "312-344"
},
{
"id": "authors:nq2j6-93t97",
"collection": "authors",
"collection_id": "nq2j6-93t97",
"cite_using_url": "https://authors.library.caltech.edu/records/nq2j6-93t97",
"type": "article",
"title": "Global modes and nonlinear analysis of inverted-flag flapping",
"author": [
{
"family_name": "Goza",
"given_name": "Andres",
"orcid": "0000-0002-9372-7713",
"clpid": "Goza-Andres"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Sader",
"given_name": "John E.",
"orcid": "0000-0002-7096-0627",
"clpid": "Sader-J-E"
}
],
"abstract": "An inverted flag has its trailing edge clamped and exhibits dynamics distinct from that of a conventional flag, whose leading edge is restrained. We perform nonlinear simulations and a global stability analysis of the inverted-flag system for a range of Reynolds numbers, flag masses and stiffnesses. Our global stability analysis is based on a linearisation of the fully coupled fluid\u2013structure system of equations. The calculated equilibria are steady-state solutions of the fully coupled nonlinear equations. By implementing this approach, we (i) explore the mechanisms that initiate flapping, (ii) study the role of vorticity generation and vortex-induced vibration (VIV) in large-amplitude flapping and (iii) characterise the chaotic flapping regime. For point (i), we identify a deformed-equilibrium state and show through a global stability analysis that the onset of small-deflection flapping \u2013 where the oscillation amplitude is significantly smaller than in large-amplitude flapping \u2013 is due to a supercritical Hopf bifurcation. For large-amplitude flapping, point (ii), we confirm the arguments of Sader et al. (J. Fluid Mech., vol. 793, 2016a) that classical VIV exists when the flag is sufficiently light with respect to the fluid. We also show that for heavier flags, large-amplitude flapping persists (even for Reynolds numbers <50 ) and is not classical VIV. Finally, with respect to point (iii), chaotic flapping has been observed experimentally for Reynolds numbers of O(10\u2074) , and here we show that chaos also persists at a moderate Reynolds number of 200. We characterise this chaotic regime and calculate its strange attractor, whose structure is controlled by the above-mentioned deformed equilibria and is similar to a Lorenz attractor.
",
"doi": "10.1017/jfm.2018.728",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2018-12-25",
"volume": "857",
"pages": "312-344"
},
{
"id": "authors:txhh8-1d492",
"collection": "authors",
"collection_id": "txhh8-1d492",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181213-103728580",
"type": "article",
"title": "Data-assimilated low-order vortex modeling of separated flows",
"author": [
{
"family_name": "Darakananda",
"given_name": "Darwin",
"clpid": "Darakananda-D"
},
{
"family_name": "de Castro da Silva",
"given_name": "Andr\u00e9 Fernando",
"clpid": "de-Castro-da-Silva-A-F"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Eldredge",
"given_name": "Jeff D.",
"clpid": "Eldredge-J-D"
}
],
"abstract": "Vortex models have been used for decades as computationally efficient tools to investigate unsteady aerodynamics. However, their utility for separated flows\u2014particularly when such flows are subjected to incident disturbances\u2014has been hindered by the tradeoff between the model's physical fidelity and its expectation for fast prediction (e.g., relative to computational fluid dynamics). In this work, it is shown that physical fidelity and speed can be simultaneously achieved by assimilating measurement data into the model to compensate for unrepresented physics. The underlying inviscid vortex model captures the transport of vortex structures with a standard collection of regularized vortex elements that interact mutually and with an infinitely thin flat plate. In order to maintain a low-dimensional representation, with fewer than O(100) degrees of freedom, an aggregation procedure is developed and utilized in which vortex elements are coalesced at each time step. A flow state vector, composed of vortex element properties as well as the critical leading-edge suction parameter, is advanced within an ensemble Kalman filter (EnKF) framework. In this framework, surface pressure is used to correct the states of an ensemble of randomly initiated vortex models. The overall algorithm is applied to several scenarios of an impulsively started flat plate, in which data from a high-fidelity Navier-Stokes simulation at Reynolds number 500 are used as a surrogate for the measurements. The assimilated vortex model efficiently and accurately predicts the evolving flow as well as the normal force in both the undisturbed case (a separated flow) as well as in the presence of one or more incident gusts, despite lack of a priori knowledge of the gust's characteristics.",
"doi": "10.1103/physrevfluids.3.124701",
"issn": "2469-990X",
"publisher": "American Physical Society",
"publication": "Physical Review Fluids",
"publication_date": "2018-12",
"series_number": "12",
"volume": "3",
"issue": "12",
"pages": "Art. No. 124701"
},
{
"id": "authors:8af3f-64f78",
"collection": "authors",
"collection_id": "8af3f-64f78",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180618-080041218",
"type": "article",
"title": "Spectral analysis of jet turbulence",
"author": [
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-G"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "Informed by large-eddy simulation (LES) data and resolvent analysis of the mean flow, we examine the structure of turbulence in jets in the subsonic, transonic and supersonic regimes. Spectral (frequency-space) proper orthogonal decomposition is used to extract energy spectra and decompose the flow into energy-ranked coherent structures. The educed structures are generally well predicted by the resolvent analysis. Over a range of low frequencies and the first few azimuthal mode numbers, these jets exhibit a low-rank response characterized by Kelvin\u2013Helmholtz (KH) type wavepackets associated with the annular shear layer up to the end of the potential core and that are excited by forcing in the very-near-nozzle shear layer. These modes too have been experimentally observed before and predicted by quasi-parallel stability theory and other approximations \u2013 they comprise a considerable portion of the total turbulent energy. At still lower frequencies, particularly for the axisymmetric mode, and again at high frequencies for all azimuthal wavenumbers, the response is not low-rank, but consists of a family of similarly amplified modes. These modes, which are primarily active downstream of the potential core, are associated with the Orr mechanism. They occur also as subdominant modes in the range of frequencies dominated by the KH response. Our global analysis helps tie together previous observations based on local spatial stability theory, and explains why quasi-parallel predictions were successful at some frequencies and azimuthal wavenumbers, but failed at others.",
"doi": "10.1017/jfm.2018.675",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2018-11-25",
"volume": "855",
"pages": "953-982"
},
{
"id": "authors:yv875-3s862",
"collection": "authors",
"collection_id": "yv875-3s862",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190123-101938742",
"type": "article",
"title": "Experimental observations and numerical modeling of lipid-shell microbubbles with calcium-adhering moieties for minimally-invasive treatment of urinary stones",
"author": [
{
"family_name": "Pishchalnikov",
"given_name": "Yuri A.",
"clpid": "Pishchalnikov-Y-A"
},
{
"family_name": "Behnke-Parks",
"given_name": "William",
"clpid": "Behnke-Parks-W"
},
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Mellema",
"given_name": "Matthew",
"clpid": "Mellema-M"
},
{
"family_name": "Hopcroft",
"given_name": "Matthew",
"clpid": "Hopcroft-M"
},
{
"family_name": "Luong",
"given_name": "Alice",
"clpid": "Luong-Alice"
},
{
"family_name": "Wiener",
"given_name": "Scott",
"clpid": "Wiener-S"
},
{
"family_name": "Stoller",
"given_name": "Marshall L.",
"clpid": "Stoller-M-L"
},
{
"family_name": "Kenny",
"given_name": "Thomas",
"clpid": "Kenny-T"
},
{
"family_name": "Laser",
"given_name": "Daniel J.",
"clpid": "Laser-D-J"
}
],
"abstract": "A novel treatment modality incorporating calcium-adhering microbubbles has recently entered human clinical trials as a new minimally-invasive approach to treat urinary stones. In this treatment method, lipid-shell gas-core microbubbles can be introduced into the urinary tract through a catheter. Lipid moities with calcium-adherance properties incorporated into the lipid shell facilitate binding to stones. The microbubbles can be excited by an extracorporeal source of quasi-collimated ultrasound. Alternatively, the microbubbles can be excited by an intraluminal source, such as a fiber-optic laser. With either excitation technique, calcium-adhering microbubbles can significantly increase rates of erosion, pitting, and fragmentation of stones. We report here on new experiments using high-speed photography to characterize microbubble expansion and collapse. The bubble geometry observed in the experiments was used as one of the initial shapes for the numerical modeling. The modeling showed that the bubble dynamics strongly depends on bubble shape and stand-off distance. For the experimentally observed shape of microbubbles, the numerical modeling showed that the collapse of the microbubbles was associated with pressure increases of some two-to-three orders of magnitude compared to the excitation source pressures. This in-vitro study provides key insights into the use of microbubbles with calcium-adhering moieties in treatment of urinary stones.",
"doi": "10.1121/2.0000958",
"pmcid": "PMC7241592",
"issn": "1939-800X",
"publisher": "Acoustical Society of America",
"publication": "Proceedings of Meetings on Acoustics",
"publication_date": "2018-11-05",
"series_number": "1",
"volume": "35",
"issue": "1",
"pages": "Art. No. 020008"
},
{
"id": "authors:3xr1b-1ar53",
"collection": "authors",
"collection_id": "3xr1b-1ar53",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190123-080437707",
"type": "article",
"title": "Modeling and numerical simulation of the bubble cloud dynamics in an ultrasound field for burst wave lithotripsy",
"author": [
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Maxwell",
"given_name": "Adam",
"clpid": "Maxwell-A-D"
},
{
"family_name": "Kreider",
"given_name": "Wayne",
"clpid": "Kreider-W"
},
{
"family_name": "Bailey",
"given_name": "Michael",
"clpid": "Bailey-M-R"
}
],
"abstract": "Modeling and numerical simulation of bubble clouds induced by intense ultrasound waves are conducted to quantify the effect of cloud cavitation on burst wave lithotripsy, a proposed non-invasive alternative to shock wave lithotripsy that uses pulses of ultrasound with an amplitude of O(1) MPa and a frequency of O(100) kHz. A unidirectional acoustic source model and an Eulerian-Lagrangian method are developed for simulation of ultrasound generation from a multi-element array transducer and cavitation bubbles, respectively. Parametric simulations of the spherical bubble cloud dynamics reveal a new scaling parameter that dictates both the structure of the bubble cloud and the amplitude of the far-field, bubble-scattered acoustics. The simulation further shows that a thin layer of bubble clouds nucleated near a kidney stone model can shield up to 90% of the incoming wave energy, indicating a potential loss of efficacy during the treatment due to cavitation. Strong correlations are identified between the far-field, bubble-scattered acoustics and the magnitude of the shielding, which could be used for ultrasound monitoring of cavitation during treatments. The simulations are validated by companion experiments in vitro.",
"doi": "10.1121/2.0000946",
"issn": "1939-800X",
"publisher": "Acoustical Society of America",
"publication": "Proceedings of Meetings on Acoustics",
"publication_date": "2018-11-05",
"series_number": "1",
"volume": "35",
"issue": "1",
"pages": "Art. No. 020006"
},
{
"id": "authors:ywdh7-6f031",
"collection": "authors",
"collection_id": "ywdh7-6f031",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180827-090424631",
"type": "article",
"title": "Energy shielding by cavitation bubble clouds in burst wave lithotripsy",
"author": [
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Maxwell",
"given_name": "Adam D.",
"clpid": "Maxwell-Adam-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Kreider",
"given_name": "Wayne",
"clpid": "Kreider-Wayne"
},
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-Michael-R"
}
],
"abstract": "Combined laboratory experiment and numerical simulation are conducted on bubble clouds nucleated on the surface of a model kidney stone to quantify the energy shielding of the stone caused by cavitation during burst wave lithotripsy (BWL). In the experiment, the bubble clouds are visualized and bubble-scattered acoustics are measured. In the simulation, a compressible, multi-component flow solver is used to capture complex interactions among cavitation bubbles, the stone, and the burst wave. Quantitative agreement is confirmed between results of the experiment and the simulation. In the simulation, a significant shielding of incident wave energy by the bubble clouds is quantified. The magnitude of shielding can reach up to 90% of the energy of the incoming burst wave that otherwise would be transmitted into the stone, suggesting a potential loss of efficacy of stone comminution. There is a strong correlation between the magnitude of the energy shielding and the amplitude of the bubble-scattered acoustics, independent of the initial size and the void fraction of the bubble cloud within a range addressed in the simulation. This correlation could provide for real-time monitoring of cavitation activity in BWL.",
"doi": "10.1121/1.5079641",
"pmcid": "PMC6258362",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2018-11",
"series_number": "5",
"volume": "144",
"issue": "5",
"pages": "2952-2961"
},
{
"id": "authors:sfm72-ba678",
"collection": "authors",
"collection_id": "sfm72-ba678",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180828-133412782",
"type": "article",
"title": "Jet-edge interaction tones",
"author": [
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Jaunet",
"given_name": "Vincent",
"clpid": "Jaunet-V"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Schmidt",
"given_name": "Oliver",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Agarwal",
"given_name": "Anurag",
"clpid": "Agarwal-A"
}
],
"abstract": "Motivated by the problem of jet\u2013flap interaction noise, we study the tonal dynamics that occurs when an isothermal turbulent jet grazes a sharp edge. We perform hydrodynamic and acoustic pressure measurements to characterise the tones as a function of Mach number and streamwise edge position. The observed distribution of spectral peaks cannot be explained using the usual edge-tone model, in which resonance is underpinned by coupling between downstream-travelling Kelvin\u2013Helmholtz wavepackets and upstream-travelling sound waves. We show, rather, that the strongest tones are due to coupling between Kelvin\u2013Helmholtz wavepackets and a family of trapped, upstream-travelling acoustic modes in the potential core, recently studied by Towne et al. (J. Fluid Mech. vol. 825, 2017) and Schmidt et al. (J. Fluid Mech. vol. 825, 2017). We also study the band-limited nature of the resonance, showing the high-frequency cutoff to be due to the frequency dependence of the upstream-travelling waves. Specifically, at high Mach number, these modes become evanescent above a certain frequency, whereas at low Mach number they become progressively trapped with increasing frequency, which inhibits their reflection in the nozzle plane.",
"doi": "10.1017/jfm.2018.566",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2018-10-25",
"volume": "853",
"pages": "333-358"
},
{
"id": "authors:rc87r-jvn05",
"collection": "authors",
"collection_id": "rc87r-jvn05",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102441",
"type": "article",
"title": "Experimental observations and numerical modeling of lipid-shell microbubbles with stone targeting moieties for minimally-invasive treatment of urinary stones",
"author": [
{
"family_name": "Pishchalnikov",
"given_name": "Yuri A.",
"clpid": "Pishchalnikov-Y-A"
},
{
"family_name": "Behnke-Parks",
"given_name": "William",
"clpid": "Behnke-Parks-W"
},
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Mellema",
"given_name": "Matt",
"clpid": "Mellema-M"
},
{
"family_name": "Hopcroft",
"given_name": "Matt",
"clpid": "Hopcroft-M"
},
{
"family_name": "Luong",
"given_name": "Alice",
"clpid": "Luong-Alice"
},
{
"family_name": "Wiener",
"given_name": "Scott",
"clpid": "Wiener-S"
},
{
"family_name": "Stoller",
"given_name": "Marshall",
"clpid": "Stoller-M-L"
},
{
"family_name": "Kenny",
"given_name": "Thomas",
"clpid": "Kenny-T"
},
{
"family_name": "Laser",
"given_name": "Daniel",
"clpid": "Laser-D"
}
],
"abstract": "Products incorporating stone-targeting microbubbles have recently entered human clinical trials as a new minimally-invasive approach to treat urinary stones. Lipid-shell, gas-core microbubbles can be introduced into the urinary tract through a catheter. Calcium-binding moieties incorporated into the lipid shell can facilitate binding to stones. The microbubbles can be excited by an extracorporeal source of low-intensity ultrasound. Alternatively, the microbubbles can be excited by an intraluminal source, such as a fiber-optic laser. With either excitation technique, stone-targeting microbubbles can significantly increase rates of erosion, pitting, and fragmentation of stones, as has recently been reported for in-vitro experiments with synthetic stones [Wiener et al., J. Urology, v.199, no.4S, e322 (2018)]. We report here on new experiments using high-speed photography to characterize microbubbles expansion of cracks within a stone and resultant breaking-off of stone fragments. Numerical modeling shows that the direction of microjets produced by collapsing stone-bound microbubbles depends strongly on bubble shape and stand-off distance. For a wide range of stand-off distances and bubble shapes, microbubble collapse is associated with pressure increases of some two orders of magnitude compared to the excitation source pressures. This in-vitro study provides key insights into the use of stone-targeting microbubbles in treatment of urinary stones.",
"doi": "10.1121/1.5067871",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2018-10-19",
"series_number": "3",
"volume": "144",
"issue": "3",
"pages": "1781"
},
{
"id": "authors:ypvz9-xqg97",
"collection": "authors",
"collection_id": "ypvz9-xqg97",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180518-133233019",
"type": "article",
"title": "Eulerian-Lagrangian method for simulation of cloud cavitation",
"author": [
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We present a coupled Eulerian\u2013Lagrangian method to simulate cloud cavitation in a compressible liquid. The method is designed to capture the strong, volumetric oscillations of each bubble and the bubble-scattered acoustics. The dynamics of the bubbly mixture is formulated using volume-averaged equations of motion. The continuous phase is discretized on an Eulerian grid and integrated using a high-order, finite-volume weighted essentially non-oscillatory (WENO) scheme, while the gas phase is modeled as spherical, Lagrangian point-bubbles at the sub-grid scale, each of whose radial evolution is tracked by solving the Keller\u2013Miksis equation. The volume of bubbles is mapped onto the Eulerian grid as the void fraction by using a regularization (smearing) kernel. In the most general case, where the bubble distribution is arbitrary, three-dimensional Cartesian grids are used for spatial discretization. In order to reduce the computational cost for problems possessing translational or rotational homogeneities, we spatially average the governing equations along the direction of symmetry and discretize the continuous phase on two-dimensional or axi-symmetric grids, respectively. We specify a regularization kernel that maps the three-dimensional distribution of bubbles onto the field of an averaged two-dimensional or axi-symmetric void fraction. A closure is developed to model the pressure fluctuations at the sub-grid scale as synthetic noise. For the examples considered here, modeling the sub-grid pressure fluctuations as white noise agrees a priori with computed distributions from three-dimensional simulations, and suffices, a posteriori, to accurately reproduce the statistics of the bubble dynamics. The numerical method and its verification are described by considering test cases of the dynamics of a single bubble and cloud cavitation induced by ultrasound fields.",
"doi": "10.1016/j.jcp.2018.05.029",
"pmcid": "PMC6364854",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2018-10-15",
"volume": "371",
"pages": "994-1017"
},
{
"id": "authors:r63dp-njj61",
"collection": "authors",
"collection_id": "r63dp-njj61",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180801-142726732",
"type": "article",
"title": "Importance of the nozzle-exit boundary-layer state in subsonic turbulent jets",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Jaunet",
"given_name": "Vincent",
"clpid": "Jaunet-V"
},
{
"family_name": "Le Rallic",
"given_name": "Maxime",
"clpid": "Le-Rallic-M"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
}
],
"abstract": "To investigate the effects of the nozzle-exit conditions on jet flow and sound fields, large-eddy simulations of an isothermal Mach 0.9 jet issued from a convergent-straight nozzle are performed at a diameter-based Reynolds number of 1 x 10^6. The simulations feature near-wall adaptive mesh refinement, synthetic turbulence and wall modelling inside the nozzle. This leads to fully turbulent nozzle-exit boundary layers and results in significant improvements for the flow field and sound predictions compared with those obtained from the typical approach based on laminar flow in the nozzle. The far-field pressure spectra for the turbulent jet match companion experimental measurements, which use a boundary-layer trip to ensure a turbulent nozzle-exit boundary layer to within 0.5 dB for all relevant angles and frequencies. By contrast, the initially laminar jet results in greater high-frequency noise. For both initially laminar and turbulent jets, decomposition of the radiated noise into azimuthal Fourier modes is performed, and the results show similar azimuthal characteristics for the two jets. The axisymmetric mode is the dominant source of sound at the peak radiation angles and frequencies. The first three azimuthal modes recover more than 97 % of the total acoustic energy at these angles and more than 65 % (i.e. error less than 2 dB) for all angles. For the main azimuthal modes, linear stability analysis of the near-nozzle mean-velocity profiles is conducted in both jets. The analysis suggests that the differences in radiated noise between the initially laminar and turbulent jets are related to the differences in growth rate of the Kelvin\u2013Helmholtz mode in the near-nozzle region.",
"doi": "10.1017/jfm.2018.476",
"issn": "0022-1120",
"publisher": "Journal of Fluid Mechanics",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2018-09-25",
"volume": "851",
"pages": "83-124"
},
{
"id": "authors:ynke9-q5h47",
"collection": "authors",
"collection_id": "ynke9-q5h47",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181107-131334414",
"type": "article",
"title": "Spectral analysis of jet turbulence and radiated sound",
"author": [
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-G"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "Informed by LES data and resolvent analysis of the mean flow, we examine the structure of turbulence in jets in the subsonic, transonic, and supersonic regimes. Spectral (frequency-space) proper orthogonal decomposition is used to extract energy spectra and decompose the flow into energy-ranked coherent structures. We demonstrate that two distinct mechanisms, which can be distinguished by their characteristic frequency scaling and spatial support, lead to the formation of wavepackets\u2014coherent structures that are known for their acoustic importance in the aft-angle radiation of high subsonic and supersonic jets. We compare these characteristics to acoustic source features extracted from hologram sound pressure measurements in a recent publication. The evidence strongly suggests that both mechanisms are active in full-scale jets and comprise the experimentally educed sources of sound.",
"doi": "10.1121/1.5067451",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2018-09",
"series_number": "3",
"volume": "144",
"issue": "3",
"pages": "Art. No. 1673"
},
{
"id": "authors:z4n4s-qge26",
"collection": "authors",
"collection_id": "z4n4s-qge26",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181022-152225740",
"type": "article",
"title": "Modeling and numerical simulation of the bubble cloud dynamics in an ultrasound field for burst wave lithotripsy",
"author": [
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Maxwell",
"given_name": "Adam D.",
"clpid": "Maxwell-A-D"
},
{
"family_name": "Kreider",
"given_name": "Wayne",
"clpid": "Kreider-W"
},
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-M-R"
}
],
"abstract": "Modeling and numerical simulation of bubble clouds induced by intense ultrasound waves are conducted to quantify the effect of cloud cavitation on burst wave lithotripsy, a proposed non-invasive alternative to shock wave lithotripsy that uses pulses of ultrasound with an amplitude of O(1) MPa and a frequency of O(100) kHz. A unidirectional acoustic source model and an Eulerian-Lagrangian method are developed for simulation of ultrasound generation from a multi-element array transducer and cavitation bubbles, respectively. Parametric simulations of the spherical bubble cloud dynamics reveal a new scaling parameter that dictates both the structure of the bubble cloud and the amplitude of the far-field, bubble-scattered acoustics. The simulation further shows that a thin layer of bubble clouds nucleated near a kidney stone model can shield up to 90% of the incoming wave energy, indicating a potential loss of efficacy during the treatment due to cavitation. Strong correlations are identified between the far-field, bubble-scattered acoustics and the magnitude of the shielding, which could be used for ultrasound monitoring of cavitation during treatments. The simulations are validated by companion experiments in vitro.",
"doi": "10.1121/1.5067866",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2018-09",
"series_number": "3",
"volume": "144",
"issue": "3",
"pages": "Art. No. 1780"
},
{
"id": "authors:mwxkf-7ac87",
"collection": "authors",
"collection_id": "mwxkf-7ac87",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20181102-084214143",
"type": "article",
"title": "Resolvent analysis for jet noise source identification",
"author": [
{
"family_name": "Pickering",
"given_name": "Ethan M.",
"orcid": "0000-0002-4485-6359",
"clpid": "Pickering-E-M"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-G"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We use resolvent analysis and spectral proper orthogonal decomposition (SPOD) to deduce the acoustic sources for an isothermal Mach 1.5 round jet. Both physics-based resolvent analysis and data-driven SPOD (using a high-fidelity, experimentally-verified, large-eddy simulation (LES) database) provide a basis for predicting the perturbation field. Singular value decomposition of the resolvent operator based upon the LES baseflow provides optimal volumetric forcing modes, or sources, and their associated linear responses. To identify physically relevant resolvent modes, comparisons are made between the highest gain responses and the highest energy SPOD modes computed directly from LES realizations. The prevalence of the associated resolvent forcing modes in the data are then assessed by projecting them onto the full LES nonlinear terms. The resulting distributions are presented and a jet noise model leveraging these forcing statistics is discussed.",
"doi": "10.1121/1.5067573",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2018-09",
"series_number": "3",
"volume": "144",
"issue": "3",
"pages": "Art. No. 1706"
},
{
"id": "authors:erqg4-57g18",
"collection": "authors",
"collection_id": "erqg4-57g18",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180529-085928867",
"type": "article",
"title": "Modal decomposition of fluid-structure interaction with application to flag flapping",
"author": [
{
"family_name": "Goza",
"given_name": "Andres",
"orcid": "0000-0002-9372-7713",
"clpid": "Goza-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Modal decompositions such as proper orthogonal decomposition (POD), dynamic mode decomposition (DMD) and their variants are regularly used to educe physical mechanisms of nonlinear flow phenomena that cannot be easily understood through direct inspection. In fluid\u2013structure interaction (FSI) systems, fluid motion is coupled to vibration and/or deformation of an immersed structure. Despite this coupling, data analysis is often performed using only fluid or structure variables, rather than incorporating both. This approach does not provide information about the manner in which fluid and structure modes are correlated. We present a framework for performing POD and DMD where the fluid and structure are treated together. As part of this framework, we introduce a physically meaningful norm for FSI systems. We first use this combined fluid\u2013structure formulation to identify correlated flow features and structural motions in limit-cycle flag flapping. We then investigate the transition from limit-cycle flapping to chaotic flapping, which can be initiated by increasing the flag mass. Our modal decomposition reveals that at the onset of chaos, the dominant flapping motion increases in amplitude and leads to a bluff-body wake instability. This new bluff-body mode interacts triadically with the dominant flapping motion to produce flapping at the non-integer harmonic frequencies previously reported by Connell and Yue (2007). While our formulation is presented for POD and DMD, there are natural extensions to other data-analysis techniques.",
"doi": "10.1016/j.jfluidstructs.2018.06.014",
"issn": "0889-9746",
"publisher": "Elsevier",
"publication": "Journal of Fluids and Structures",
"publication_date": "2018-08",
"volume": "81",
"pages": "728-737"
},
{
"id": "authors:bpq3j-0f809",
"collection": "authors",
"collection_id": "bpq3j-0f809",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180627-121240173",
"type": "article",
"title": "Spectral proper orthogonal decomposition and its relationship to dynamic mode decomposition and resolvent analysis",
"author": [
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We consider the frequency domain form of proper orthogonal decomposition (POD), called spectral proper orthogonal decomposition (SPOD). Spectral POD is derived from a space\u2013time POD problem for statistically stationary flows and leads to modes that each oscillate at a single frequency. This form of POD goes back to the original work of Lumley (Stochastic Tools in Turbulence, Academic Press, 1970), but has been overshadowed by a space-only form of POD since the 1990s. We clarify the relationship between these two forms of POD and show that SPOD modes represent structures that evolve coherently in space and time, while space-only POD modes in general do not. We also establish a relationship between SPOD and dynamic mode decomposition (DMD); we show that SPOD modes are in fact optimally averaged DMD modes obtained from an ensemble DMD problem for stationary flows. Accordingly, SPOD modes represent structures that are dynamic in the same sense as DMD modes but also optimally account for the statistical variability of turbulent flows. Finally, we establish a connection between SPOD and resolvent analysis. The key observation is that the resolvent-mode expansion coefficients must be regarded as statistical quantities to ensure convergent approximations of the flow statistics. When the expansion coefficients are uncorrelated, we show that SPOD and resolvent modes are identical. Our theoretical results and the overall utility of SPOD are demonstrated using two example problems: the complex Ginzburg\u2013Landau equation and a turbulent jet.",
"doi": "10.1017/jfm.2018.283",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2018-07-25",
"volume": "847",
"pages": "821-867"
},
{
"id": "authors:5tbgj-79030",
"collection": "authors",
"collection_id": "5tbgj-79030",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180711-155550672",
"type": "article",
"title": "Ensemble-Based State Estimator for Aerodynamic Flows",
"author": [
{
"family_name": "da Silva",
"given_name": "Andre F. C.",
"clpid": "da-Silva-A-F-C"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Regardless of the plant model, robust flow estimation based on limited measurements remains a major challenge in successful flow control applications. Aiming to combine the robustness of a high-dimensional representation of the dynamics with the cost efficiency of a low-order approximation of the state covariance matrix, a flow state estimator based on the ensemble Kalman filter is applied to two-dimensional flow past a cylinder and an airfoil at high angle of attack and low Reynolds number. For development purposes, the numerical algorithm is used as both the estimator and as a surrogate for the measurements. Estimation is successful using a reduced number of either pressure sensors on the surface of the body or sparsely placed velocity probes in the wake. Because the most relevant features of these flows are restricted to a low-dimensional manifold of the state space, asymptotic behavior of the estimator is shown to be achieved with a small ensemble size. The relative importance of each sensor location is evaluated by analyzing how they influence the estimated flowfield, and optimal locations for pressure sensors are determined. Covariance inflation is used to enhance the estimator performance in the presence of unmodeled freestream perturbations. A combination of parametric modeling and augmented state methodology is used to successfully estimate the forces on immersed bodies subjected to deterministic and random gusts.",
"doi": "10.2514/1.J056743",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2018-07",
"series_number": "7",
"volume": "56",
"issue": "7",
"pages": "2568-2578"
},
{
"id": "authors:vwchx-gez79",
"collection": "authors",
"collection_id": "vwchx-gez79",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059954",
"type": "conference_item",
"title": "Large-eddy simulations of co-annular turbulent jet using a Voronoi-based mesh generation framework",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Bose",
"given_name": "Sanjeeb T.",
"clpid": "Bose-S-T"
},
{
"family_name": "Emory",
"given_name": "Michael",
"clpid": "Emory-Michael"
},
{
"family_name": "Ham",
"given_name": "Frank E.",
"clpid": "Ham-Frank-E"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-G"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Large eddy simulations are performed for a cold ideally-expanded dual-stream jet issued from cylindrical co-axial nozzles, with supersonic primary stream (Mach number M_1 = 1.55) and subsonic secondary stream (M_2 = 0.9). The geometry includes the internal screw holes used to fasten the two nozzles together and to the plenum chamber. These slanted cylindrical holes over which the secondary stream flows were not covered in the experiment and were seamlessly captured in the computational mesh thanks to a novel grid generation paradigm based on the computation of Voronoi diagrams. A simulation with the screw holes covered is also performed and the preliminary results tends to indicate that these features have minimal impact on the flow and acoustic fields for the present operating conditions. As expected, the present dual-stream configuration with subsonic annular stream surrounding the primary supersonic stream features a reduced shear-layer growth, a longer potential core and a lack of strong Mach wave radiation. A long LES database is currently being collected for analysis and modeling of wavepackets and noise sources in such complex turbulent jets.",
"doi": "10.2514/6.2018-3302",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2018-06-24"
},
{
"id": "authors:n76h6-k0y88",
"collection": "authors",
"collection_id": "n76h6-k0y88",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059279",
"type": "conference_item",
"title": "A Bias-Aware EnKF Estimator for Aerodynamic Flows",
"author": [
{
"family_name": "da Silva",
"given_name": "Andre F.",
"clpid": "da-Silva-A-F-C"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Ensemble methods can integrate measurement data and CFD-based models to estimate the state of fluid systems in a robust and cost-efficient way. However, discretization errors can render numerical solutions a biased representation of reality. Left unaccounted for, biased forecast and observation models can lead to poor estimator performance. In this work, we propose a low-rank representation for the bias whose dynamics is represented by a colorednoise process. System state and bias parameters are simultaneously corrected on-line with the Ensemble Kalman Filter (EnKF) algorithm. The proposed methodology is demonstrated to achieve a 70% error reduction for the problem of estimating the state of the two-dimensional low-Re flow past a flat plate at high angle of attack using an ensemble of coarse-mesh simulations and pressure measurements at the surface of the body, compared to a bias-blind estimator. Strategies to determine the bias statistics and to deal with nonlinear observation functions in the context of ensemble methods are discussed.",
"doi": "10.2514/6.2018-3225",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2018-06-24"
},
{
"id": "authors:dktqz-77584",
"collection": "authors",
"collection_id": "dktqz-77584",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092058323",
"type": "conference_item",
"title": "Amplitude scaling of turbulent-jet wavepackets",
"author": [
{
"family_name": "Antonialli",
"given_name": "Luigi A.",
"clpid": "Antonialli-L-A"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "Wavepackets modelling large-scale coherent structures are related to the peak noise radiation by subsonic jets. Such wavepacket models are well developed in the literature, and are often based on a linearization of the Navier-Stokes system; solutions of the resulting linear problem have a free amplitude, which can be obtained by comparison with experiments or simulations. In this work we determine amplitudes of turbulent-jet wavepackets by comparing large-eddy simulation (LES) data from Br`es et al. of a Mach 0.9 jet and fluctuation fields using the parabolized stability equations (PSE) model (Sasaki et al.). Projection of the leading mode from spectral proper orthogonal decomposition (SPOD), applied to the LES data, onto the PSE model solutions is a way to determine the free amplitude, and by analyzing such amplitudes for different Strouhal numbers and azimuthal modes of the turbulent jet, it is possible to notice a clear pattern of the scaling factor with varying St. Azimuthal wavenumbers m = 0, 1 and 2 show an exponential dependence of wavepacket amplitude with Strouhal number. This sheds light on how wavepackets amplitudes behave and how they are excited upstream.",
"doi": "10.2514/6.2018-2978",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2018-06-24"
},
{
"id": "authors:2be44-74404",
"collection": "authors",
"collection_id": "2be44-74404",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180626-102029765",
"type": "article",
"title": "On the lift-optimal aspect ratio of a revolving wing at low Reynolds number",
"author": [
{
"family_name": "Jardin",
"given_name": "T.",
"orcid": "0000-0001-9704-2984",
"clpid": "Jardin-Thierry"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Lentink & Dickinson (2009 J. Exp. Biol. 212, 2705\u20132719. (doi:10.1242/jeb.022269)) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.",
"doi": "10.1098/rsif.2017.0933",
"pmcid": "PMC6030621",
"issn": "1742-5689",
"publisher": "Royal Society",
"publication": "Journal of the Royal Society Interface",
"publication_date": "2018-06",
"series_number": "143",
"volume": "15",
"issue": "143",
"pages": "Art. No. 20170933"
},
{
"id": "authors:mpa35-ghp95",
"collection": "authors",
"collection_id": "mpa35-ghp95",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092058933",
"type": "book_section",
"title": "Numerical Simulation of the Bubble Cloud Dynamics in an Ultrasound Field",
"book_title": "Proceedings of the 10th Symposium on Cavitation (CAV2018)",
"author": [
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "Katz",
"given_name": "Joseph",
"clpid": "Katz-J"
}
],
"abstract": "We use a coupled Eulerian-Lagrangian method to simulate the dynamics of a spherical bubble cloud with various void fractions excited by high-amplitude ultrasound pulses. We consider two cases: a single cycle of a sinusoidal waveform whose wavelength is large compared to the cloud diameter, and multiple cycles with a short wavelength. For the long wavelength, bubble cloud dynamics are nearly spherically symmetric. Bubbles near the periphery grow more than the those close to the center, and the collapse of bubbles propagates inward from the periphery of the cloud. The structure and the dynamics of the cloud are scaled with the cloud interaction parameter introduce by d'Agostino and Brennen. It is shown that polydispersity does not significantly alter the cloud dynamics. In the short wavelength case, the clouds develop an anisotropic structure in the direction of the incident wave propagation. Over a wide range of the void fraction, the distal side of the cloud is shielded from the incident wave and bubbles grow less. As characterized by the center of volume of the cloud, the anisotropy is similar over the range of volume fractions considered. The results of the study can be used to characterize the acoustic cavitation in ultrasound therapies.",
"doi": "10.1115/1.861851_ch151",
"isbn": "9780791861851",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "2018-05",
"pages": "795-800"
},
{
"id": "authors:52byp-d7r63",
"collection": "authors",
"collection_id": "52byp-d7r63",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102914",
"type": "book_section",
"title": "Investigation of the Energy Shielding of Kidney Stones by Cavitation Bubble Clouds during Burst Wave Lithotripsy",
"book_title": "Proceedings of the 10th Symposium on Cavitation (CAV2018)",
"author": [
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Maxwell",
"given_name": "Adam D.",
"clpid": "Maxwell-A-D"
},
{
"family_name": "Kreider",
"given_name": "Wayne",
"clpid": "Kreider-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-M-R"
}
],
"contributor": [
{
"family_name": "Katz",
"given_name": "Joseph",
"clpid": "Katz-J"
}
],
"abstract": "We conduct experiments and numerical simulations of the dynamics of bubble clouds nucleated on the surface of an epoxy cylindrical stone model during burst wave lithotripsy (BWL). In the experiment, the bubble clouds are visualized and bubble-scattered acoustics are measured. In the numerical simulation, we combine methods for modeling compressible multicomponent flows to capture complex interactions among cavitation bubbles, the stone, and the burst wave. Quantitative agreement is confirmed between results of the experiment and the simulation. We observe and quantify a significant shielding of incident wave energy by the bubble clouds. The magnitude of shielding reaches up to 80% of the total acoustic energy of the incoming burst wave, suggesting a potential loss of efficacy of stone comminution. We further discovered a strong linear correlation between the magnitude of the energy shielding and the amplitude of the bubble-scattered acoustics, independent of the initial size and the void fraction of bubble cloud within a range addressed in the simulation. This correlation could provide for real-time monitoring of cavitation activity in BWL.",
"doi": "10.1115/1.861851_ch119",
"isbn": "9780791861851",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "2018-05",
"pages": "626-630"
},
{
"id": "authors:pv7w5-gtm86",
"collection": "authors",
"collection_id": "pv7w5-gtm86",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100145",
"type": "book_section",
"title": "Transient Cavitation in Pre-Filled Syringes During Autoinjector Actuation",
"book_title": "Proceedings of the 10th Symposium on Cavitation (CAV2018)",
"author": [
{
"family_name": "Veilleux",
"given_name": "Jean-Christophe",
"orcid": "0000-0002-5420-9411",
"clpid": "Veilleux-J-C"
},
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Shepherd",
"given_name": "Joseph E.",
"orcid": "0000-0003-3181-9310",
"clpid": "Shepherd-J-E"
}
],
"contributor": [
{
"family_name": "Katz",
"given_name": "Joseph",
"clpid": "Katz-J"
}
],
"abstract": "Cavitation has been observed in the cone of a syringe actuated by an autoinjector device. Numerical simulations were used to determine if the cone can enhance the collapse of a bubble. We found the collapse of a bubble in a cone can be more violent than the collapse of a bubble close to a flat wall or in a free space due to the reflected wave focusing on the axis of symmetry.",
"doi": "10.1115/1.861851_ch203",
"isbn": "9780791861851",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "2018-05",
"pages": "1068-1073"
},
{
"id": "authors:mfh2h-99748",
"collection": "authors",
"collection_id": "mfh2h-99748",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100057",
"type": "book_section",
"title": "An Equation-of-State Tabulation Approach for Injectors with Non-Condensable Gases: Development and Analysis",
"book_title": "Proceedings of the 10th Symposium on Cavitation (CAV2018)",
"author": [
{
"family_name": "Bode",
"given_name": "Mathis",
"clpid": "Bode-Mathis"
},
{
"family_name": "Satcunanathan",
"given_name": "Sutharsan",
"clpid": "Satcunanathan-Sutharsan"
},
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Pitsch",
"given_name": "Heinz",
"clpid": "Pitsch-H"
}
],
"contributor": [
{
"family_name": "Katz",
"given_name": "Joseph",
"clpid": "Katz-J"
}
],
"abstract": "In this work, a general equation-of-state (EOS) tabulation method is presented, which allows arbitrary combinations of EOSs in different phases and can be used with single-phase flow solvers by adding one additional transport equation for the total partial density of all non-condensable gases. The new tabulation method assumes instantaneous equilibrium for all phase change processes and uses Legendre transformation to construct the convex hull of the energy surface. Newton iterations are applied to improve the accuracy within the tabulation step as well as of the data retrieved at runtime. A high-order 5-equation multiphase solver with stiffened-gas equations as EOS for all phases and with the ability to use different time scales for the relaxation processes between liquid and vapor phase is used to discuss the full equilibrium assumption of the tabulation approach. Furthermore, results using different EOSs for the tabulation are compared. The implication of choosing a stiffened-gas equation or a cubic EOS, such as the Peng Robinson equation for the vapor phase, on the saturation quantities is discussed. A nozzle simulation performed under typical gasoline direct injection (GDI) conditions is finally used to demonstrate the advantages of the new tabulation method and to evaluate additional computational cost.",
"doi": "10.1115/1.861851_ch10",
"isbn": "9780791861851",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "2018-05",
"pages": "45-50"
},
{
"id": "authors:wxgfm-r6z29",
"collection": "authors",
"collection_id": "wxgfm-r6z29",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102360",
"type": "conference_item",
"title": "Urinary stone erosion and fragmentation under low-intensity quasi-collimated ultrasound using gas-filled microbubbles with stone-targeting lipid shells",
"author": [
{
"family_name": "Pishchalnikov",
"given_name": "Yuri A.",
"clpid": "Pishchalnikov-Y-A"
},
{
"family_name": "Behnke-Parks",
"given_name": "William",
"clpid": "Behnke-Parks-W"
},
{
"family_name": "Mellema",
"given_name": "Matt",
"clpid": "Mellema-M"
},
{
"family_name": "Hopcroft",
"given_name": "Matt",
"clpid": "Hopcroft-M"
},
{
"family_name": "Luong",
"given_name": "Alice",
"clpid": "Luong-Alice"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Morrison",
"given_name": "Kyle",
"clpid": "Morrison-Kyle"
},
{
"family_name": "Laser",
"given_name": "Daniel",
"clpid": "Laser-D"
}
],
"abstract": "Urinary stone lithotripsy critically depends on the presence of cavitation nuclei at the stone surface. We hypothesized that introduction of stone-targeting microbubbles could increase cavitation activity at a stone surface sufficiently to allow stone erosion and fragmentation at peak negative pressures much lower than in acoustic energy-based urinary stone interventions with induced cavitation nuclei alone. Gas-filled microbubbles were produced with calcium-binding moieties incorporated into an encapsulating lipid shell. Stone surface coverage with these targeting microbubbles was found to approach an optimal (considering microbubble expansion during insonation) range of 5\u201315% with incubation times of three minutes or less. Using high-speed photomicroscopy, we observe bound microbubbles expanding 10- to 30-fold under insonation with quasi-collimated sources at mechanical indexes below 1.9. For observed stand-off parameters in the range of 0.2\u20130.6, the modeled collapse-generated shockwaves exceed 100 MPa. In swine model studies with these targeting microbubbles, stone fragmentation into passable fragments occurs with treatment times around 30 minutes, while post-treatment examination of ureters and kidneys shows no evidence of urothelium damage or renal parenchymal hemorrhage. The stone-targeting microbubbles reported on here have formed the basis for a new non-invasive urinary stone treatment which recently entered human clinical trials.",
"doi": "10.1121/1.5036106",
"publication_date": "2018-04-17"
},
{
"id": "authors:scr2s-cvy59",
"collection": "authors",
"collection_id": "scr2s-cvy59",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180329-105253706",
"type": "article",
"title": "Active Control of Noise from Hot Supersonic Jets",
"author": [
{
"family_name": "Sinha",
"given_name": "Aniruddha",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Schlinker",
"given_name": "Robert H.",
"clpid": "Schlinker-R-H"
},
{
"family_name": "Reba",
"given_name": "Ramons",
"clpid": "Reba-R"
},
{
"family_name": "Simonich",
"given_name": "John C.",
"clpid": "Simonich-J-C"
},
{
"family_name": "Shannon",
"given_name": "Daniel W.",
"clpid": "Shannon-D-W"
}
],
"abstract": "This paper presents diagnostic experiments aimed at understanding and mitigating supersonic jet noise from the coherent wave-packet structures that are the source of peak aft-angle mixing noise. Both isothermal and heated, nearly perfectly expanded, Mach 1.5 jets were forced in the near-nozzle region with air injection generated by a spinning-valve device designed to excite the jet at frequencies approaching those of the dominant turbulent structures. Substantial reductions in the peak aft-angle radiation were achieved with steady blowing at amplitudes corresponding to 2\u20136% of the mass flow rate of the primary jet. The noise benefit saturated at mass flow rates above 4%, with as much as a 6 dB reduction in overall sound pressure level at aft angles. Increasing the mass flow rates yielded a monotonically increasing high-frequency noise penalty at the sideline, where noise levels in the natural jet were already 15 dB lower than the aft-angle peak, so that the penalty due to actuation was minor. Although both steady and periodic unsteady mass injections were produced by the spinning valve when it rotated, it was calibrated to hold the steady mass flow rate constant as the frequency of unsteady blowing was changed. In this way, the effect of steady and unsteady blowings on the acoustic field could be decoupled. It is shown that the noise benefit was uniquely associated with the steady component of blowing, whereas the unsteady component resulted in additive tones in the spectra. This implied linearity is consistent with theory and experiments showing that the wave-packet structures, which give rise to the dominant aft-angle radiation, evolve in the turbulent mean flowfield in a nearly linear fashion from their origin in the near-nozzle region. The interpretation of noise reduction is that the steady component of blowing spreads the mean flow more rapidly, resulting in weaker wave packets. Periodic unsteady blowing forces coherent wave packets that are largely uncorrelated from the random natural ones, which then leads to the observed additive tones.",
"doi": "10.2514/1.J056159",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2018-03",
"series_number": "3",
"volume": "56",
"issue": "3",
"pages": "933-948"
},
{
"id": "authors:trxaf-xhg87",
"collection": "authors",
"collection_id": "trxaf-xhg87",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171220-135648871",
"type": "article",
"title": "Numerical simulation of the aerobreakup of a water droplet",
"author": [
{
"family_name": "Meng",
"given_name": "Jomela C.",
"orcid": "0000-0002-8966-2291",
"clpid": "Meng-Jomela-Chen-Chen"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We present a three-dimensional numerical simulation of the aerobreakup of a spherical water droplet in the flow behind a normal shock wave. The droplet and surrounding gas flow are simulated using the compressible multicomponent Euler equations in a finite-volume scheme with shock and interface capturing. The aerobreakup process is compared with available experimental visualizations. Features of the droplet deformation and breakup in the stripping breakup regime, as well as descriptions of the surrounding gas flow, are discussed. Analyses of observed surface instabilities and a Fourier decomposition of the flow field reveal asymmetrical azimuthal modulations and broadband instability growth that result in chaotic flow within the wake region.",
"doi": "10.1017/jfm.2017.804",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2018-01-25",
"volume": "835",
"pages": "1108-1135"
},
{
"id": "authors:4bwxh-z4k62",
"collection": "authors",
"collection_id": "4bwxh-z4k62",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059362",
"type": "conference_item",
"title": "EnKF-Based Dynamic Estimation of Separated Flows with a Low-Order Vortex Model",
"author": [
{
"family_name": "Darakananda",
"given_name": "Darwin",
"clpid": "Darakananda-D"
},
{
"family_name": "Eldredge",
"given_name": "Jeff",
"clpid": "Eldredge-J-D"
},
{
"family_name": "da Silva",
"given_name": "Andre",
"clpid": "da-Silva-A-F-C"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
}
],
"abstract": "A data-driven vortex model of the unsteady aerodynamics of a two-dimensional separated flow is constructed. The vortex model relies on a standard collection of regularized vortex elements that interact mutually and with an infinitely-thin flat plate. In order to maintain a low-dimensional representation, with fewer than O(100) degrees of freedom, a novel aggregation procedure is developed and utilized in which vortex elements are coalesced at each time step. A flow state vector, composed of vortex elements properties as well as the critical leading-edge suction parameter of Ramesh and Gopalarathnam (J. Fluid Mech., 2014), is advanced within an ensemble Kalman filter (EnKF) framework. In this framework, surface pressure measurements, sampled from a truth case, are used to correct the states of an ensemble of randomly-initiated vortex element models. The estimation algorithm is applied to several scenarios of a flat plate impulsively started at 20 degrees angle of attack at Reynolds number 500, in which the truth case comprises a high-fidelity Navier\u2013Stokes simulation. The algorithm provides a good estimate of the flow as well as the aerodynamic force in both the baseline undisturbed case (a separated flow) as well as in the presence of one or more incident gusts, despite lack of a priori knowledge of the incident gust character.",
"doi": "10.2514/6.2018-0811",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2018-01-07"
},
{
"id": "authors:x9qxf-tja52",
"collection": "authors",
"collection_id": "x9qxf-tja52",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171201-152324924",
"type": "article",
"title": "Experimental study of turbulent-jet wave packets and their acoustic efficiency",
"author": [
{
"family_name": "Breakey",
"given_name": "David E. S.",
"clpid": "Breakey-D-E-S"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Nogueira",
"given_name": "Petr\u00f4nio A.",
"clpid": "Nogueira-P-A"
},
{
"family_name": "L\u00e9on",
"given_name": "Olivier",
"clpid": "L\u00e9on-O"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Rodr\u00edguez",
"given_name": "Daniel",
"clpid": "Rodr\u00edguez-D"
}
],
"abstract": "This paper details the statistical and time-resolved analysis of the relationship between the near-field pressure fluctuations of unforced, subsonic free jets (0.4 \u2264 M \u2264 0.6) and their far-field sound emissions. Near-field and far-field microphone measurements were taken on a conical array close to the jets and an azimuthal ring at 20\u2218 to the jet axis, respectively. Recent velocity and pressure measurements indicate the presence of linear wave packets in the near field by closely matching predictions from the linear homogenous parabolized stability equations, but the agreement breaks down both beyond the end of the potential core and when considering higher order statistical moments, such as the two-point coherence. Proper orthogonal decomposition (POD), interpreted in terms of inhomogeneous linear models using the resolvent framework allows us to understand these discrepancies. A new technique is developed for projecting time-domain pressure measurements onto a statistically obtained POD basis, yielding the time-resolved activity of each POD mode and its correlation with the far field. A single POD mode, interpreted as an optimal high-gain structure that arises due to turbulent forcing, captures the salient near-field\u2013far-field correlation signature; further, the signatures of the next two modes, understood as suboptimally forced structures, suggest that these POD modes represent higher order, acoustically important near-field behavior. An existing Green's-function-based technique is used to make far-field predictions, and results are interpreted in terms of POD/resolvent modes, indicating the acoustic importance of this higher order behavior. The technique is extended to provide time-domain far-field predictions.",
"doi": "10.1103/PhysRevFluids.2.124601",
"issn": "2469-990X",
"publisher": "American Physical Society",
"publication": "Physical Review Fluids",
"publication_date": "2017-12",
"series_number": "12",
"volume": "2",
"issue": "12",
"pages": "Art. No. 124601"
},
{
"id": "authors:q7fn7-mdy41",
"collection": "authors",
"collection_id": "q7fn7-mdy41",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171213-075938896",
"type": "article",
"title": "Modal Analysis of Fluid Flows: An Overview",
"author": [
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
},
{
"family_name": "Brunton",
"given_name": "Steven L.",
"clpid": "Brunton-S-L"
},
{
"family_name": "Dawson",
"given_name": "Scott T. M.",
"orcid": "0000-0002-0020-2097",
"clpid": "Dawson-S-T-M"
},
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "McKeon",
"given_name": "Beverley J.",
"orcid": "0000-0003-4220-1583",
"clpid": "McKeon-B-J"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Gordeyev",
"given_name": "Stanislav",
"clpid": "Gordeyev-S"
},
{
"family_name": "Theofilis",
"given_name": "Vassilios",
"clpid": "Theofilis-V"
},
{
"family_name": "Ukeiley",
"given_name": "Lawrence S.",
"clpid": "Ukeiley-L-S"
}
],
"abstract": "Simple aerodynamic configurations under even modest conditions can exhibit complex flows with a wide range of temporal and spatial features. It has become common practice in the analysis of these flows to look for and extract physically important features, or modes, as a first step in the analysis. This step typically starts with a modal decomposition of an experimental or numerical dataset of the flowfield, or of an operator relevant to the system. We describe herein some of the dominant techniques for accomplishing these modal decompositions and analyses that have seen a surge of activity in recent decades [1\u20138]. For a nonexpert, keeping track of recent developments can be daunting, and the intent of this document is to provide an introduction to modal analysis that is accessible to the larger fluid dynamics community. In particular, we present a brief overview of several of the well-established techniques and clearly lay the framework of these methods using familiar linear algebra. The modal analysis techniques covered in this paper include the proper orthogonal decomposition (POD), balanced proper orthogonal decomposition (balanced POD), dynamic mode decomposition (DMD), Koopman analysis, global linear stability analysis, and resolvent analysis.",
"doi": "10.2514/1.J056060",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2017-12",
"series_number": "12",
"volume": "55",
"issue": "12",
"pages": "4013-4041"
},
{
"id": "authors:1jcgf-xyj41",
"collection": "authors",
"collection_id": "1jcgf-xyj41",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170912-144135521",
"type": "article",
"title": "A source term approach for generation of one-way acoustic waves in the Euler and Navier\u2013Stokes equations",
"author": [
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We derive a volumetric source term for the Euler and Navier\u2013Stokes equations that mimics the generation of unidirectional acoustic waves from an arbitrary smooth surface in three-dimensional space. The model is constructed as a linear combination of monopole and dipole sources in the mass, momentum, and energy equations. The singular source distribution on the surface is regularized on a computational grid by convolution with a smeared Dirac delta function. The source is implemented in the Euler equations using a Cartesian-grid finite-volume WENO scheme, and validated by comparing with analytical solution for unidirectional planar and spherical acoustic waves. Using the scheme, we emulate a spherical piezoelectric transducer and a multi-array transducer to simulate focused ultrasound fields in water. The simulated ultrasound fields show favorable agreement with previous experiments.",
"doi": "10.1016/j.wavemoti.2017.08.004",
"pmcid": "PMC6159925",
"issn": "0165-2125",
"publisher": "Elsevier",
"publication": "Wave Motion",
"publication_date": "2017-12",
"volume": "75",
"pages": "36-49"
},
{
"id": "authors:xs8a9-qk853",
"collection": "authors",
"collection_id": "xs8a9-qk853",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171006-075054128",
"type": "article",
"title": "Special issue on global flow instability and control",
"author": [
{
"family_name": "Sharma",
"given_name": "Ati",
"orcid": "0000-0002-7170-1627",
"clpid": "Sharma-A-S"
},
{
"family_name": "Theofilis",
"given_name": "Vassilis",
"clpid": "Theofilis-V"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "This special issue is the second on the topic of \"Global Flow Instability and Control,\" following the first in 2011. As with the previous special issue, the participants of the last two symposia on Global Flow Instability and Control, held in Crete, Greece, were invited to submit publications. These papers were peer reviewed according to the standards of the journal, and this issue represents a snapshot of the progress since 2011. In this preface, a sampling of important developments in the field since the first issue is discussed. A synopsis of the papers in this issue is given in that context.",
"doi": "10.1007/s00162-017-0444-y",
"issn": "0935-4964",
"publisher": "Springer",
"publication": "Theoretical and Computational Fluid Dynamics",
"publication_date": "2017-12",
"series_number": "5-6",
"volume": "31",
"issue": "5-6",
"pages": "471-474"
},
{
"id": "authors:sp6dy-37s98",
"collection": "authors",
"collection_id": "sp6dy-37s98",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171020-092303673",
"type": "article",
"title": "High-frequency wavepackets in turbulent jets",
"author": [
{
"family_name": "Sasaki",
"given_name": "Kenzo",
"orcid": "0000-0002-3347-4996",
"clpid": "Sasaki-Kenzo"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "Wavepackets obtained as solutions of the flow equations linearised around the mean flow have been shown in recent work to yield good agreement, in terms of amplitude and phase, with those educed from turbulent jets. Compelling agreement has been demonstrated, for the axisymmetric and first helical mode, up to Strouhal numbers close to unity. We here extend the range of validity of wavepacket models to Strouhal number St = 4.0 and azimuthal wavenumber m = 4 by comparing solutions of the parabolised stability equations with a well-validated large-eddy simulation of a Mach 0.9 turbulent jet. The results show that the near-nozzle dynamics can be correctly described by the homogeneous linear model, the initial growth rates being accurately predicted for the entire range of frequencies and azimuthal wavenumbers considered. Similarly to the lower-frequency wavepackets reported prior to this work, the high-frequency linear waves deviate from the data downstream of their stabilisation locations, which move progressively upstream as the frequency increases.",
"doi": "10.1017/jfm.2017.659",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2017-11-10",
"volume": "830",
"pages": "Art. No. R2"
},
{
"id": "authors:hkfxm-jrc87",
"collection": "authors",
"collection_id": "hkfxm-jrc87",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170818-081556658",
"type": "article",
"title": "Acoustic resonance in the potential core of subsonic jets",
"author": [
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Schmidt",
"given_name": "Oliver",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Jaunet",
"given_name": "Vincent",
"clpid": "Jaunet-V"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "The purpose of this paper is to characterize and model waves that are observed within the potential core of subsonic jets and relate them to previously observed tones in the near-nozzle region. The waves are detected in data from a large-eddy simulation of a Mach 0.9 isothermal jet and modelled using parallel and weakly non-parallel linear modal analysis of the Euler equations linearized about the turbulent mean flow, as well as simplified models based on a cylindrical vortex sheet and the acoustic modes of a cylindrical soft duct. In addition to the Kelvin\u2013Helmholtz instability waves, three types of waves with negative phase velocities are identified in the potential core: upstream- and downstream-propagating duct-like acoustic modes that experience the shear layer as a pressure-release surface and are therefore radially confined to the potential core, and upstream-propagating acoustic modes that represent a weak coupling between the jet core and the free stream. The slow streamwise contraction of the potential core imposes a frequency-dependent end condition on the waves that is modelled as the turning points of a weakly non-parallel approximation of the waves. These turning points provide a mechanism by which the upstream- and downstream-travelling waves can interact and exchange energy through reflection and transmission processes. Paired with a second end condition provided by the nozzle, this leads to the possibility of resonance in limited frequency bands that are bound by two saddle points in the complex wavenumber plane. The predicted frequencies closely match the observed tones detected outside of the jet. The vortex-sheet model is then used to systematically explore the Mach number and temperature ratio dependence of the phenomenon. For isothermal jets, the model suggests that resonance is likely to occur in a narrow range of Mach number, 0.82 < M < 1.",
"doi": "10.1017/jfm.2017.346",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2017-08-25",
"volume": "825",
"pages": "1113-1152"
},
{
"id": "authors:drycm-54814",
"collection": "authors",
"collection_id": "drycm-54814",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170818-083639884",
"type": "article",
"title": "Wavepackets and trapped acoustic modes in a turbulent jet: coherent structure eduction and global stability",
"author": [
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "Coherent features of a turbulent Mach 0.9, Reynolds number 10^6 jet are educed from a high-fidelity large eddy simulation. Besides the well-known Kelvin\u2013Helmholtz instabilities of the shear layer, a new class of trapped acoustic waves is identified in the potential core. A global linear stability analysis based on the turbulent mean flow is conducted. The trapped acoustic waves form branches of discrete eigenvalues in the global spectrum, and the corresponding global modes accurately match the educed structures. Discrete trapped acoustic modes occur in a hierarchy determined by their radial and axial order. A local dispersion relation is constructed from the global modes and found to agree favourably with an empirical dispersion relation educed from the simulation data. The product between direct and adjoint modes is then used to isolate the trapped waves. Under certain conditions, resonance in the form of a beating occurs between trapped acoustic waves of positive and negative group velocities. This resonance explains why the trapped modes are prominently observed in the simulation and as tones in previous experimental studies. In the past, these tones were attributed to external factors. Here, we show that they are an intrinsic feature of high-subsonic jets that can be unambiguously identified by a global linear stability analysis.",
"doi": "10.1017/jfm.2017.407",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2017-08-25",
"volume": "825",
"pages": "1153-1181"
},
{
"id": "authors:7agx4-byg45",
"collection": "authors",
"collection_id": "7agx4-byg45",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059193",
"type": "conference_item",
"title": "A global mode analysis of flapping flags",
"author": [
{
"family_name": "Goza",
"given_name": "Andres",
"orcid": "0000-0002-9372-7713",
"clpid": "Goza-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We perform a global stability analysis of a flapping flag in the conventional configuration, in which the flag is pinned or clamped at its leading edge, and in the inverted configuration, in which the flag is clamped at its trailing edge. Specifically, we consider fully coupled fluid-structure interaction for two-dimensional flags at low Reynolds numbers. For the conventional configuration, we show that the unstable global modes accurately predict the onset of flapping for a wide range of mass and stiffness ratios. For the inverted configuration, we identify a stable deformed equilibrium state and demonstrate that as the flag becomes less stiff, this equilibrium undergoes a supercritical Hopf bifurcation in which the least damped mode transitions to instability. Previous stability analyses of inverted flags computed the leading mode of the undeformed equilibrium state and found it to be a zero-frequency (non-flapping) mode, which does not reflect the inherent flapping behavior. We show that the leading mode of the deformed equilibrium is associated with a non-zero frequency, and therefore offers a mechanism for flapping. We emphasize that for both configurations the global modes are obtained from the fully-coupled flow-flag system, and therefore reveal both the most dominant flag shapes and the corresponding flow structures that are pivotal to flag flapping behavior.",
"publisher": "Begel House Inc.",
"publication_date": "2017-07"
},
{
"id": "authors:7abkv-d0937",
"collection": "authors",
"collection_id": "7abkv-d0937",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102823",
"type": "conference_item",
"title": "Ed Carstensen, advisor and mentor to the shockwave lithotripsy program project group",
"author": [
{
"family_name": "McAteer",
"given_name": "James",
"clpid": "McAteer-J-A"
},
{
"family_name": "Evan",
"given_name": "Andrew P.",
"clpid": "Evan-A-P"
},
{
"family_name": "Lingeman",
"given_name": "James E.",
"clpid": "Lingeman-J-E"
},
{
"family_name": "Willis",
"given_name": "Lynn R.",
"clpid": "Willis-L-R"
},
{
"family_name": "Blomgren",
"given_name": "Philip M.",
"clpid": "Blomgren-P-M"
},
{
"family_name": "Williams",
"given_name": "James C.",
"clpid": "Williams-J-C-Jr"
},
{
"family_name": "Handa",
"given_name": "Rajash",
"clpid": "Handa-Rajash"
},
{
"family_name": "Connors",
"given_name": "Bret A.",
"clpid": "Connors-B-A"
},
{
"family_name": "Crum",
"given_name": "Lawrence",
"clpid": "Crum-L-A"
},
{
"family_name": "Bailey",
"given_name": "Michael",
"clpid": "Bailey-M-R"
},
{
"family_name": "Matula",
"given_name": "Tom",
"clpid": "Matula-Tom"
},
{
"family_name": "Khokhlova",
"given_name": "Vera A.",
"clpid": "Khokhlova-Vera"
},
{
"family_name": "Sapozhnikov",
"given_name": "Oleg A.",
"clpid": "Sapozhnikov-O-A"
},
{
"family_name": "Cleveland",
"given_name": "Robin",
"clpid": "Cleveland-R-O"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Pishchalnikov",
"given_name": "Yuri A.",
"clpid": "Pishchalnikov-Y-A"
}
],
"abstract": "In the 1980s shockwave lithotripsy emerged as a revolutionary advancement for the treatment of kidney stones. Initial studies with patients showed SWL to be highly effective. The technology was elegant, outcomes exceptionally positive and early tests suggested treatment was safe. As experience with SWL grew, limitations surfaced. A key finding was that SWs have the potential to induce significant trauma to the kidney. Our group convinced the NIH it was time to conduct a rigorous assessment to characterize the adverse effects of SWL and determine the mechanisms of SW action in stone breakage and tissue injury. The NIH Program Project Grant mechanism mandated we establish a panel of external advisors to help guide our work. We needed expertise in physical acoustics, cavitation and animal models of ultrasound exposure. We wanted a leading expert. We were extremely fortunate to land Ed Carstensen. Ed worked with us for nearly 15 years, well into our third renewal cycle. He was a brilliant scientist, a man dedicated to the highest standards of conduct in research. Ed taught us a great deal, he inspired by example and had an exceptional influence on our work and on the greater field of lithotripsy research.",
"doi": "10.1121/1.4988642",
"publisher": "ASA",
"publication_date": "2017-06-10"
},
{
"id": "authors:qrbvv-tcw85",
"collection": "authors",
"collection_id": "qrbvv-tcw85",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092058839",
"type": "conference_item",
"title": "Quantification of the shielding of kidney stones by bubble clouds during burst wave lithotripsy",
"author": [
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Kreider",
"given_name": "Wayne",
"clpid": "Kreider-W"
},
{
"family_name": "Maxwell",
"given_name": "Adam D.",
"clpid": "Maxwell-A-D"
},
{
"family_name": "Bailey",
"given_name": "Michael",
"clpid": "Bailey-M-R"
}
],
"abstract": "Bubble clouds can shield kidney stones from insonification, and limit stone breakage during burst-wave lithotripsy (BWL), a recently proposed technique that uses focused ultrasound pulses with an amplitude of O(1-10) MPa and frequency of O(0.1) MHz. We use numerical simulations to quantify the magnitude of such shielding. In the simulations, we solve for the radial evolution of Lagrangian bubbles coupled to a compressible fluid using volume-averaging techniques. The resulting equations are discretized on an Eulerian grid. In particular, we quantify the reduction in acoustic energy flux incident on a rigid, plane wall that models the stone surface. We consider a burst wave with an amplitude of 6 MPa and a bubble cloud of diameter O(1) mm. The size distribution of nuclei, the number density of bubbles, and the distance of the cloud from the wall are varied, We show that a cloud containing O(10) bubbles with a diameter of O(10) um can reduce the total energy flux by more than 50%, largely independent of distribution of nuclei. Finally, we compare the simulation results with high-speed images and hydrophone measurements of bubble clouds from companion experiments.",
"doi": "10.1121/1.4987968",
"publisher": "Acoustical Society of America",
"publication_date": "2017-06-09"
},
{
"id": "authors:a9827-z2533",
"collection": "authors",
"collection_id": "a9827-z2533",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100532",
"type": "conference_item",
"title": "An EnKF-Based Flow State Estimator for Aerodynamic Flows",
"author": [
{
"family_name": "da Silva",
"given_name": "Andre F. C.",
"clpid": "da-Silva-A-F-C"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Regardless of plant model, robust flow estimation based on limited measurements remains a major obstacle to successful flow control applications. Aiming to combine the robustness of a high-dimensional representation of the dynamics with the cost efficiency of a low-order approximation of the state covariance matrix, a flow state estimator based on the Ensemble Kalman Filter (EnKF) is applied to two-dimensional flow past a cylinder and an airfoil at high angle of attack and low Reynolds number. For the development purposes, we use the numerical algorithm as both the estimator and as a surrogate for the measurements. Estimation is successful using a reduced number of either pressure sensors on the surface of the body or sparsely placed velocity probes in the wake. Because the most relevant features of these flows is restricted to a low-dimensional subspace/manifold of the state space, asymptotic behavior of the estimator is shown to be achieved with a small ensemble size. The relative importance of each sensor location is evaluated by analyzing how they influence the estimated flow field. Covariance inflation is used to enhance the estimator performance in the presence of unmodeled free stream perturbations. A combination of parametric modeling and augmented state methodology is used to successfully estimate the forces on immersed bodies.",
"doi": "10.2514/6.2017-3483",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2017-06-07"
},
{
"id": "authors:dsj7w-7kr08",
"collection": "authors",
"collection_id": "dsj7w-7kr08",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102731",
"type": "conference_item",
"title": "Immersed Boundary Lattice Green Function methods for External Aerodynamics",
"author": [
{
"family_name": "Mengaldo",
"given_name": "Gianmarco",
"orcid": "0000-0002-0157-5477",
"clpid": "Mengaldo-Gianmarco"
},
{
"family_name": "Liska",
"given_name": "Sebastian",
"orcid": "0000-0003-4139-9364",
"clpid": "Liska-Sebastian"
},
{
"family_name": "Yu",
"given_name": "Ke",
"orcid": "0000-0003-0157-4471",
"clpid": "Yu-Ke"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Jardin",
"given_name": "Thierry",
"clpid": "Jardin-Thierry"
}
],
"abstract": "In this paper, we document the capabilities of a novel numerical approach \u2014 the immersed boundary lattice Green's function (IBLGF) method \u2014 to simulate external incompressible flows over complex geometries. This new approach is built upon the immersed boundary method and lattice Green's functions to solve the incompressible Navier-Stokes equations. We show that the combination of these two concepts allows the construction of an efficient and robust numerical framework for the direct numerical and large-eddy simulation of external aerodynamic problems at moderate to high-Reynolds numbers.",
"doi": "10.2514/6.2017-3621",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2017-06-02"
},
{
"id": "authors:q5r6j-xgp17",
"collection": "authors",
"collection_id": "q5r6j-xgp17",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092058182",
"type": "conference_item",
"title": "Response of the Separated Flow over an Airfoil to a Short-Time Actuator Burst",
"author": [
{
"family_name": "An",
"given_name": "Xuanhong",
"clpid": "An-Xuanhong"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
},
{
"family_name": "de Castro da Silva",
"given_name": "Andr\u00e9 Fernando",
"clpid": "de-Castro-da-Silva-A-F"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Eldredge",
"given_name": "Jeff D.",
"clpid": "Eldredge-J-D"
}
],
"abstract": "Experimental measurements of the flow structure evolving in the separated flow over an NACA 0009 wing at 12\u00b0 angle of attack were obtained with particle image velocimetry, surface pressures, and force transducer measurements of the lift coefficient and pitching moment coefficient. Phase-averaged two-dimensional velocity field measurements provide details of the separated shear layer evolution following a four-pulse burst sequence from a synthetic jet actuator. The flow field development is quite similar to the observations made by Brzozowski, et al. (2010), who used a pulsed-combustion actuator that is orders of magnitude stronger than the synthetic jet. Proper orthogonal decomposition of the PIV data sets showed that the combination of the time-varying coefficients modes 1 and 2 correlate with the negative of the lift coefficient response. The surface pressure signals were correlated with the roll up and convection of the large-scale vortex structure that follows the actuator burst input. A spatially localized region of high pressure occurs below and slightly behind a \"kink\" that forms in the shear layer. A localized region of high surface pressure that follows the kinked region correlates with the lift reversal that occurs within 2.0t^+ after the burst signal was triggered.",
"doi": "10.2514/6.2017-3315",
"publisher": "american institute of aeronautics and astronautics",
"publication_date": "2017-06-02"
},
{
"id": "authors:9wndm-trf85",
"collection": "authors",
"collection_id": "9wndm-trf85",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059023",
"type": "conference_item",
"title": "Evaluation of PSE as a Model for Supersonic Jet Using Transfer Functions",
"author": [
{
"family_name": "Kleine",
"given_name": "Vitor G.",
"clpid": "Kleine-V-G"
},
{
"family_name": "Sasaki",
"given_name": "Kenzo",
"orcid": "0000-0002-3347-4996",
"clpid": "Sasaki-Kenzo"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Parabolized Stability Equations (PSE) have been shown to model wavepackets and, consequently, the near field of turbulent jets with reasonable accuracy. Because of these capabilities, PSE is a promising reduced-order model to derive control laws that could be employed to reduce the sound generation of a jet. The purpose of this work is to apply PSE to obtain time-domain transfer functions that could estimate both the fluid-dynamic and the acoustic fields of a supersonic jet. The results of this model were compared to results obtained from a database of a well-validated large-eddy simulation of a supersonic jet.\n\nBased on the unsteady pressure data at a input position, the time-domain pressure field was estimated using transfer functions obtained using PSE and an empirical method based on the LES data. The prediction scheme employed is a single-input-single-output (SISO), linear model. The unsteady pressure predicted by PSE showed good agreement with the LES results, especially if the input position is outside the mixing layer. For this region, the prediction capabilities of PSE are comparable to those of empirical transfer functions. The agreement is good even for output points taken in the acoustic field, showing that it is possible to estimate the time-domain behaviour of Mach-wave radiation using transfer functions.\n\nThis indicates that PSE could not only be used to predict the sound generation, but also to open up new potentialities to attenuate noise by means of closed-loop control of the flow. The exploration of the regions where the method displayed good agreement, presented in this work, can guide the positioning of sensors and actuators for experimental implementation of closed-loop control in a jet.",
"doi": "10.2514/6.2017-4194",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2017-06-02"
},
{
"id": "authors:kw7v0-nn045",
"collection": "authors",
"collection_id": "kw7v0-nn045",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092101985",
"type": "conference_item",
"title": "One Way Navier-Stokes and resolvent analysis for modeling coherent structures in a supersonic turbulent jet",
"author": [
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-G"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "A linear analysis of the mean flow of an isothermal ideally-expanded Mach 1.5 turbulent jet is conducted. Optimal response modes describing the fluctuating hydrodynamic and acoustic fields are obtained in a computationally efficient way by spatially marching the linearized One-Way Navier-Stokes equations. For this purpose, an adjoint-based optimization framework is proposed and demonstrated for calculating optimal boundary conditions and optimal volumetric forcing. The optimal modes are validated against modes obtained in terms of global resolvent analysis. Two scenarios are considered in the present analysis. In the first case, no restrictions are applied to the spatial forcing distribution. In the second scenario, the forcing is restricted to the nozzle plane. The resulting optimal and suboptimal modes are compared to spectral proper orthogonal modes obtained from a high-fidelity large eddy simulation. The implications of these observations are discussed in detail.",
"doi": "10.2514/6.2017-4046",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2017-06-02"
},
{
"id": "authors:kd90d-fwg72",
"collection": "authors",
"collection_id": "kd90d-fwg72",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161114-103855929",
"type": "article",
"title": "A strongly-coupled immersed-boundary formulation for thin elastic structures",
"author": [
{
"family_name": "Goza",
"given_name": "Andres",
"orcid": "0000-0002-9372-7713",
"clpid": "Goza-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We present a strongly-coupled immersed-boundary method for flow\u2013structure interaction problems involving thin deforming bodies. The method is stable for arbitrary choices of solid-to-fluid mass ratios and for large body motions. As with many strongly-coupled immersed-boundary methods, our method requires the solution of a nonlinear algebraic system at each time step. The system is solved through iteration, where the iterates are obtained by linearizing the system and performing a block-LU factorization. This restricts all iterations to small-dimensional subsystems that scale with the number of discretization points on the immersed surface, rather than on the entire flow domain. Moreover, the iteration procedure we propose does not involve heuristic regularization parameters, and has converged in a small number of iterations for all problems we have considered. We derive our method for general deforming surfaces, and verify the method with two-dimensional test problems of geometrically nonlinear flags undergoing large amplitude flapping behavior.",
"doi": "10.1016/j.jcp.2017.02.027",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2017-05-01",
"volume": "336",
"pages": "401-411"
},
{
"id": "authors:47prs-qw090",
"collection": "authors",
"collection_id": "47prs-qw090",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190708-164305356",
"type": "conference_item",
"title": "Innovative strategies for improved outcomes in nephrolithiasis",
"author": [
{
"family_name": "Bailey",
"given_name": "Michael",
"clpid": "Bailey-M-R"
},
{
"family_name": "Simon",
"given_name": "Julianna C.",
"clpid": "Simon-Julianna-C"
},
{
"family_name": "Kreider",
"given_name": "Wayne",
"clpid": "Kreider-W"
},
{
"family_name": "Dunmire",
"given_name": "Barbrina",
"clpid": "Dunmire-Barbrina"
},
{
"family_name": "Crum",
"given_name": "Lawrence",
"clpid": "Crum-L-A"
},
{
"family_name": "Maxwell",
"given_name": "Adam D.",
"clpid": "Maxwell-A-D"
},
{
"family_name": "Khokhlova",
"given_name": "Vera",
"clpid": "Khokhlova-Vera"
},
{
"family_name": "Sapozhnikov",
"given_name": "Oleg A.",
"clpid": "Sapozhnikov-O-A"
},
{
"family_name": "Cleveland",
"given_name": "Robin",
"clpid": "Cleveland-R-O"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lingeman",
"given_name": "James E.",
"clpid": "Lingeman-J-E"
},
{
"family_name": "McAteer",
"given_name": "James",
"clpid": "McAteer-J-A"
},
{
"family_name": "Williams",
"given_name": "James C.",
"clpid": "Williams-J-C-Jr"
},
{
"family_name": "Freund",
"given_name": "Jonathan",
"clpid": "Freund-J-B"
}
],
"abstract": "Edwin Carstensen, Ph.D., was an advisor of NIH NIDDK Program Project Grant DK043881, created to investigate shock wave lithotripsy (SWL). We now develop solutions to improve all aspects of the management of stone disease. Our goal in this paper is to report progress built on Dr. Cartsensen's advice and inspiration. The work ranges from numerical simulation to clinical trials and from device development to bioeffects and metrology. Much of our work involves bubbles and cavitation. This work has contributed to the body of knowledge defining limits for the safe use of ultrasound which Dr. Carstensen worked hard to establish. Specifically, an update will be given on the development of ultrasound to image, fragment, trap, and reposition stones. In particular, we demonstrated bubbles contribute to the twinkling artifact used by NASA and others to image stones, and we drew on Dr. Carstensen's paper [UMB, 19(2) 147-165 1993] to demonstrate that breathing the elevated carbon dioxide levels present in NASA vehicles suppresses this signal making stone imaging more difficult. We have since developed imaging countermeasures and pushing and breaking technologies that appear less dependent on cavitation than SWL.",
"doi": "10.1121/1.4988643",
"publisher": "Acoustical Society of America",
"publication_date": "2017-05"
},
{
"id": "authors:9q6es-f5z32",
"collection": "authors",
"collection_id": "9q6es-f5z32",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161219-080814106",
"type": "article",
"title": "A fast immersed boundary method for external incompressible viscous flows using lattice Green's functions",
"author": [
{
"family_name": "Liska",
"given_name": "Sebastian",
"orcid": "0000-0003-4139-9364",
"clpid": "Liska-S"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "A new parallel, computationally efficient immersed boundary method for solving three-dimensional, viscous, incompressible flows on unbounded domains is presented. Immersed surfaces with prescribed motions are generated using the interpolation and regularization operators obtained from the discrete delta function approach of the original (Peskin's) immersed boundary method. Unlike Peskin's method, boundary forces are regarded as Lagrange multipliers that are used to satisfy the no-slip condition. The incompressible Navier\u2013Stokes equations are discretized on an unbounded staggered Cartesian grid and are solved in a finite number of operations using lattice Green's function techniques. These techniques are used to automatically enforce the natural free-space boundary conditions and to implement a novel block-wise adaptive grid that significantly reduces the run-time cost of solutions by limiting operations to grid cells in the immediate vicinity and near-wake region of the immersed surface. These techniques also enable the construction of practical discrete viscous integrating factors that are used in combination with specialized half-explicit Runge\u2013Kutta schemes to accurately and efficiently solve the differential algebraic equations describing the discrete momentum equation, incompressibility constraint, and no-slip constraint. Linear systems of equations resulting from the time integration scheme are efficiently solved using an approximation-free nested projection technique. The algebraic properties of the discrete operators are used to reduce projection steps to simple discrete elliptic problems, e.g. discrete Poisson problems, that are compatible with recent parallel fast multipole methods for difference equations. Numerical experiments on low-aspect-ratio flat plates and spheres at Reynolds numbers up to 3700 are used to verify the accuracy and physical fidelity of the formulation.",
"doi": "10.1016/j.jcp.2016.11.034",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2017-02-15",
"volume": "331",
"pages": "257-279"
},
{
"id": "authors:hyvtg-k9w41",
"collection": "authors",
"collection_id": "hyvtg-k9w41",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170407-133420635",
"type": "article",
"title": "Transition to bluff-body dynamics in the wake of vertical-axis wind turbines",
"author": [
{
"family_name": "Araya",
"given_name": "Daniel B.",
"clpid": "Arayba-D-B"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Dabiri",
"given_name": "John O.",
"orcid": "0000-0002-6722-9008",
"clpid": "Dabiri-J-O"
}
],
"abstract": "We present experimental data to demonstrate that the far wake of a vertical-axis wind turbine (VAWT) exhibits features that are quantitatively similar to that of a circular cylinder with the same aspect ratio. For a fixed Reynolds number (Re \u2248 0.8 \u00d7 10^5) and variable tip-speed ratio, two-dimensional particle image velocimetry (PIV) is used to measure the velocity field in the wake of four different laboratory-scale models: a 2-bladed, 3-bladed and 5-bladed VAWT, as well as a circular cylinder. With these measurements, we use spectral analysis and proper orthogonal decomposition (POD) to evaluate statistics of the velocity field and investigate the large-scale coherent motions of the wake. In all cases, we observe three distinct regions in the VAWT wake: (i) the near wake, where periodic blade vortex shedding dominates; (ii) a transition region, where growth of a shear-layer instability occurs; (iii) the far wake, where bluff-body wake oscillations dominate. We define a dynamic solidity parameter, \u03c3_D , that relates the characteristic scales of the flow to the streamwise transition location in the wake. In general, we find that increasing \u03c3_D leads to an earlier transition, a greater initial velocity deficit and a faster rate of recovery in the wake. We propose a coordinate transformation using \u03c3_D in which the minimum velocity recovery profiles of the VAWT wake closely match that of the cylinder wake. The results have implications for manipulating VAWT wake recovery within a wind farm.",
"doi": "10.1017/jfm.2016.862",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2017-02",
"volume": "813",
"pages": "346-381"
},
{
"id": "authors:bdn51-6zc33",
"collection": "authors",
"collection_id": "bdn51-6zc33",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102122",
"type": "conference_item",
"title": "Stability of wall-bounded flows using one-way spatial integration of Navier-Stokes equations",
"author": [
{
"family_name": "Rigas",
"given_name": "Georgios",
"orcid": "0000-0001-6692-6437",
"clpid": "Rigas-G"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Beyar",
"given_name": "Michael",
"clpid": "Beyar-Michael"
}
],
"abstract": "A method for constructing well-posed one-way equations for calculating disturbances of slowly-varying flows was recently introduced (Towne & Colonius, JCP, Vol. 300, 2015). The linearized Navier-Stokes equations are modified such that all upstream propagating modes are removed from the operator. The resulting equations, termed one-way Navier-Stokes equations, are stable and can be solved efficiently in the frequency domain as a spatial initial value problem in which initial perturbations are specified at the domain inlet and propagated downstream by spatial integration. To date, the method has been used to predict large-scale wavepacket structures and their acoustic radiation in turbulent jets. In this paper, the method is extended and applied to wall-bounded flows. Specifically, we examine the spatial stability of two- and three-dimensional boundary layers, corresponding to the Blasius and the Falkner-Skan-Cooke flows, and predict the evolution of unstable Tollmien-Schlichting waves and crossflow vortices, respectively. The method is validated against well-known results from the literature.",
"doi": "10.2514/6.2017-1881",
"publication_date": "2017-01-05"
},
{
"id": "authors:58rt9-3vt66",
"collection": "authors",
"collection_id": "58rt9-3vt66",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100791",
"type": "conference_item",
"title": "Wavepacket intermittency and its role in turbulent jet noise",
"author": [
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "The intermittent behavior of large-scale coherent structures in turbulent jets is studied. These structures are the primary source of jet noise, and their emitted sound is in turn characterized by rapid amplitude modulations of the pressure field. These high-energy bursts are well portrayed in the frequency-time domain by means of time-local analysis techniques. Scaleograms obtained from wavelet transforms of a single-point pressure signals, for example, enable the identification of such loud events at specific locations. Our interest, however, is in the time-local behavior of the coherent structures as a whole to gain a physical understanding of jet noise generation. For that purpose, a time series of large-eddy simulation snapshots is projected onto two sets of modal basis functions that describe the large-scale structures in the frequency-domain. The first modal basis consists of frequency-domain, or spectral, POD modes that are empirically deduced from the data. The second basis is comprised of resolvent response modes that are obtained from a linear frequency-response analysis of the mean flow. The proposed method allows us to visualize the intermittent behavior of the modal solutions in the frequency-time domain in terms of magnitude contours of the projection coefficient. The results can then be interpreted in an analogous way to wavelet scaleograms. The limitations, benefits and the potential of the method to yield a low-order representation of the flow in the time domain are discussed.",
"doi": "10.2514/6.2017-0686",
"publication_date": "2017-01-05"
},
{
"id": "authors:tt3ht-99f41",
"collection": "authors",
"collection_id": "tt3ht-99f41",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100696",
"type": "conference_item",
"title": "Modeling the Generation of Supersonic Turbulent Jet Noise by Large-Scale Coherent Structures",
"author": [
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "Large-scale coherent structures, or wavepackets, are a salient feature of turbulent jets, and the main source of jet mixing noise at aft angles. They are extracted from a high-fidelity Mach 1.5 LES database as spectral POD mode estimates. These most energetic wavepackets obtained via POD and their acoustic far-field radiation patterns are compared to solution to the one-way Euler (OWE) equations recently introduced by Towne & Colonius (AIAA Paper 2013-2171, 2013; AIAA Paper 2014-2903, 2014). Within the OWE framework, the linearized Euler equations are modified such that all upstream propagating acoustic wave components are removed from the solution. The resulting spatial initial value problem can be solved in a stable and computationally efficient manner by downstream marching the solution. Additionally, the scenario of stochastic forcing of wavepackets by the surrounding turbulence is considered in a resolvent analysis. The resolvent analysis allows for the computation of optimal forcing distributions and corresponding responses. It is based on a singular value decomposition of the transfer function of the governing linear operator. The results of the both methods, OWE and resolvent analysis, are compared to the most energetic POD modes with a special focus on far-field radiation patterns and computational efficiency.",
"doi": "10.1121/1.4969657",
"publication_date": "2016-11-18"
},
{
"id": "authors:wjt2h-tsw81",
"collection": "authors",
"collection_id": "wjt2h-tsw81",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102986",
"type": "conference_item",
"title": "Modeling and experimental analysis of acoustic cavitation bubble clouds for burst-wave lithotripsy",
"author": [
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Kreider",
"given_name": "Wayne",
"clpid": "Kreider-W"
},
{
"family_name": "Maxwell",
"given_name": "Adam",
"clpid": "Maxwell-A-D"
},
{
"family_name": "Bailey",
"given_name": "Michael",
"clpid": "Bailey-M-R"
}
],
"abstract": "Understanding the dynamics of cavitation bubble clouds formed inside a human body is critical for the design of burst-wave lithotripsy (BWL), a newly proposed method that uses focused ultrasound pulses with amplitude of O(10) MPa and frequency of O(0.1) MHz to fragment kidney stones. We present modeling and three-dimensional direct numerical simulations of interactions between bubble clouds and ultrasound pulses in water. We study two configurations: isolated clouds in a free field, and clouds near a rigid surface. In the modeling, we solve for the bubble radius evolution and continuous flow field using a WENO-based compressible flow solver. In the solver, Lagrangian bubbles are coupled with the continuous phase, defined on an Eulerian grid, at the sub-grid scale using volume averaging techniques. Correlations between the initial void fraction and the maximum collapse pressure in the cloud are discussed. We demonstrate acoustic imaging of the bubbles by post-processing simulated pressure signals at particular sensor locations indicating waves scattered by the clouds. Finally, we compare the simulation results with experimental results including high-speed imaging and hydrophone measurements. The time evolution of the cloud void fraction and the scattered acoustic field in the simulation agree with the experimental results.",
"doi": "10.1121/1.4970532",
"publication_date": "2016-11-18"
},
{
"id": "authors:th2xh-mbw54",
"collection": "authors",
"collection_id": "th2xh-mbw54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160714-085129783",
"type": "article",
"title": "Accurate computation of surface stresses and forces with immersed boundary methods",
"author": [
{
"family_name": "Goza",
"given_name": "Andres",
"orcid": "0000-0002-9372-7713",
"clpid": "Goza-A"
},
{
"family_name": "Liska",
"given_name": "Sebastian",
"orcid": "0000-0003-4139-9364",
"clpid": "Liska-S"
},
{
"family_name": "Morley",
"given_name": "Benjamin",
"clpid": "Morley-B"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Many immersed boundary methods solve for surface stresses that impose the velocity boundary conditions on an immersed body. These surface stresses may contain spurious oscillations that make them ill-suited for representing the physical surface stresses on the body. Moreover, these inaccurate stresses often lead to unphysical oscillations in the history of integrated surface forces such as the coefficient of lift. While the errors in the surface stresses and forces do not necessarily affect the convergence of the velocity field, it is desirable, especially in fluid\u2013structure interaction problems, to obtain smooth and convergent stress distributions on the surface. To this end, we show that the equation for the surface stresses is an integral equation of the first kind whose ill-posedness is the source of spurious oscillations in the stresses. We also demonstrate that for sufficiently smooth delta functions, the oscillations may be filtered out to obtain physically accurate surface stresses. The filtering is applied as a post-processing procedure, so that the convergence of the velocity field is unaffected. We demonstrate the efficacy of the method by computing stresses and forces that converge to the physical stresses and forces for several test problems.",
"doi": "10.1016/j.jcp.2016.06.014",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2016-09-15",
"volume": "321",
"pages": "860-873"
},
{
"id": "authors:3880g-c5e82",
"collection": "authors",
"collection_id": "3880g-c5e82",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161202-082406384",
"type": "book_section",
"title": "Leading Edge Vortex Development on Pitching and Surging Airfoils: A Study of Vertical Axis Wind Turbines",
"book_title": "Proceedings of the 5th International Conference on Jets, Wakes and Separated Flows (ICJWSF2015)",
"author": [
{
"family_name": "Dunne",
"given_name": "Reeve",
"clpid": "Dunne-R"
},
{
"family_name": "Tsai",
"given_name": "Hsieh-Chen",
"clpid": "Tsai-Hsieh-Chen"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "McKeon",
"given_name": "Beverley J.",
"orcid": "0000-0003-4220-1583",
"clpid": "McKeon-B-J"
}
],
"contributor": [
{
"family_name": "Segalini",
"given_name": "Antonio",
"clpid": "Segalini-A"
}
],
"abstract": "Vertical axis wind turbine blades undergo dynamic stall due to the large angle of attack variation they experience during a turbine rotation. Particle image velocimetry on a pitching and surging airfoil was used to perform time resolved measurements at blade Reynolds numbers near turbine operating conditions of 10^5. These experiments were compared to simulations performed in the rotating turbine frame as well as the linear, experimental, frame at a Reynolds number of 10^3 to investigate rotational and Reynolds number effects. The flow was shown to develop similarly prior to separation, but the kinematics of vortices shed post separation were reference frame dependent.",
"doi": "10.1007/978-3-319-30602-5_71",
"isbn": "978-3-319-30600-1",
"publisher": "Springer",
"place_of_publication": "Cham",
"publication_date": "2016-07-19",
"pages": "581-587"
},
{
"id": "authors:jqbj2-cwh81",
"collection": "authors",
"collection_id": "jqbj2-cwh81",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160523-085237573",
"type": "article",
"title": "A fast lattice Green's function method for solving viscous incompressible flows on unbounded domains",
"author": [
{
"family_name": "Liska",
"given_name": "Sebastian",
"orcid": "0000-0003-4139-9364",
"clpid": "Liska-S"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "A computationally efficient method for solving three-dimensional, viscous, incompressible flows on unbounded domains is presented. The method formally discretizes the incompressible Navier\u2013Stokes equations on an unbounded staggered Cartesian grid. Operations are limited to a finite computational domain through a lattice Green's function technique. This technique obtains solutions to inhomogeneous difference equations through the discrete convolution of source terms with the fundamental solutions of the discrete operators. The differential algebraic equations describing the temporal evolution of the discrete momentum equation and incompressibility constraint are numerically solved by combining an integrating factor technique for the viscous term and a half-explicit Runge\u2013Kutta scheme for the convective term. A projection method that exploits the mimetic and commutativity properties of the discrete operators is used to efficiently solve the system of equations that arises in each stage of the time integration scheme. Linear complexity, fast computation rates, and parallel scalability are achieved using recently developed fast multipole methods for difference equations. The accuracy and physical fidelity of solutions are verified through numerical simulations of vortex rings.",
"doi": "10.1016/j.jcp.2016.04.023",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2016-07-01",
"volume": "316",
"pages": "360-384"
},
{
"id": "authors:485bj-er132",
"collection": "authors",
"collection_id": "485bj-er132",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100223",
"type": "conference_item",
"title": "Numerical Investigation of Self-Starting Capability of Vertical-Axis Wind Turbines at Low Reynolds Numbers",
"author": [
{
"family_name": "Tsai",
"given_name": "Hsieh-Chen",
"clpid": "Tsai-Hsieh-Chen"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The self-starting capability of a NACA 0018 multi-bladed vertical-axis wind turbine is numerically investigated. The immersed boundary method is used to simulate the flow around a two-dimensional cross section of the wind turbine and the predictor-corrector method is used to couple the equation of motion of the turbine. A simple load model, which is linearly proportional to turbine angular velocity, is used for the load of the turbine. The angular velocity is characterized as a function of Reynolds number, density ratio, and viscous coefficient of the proposed load model. The power outputs and moment coefficients of motor-driven and flow-driven vertical-axis wind turbine are compared. For a particular Reynolds number, as the load on the flow-driven turbine is increased, the tip speed is reduced until the turbine fails to coherently rotate. The flow-driven and motor-driven moment coefficients in the computation have good agreement between each other and are qualitatively similar to the torque measured in experiments. These computations suggest that the load of a flow-driven turbine can be well-represented by the proposed load model and a motor-driven turbine can reproduce the physics of a flow-driven turbine within the range of tip-speed ratio examined. A simple model is proposed in order to analyze the starting torque. By assuming that the inertia of the blade is much larger than the fluid, the turbine can be considered stationary in the flow. The starting torque distribution of a multi-bladed turbine indicates the important orientations corresponding to maximum torque generation, at which a self-starting turbine always starts, and a stable equilibrium, where a non-self-starting turbine oscillates. These features agree with observations from the full simulations of the starting process. We further model the starting torque distribution by considering a single blade at different orientations, and construct starting torque distributions for multi-bladed turbines by linearly combining the torques at the respective positions of the blades. We show that this approximation is valid for a sufficiently low turbine solidity of about 0.5. Using this model, we find optimal starting configuration for a multi-bladed low-solidity vertical-axis wind turbine.",
"doi": "10.2514/6.2016-3731",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2016-06-10"
},
{
"id": "authors:e3rqf-bjg58",
"collection": "authors",
"collection_id": "e3rqf-bjg58",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059115",
"type": "conference_item",
"title": "Tonal dynamics and sound in subsonic turbulent jets",
"author": [
{
"family_name": "Jaunet",
"given_name": "Vincent",
"clpid": "Jaunet-V"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Schmidt",
"given_name": "Oliver",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "Acoustic waves trapped in the potential core of subsonic turbulent jets have recently been observed and explained by Towne et al. We show that these waves also radiate outside the jet, primarily into the upstream arc. We provide an experimental identification of the Mach-number dependence of the phenomenon, which indicates that the modes are active even when evanescent, probably due to turbulent forcing. Finally, we show that for Mach numbers lower than about 0.8, the strong tonal dynamics and sound radiation (up to 170dB) that occur when a sharp edge is placed close to the jet are related to a resonance mechanism involving convective hydrodynamic wavepackets and a 'slow', upstreampropagating, trapped acoustic mode. A Helmholtz scaling of the resonance at higher Mach number suggests involvement of the 'fast' trapped modes in the range 0.8 \u2264 M \u2264 1.",
"doi": "10.2514/6.2016-3016",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2016-05-27"
},
{
"id": "authors:206p7-tm064",
"collection": "authors",
"collection_id": "206p7-tm064",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112321549",
"type": "conference_item",
"title": "Large eddy simulation for jet noise: azimuthal decomposition and intermittency of the radiated sound",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Jaunet",
"given_name": "Vincent",
"clpid": "Jaunet-V"
},
{
"family_name": "Le Rallic",
"given_name": "Maxime",
"clpid": "Le-Rallic-M"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
}
],
"abstract": "To improve understanding and modeling of jet-noise source mechanisms, extensive experimental and numerical databases are generated for an isothermal Mach 0.9 turbulent jet at Reynolds number Re = 10^6. The large eddy simulations (LES) feature localized adaptive mesh refinement, synthetic turbulence and wall modeling inside the nozzle to match the fully turbulent nozzle-exit boundary layers in the experiments. Long LES databases are collected for two grids with different mesh resolutions in the jet plume. Comparisons with the experimental measurements show good agreement for the flow and sound predictions, with the far-field noise spectra matching microphone data to within 0.5 dB for most relevant angles and frequencies. Preliminary results on the radiated noise azimuthal decomposition and temporal intermittency are also discussed. The azimuthal analysis shows that the axisymmetric mode is dominant at the peak radiation angles and that the first 3 Fourier azimuthal modes of the LES data recover more than 97% of the total acoustic energy at these angles. The temporal analysis highlights the presence of recurring intermittency in the radiated sound for the low-frequency range and main downstream angles. At these frequencies and angles, temporally-localized bursts of noise can reach levels up to 3 or 4 dB higher (or lower) than the long-time average.",
"doi": "10.2514/6.2016-3050",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2016-05-27"
},
{
"id": "authors:jc7tm-gme66",
"collection": "authors",
"collection_id": "jc7tm-gme66",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100372",
"type": "conference_item",
"title": "Trapped acoustic waves in the potential core of subsonic jets",
"author": [
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Jaunet",
"given_name": "Vincent",
"clpid": "Jaunet-V"
},
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "The purpose of this paper is to characterize and model waves that are observed within the potential core of subsonic jets and that have been previously detected as tones in the near-nozzle region. Using three models (the linearized Euler equations, a cylindrical vortex sheet, and a cylindrical duct with pressure release boundary conditions), we show that these waves can be described by linear modes of the jet and correspond to acoustic waves that are trapped within the potential core. At certain frequencies, these trapped waves resonate due to repeated reflection between end conditions provided by the nozzle and the streamwise contraction of the potential core. Our models accurately capture numerous aspects the potential core waves that are extracted from large-eddy-simulation data of a Mach 0.9 isothermal jet. Furthermore, the vortex sheet model indicates that this behavior is possible for only a limited range of Mach numbers that is consistent with previous experimental observations.",
"doi": "10.2514/6.2016-2809",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2016-05-27"
},
{
"id": "authors:txt48-jgt85",
"collection": "authors",
"collection_id": "txt48-jgt85",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059776",
"type": "conference_item",
"title": "High-frequency wavepackets in turbulent jets",
"author": [
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Sasaki",
"given_name": "Kenzo",
"orcid": "0000-0002-3347-4996",
"clpid": "Sasaki-Kenzo"
},
{
"family_name": "Schmidt",
"given_name": "Oliver",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "Wavepackets obtained as solutions of the flow equations linearised around the mean flow have been shown in recent work to yield good agreement with the amplitudes and phases of turbulent fluctuations in jets. Compelling agreement has been demonstrated up to Strouhal numbers, St \u2248 1. We extend the range of validity of wavepacket models to higher values, 1.0 < St < 4.0, by comparing Parabolised Stability Equation solutions with well resolved large-eddy simulation data. The initial growth rates of the high-frequency fluctuations continue to be well predicted, but saturation occurs earlier and agreement with simulation begins to deteriorate upstream of the end of the potential core of the jet. Results show that near-nozzle dynamics for a broad range of frequencies can be modelled using linearised models, which capture well the spatial growth of Kelvin-Helmholtz wavepackets for all the studied Strouhal numbers.",
"doi": "10.2514/6.2016-3056",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2016-05-27"
},
{
"id": "authors:6fmnc-z4w16",
"collection": "authors",
"collection_id": "6fmnc-z4w16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100617",
"type": "conference_item",
"title": "Super- and multi-directive acoustic radiation by linear global modes of a turbulent jet",
"author": [
{
"family_name": "Schmidt",
"given_name": "Oliver T.",
"orcid": "0000-0002-7097-0235",
"clpid": "Schmidt-O-T"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Jaunet",
"given_name": "Vincent",
"clpid": "Jaunet-V"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "The mean flow stability of a Mach 0.9 turbulent jet is investigated by means of global linear theory with a focus on acoustic effects. A novel class of resonant acoustic modes that are trapped within the potential core, and whose eigenvalues appear as discrete branches in the global stability spectrum, is studied in detail. A dispersion relation is reconstructed from the global modes, and shown to accurately predict energy bands observed in the PSD of a high-fidelity LES. Similarly, the acoustic far-field radiation patterns of the trapped modes are compared to the LES. A favorable agreement between the global mode waveforms and coherent structures educed from the LES is found for both the trapped acoustic wave component inside the core and the far-field radiation.",
"doi": "10.2514/6.2016-2808",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2016-05-27"
},
{
"id": "authors:t4cn2-d7v25",
"collection": "authors",
"collection_id": "t4cn2-d7v25",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180713-132011622",
"type": "book_section",
"title": "Design and experimental evaluation of flextensional-cantilever based piezoelectric transducers for flow energy harvesting",
"book_title": "Smart Materials and Nondestructive Evaluation for Energy Systems 2016",
"author": [
{
"family_name": "Lee",
"given_name": "Hyeong Jae",
"clpid": "Lee-Hyeong-Jae"
},
{
"family_name": "Sherrit",
"given_name": "Stewart",
"orcid": "0000-0003-0656-4889",
"clpid": "Sherrit-Stewart"
},
{
"family_name": "Tosi",
"given_name": "Luis Phillipe",
"orcid": "0000-0002-0819-4765",
"clpid": "Tosi-L-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "Meyendorf",
"given_name": "Norbert G.",
"clpid": "Meyendorf-N-G"
},
{
"family_name": "Matikas",
"given_name": "Thomas E.",
"clpid": "Matikas-T-E"
},
{
"family_name": "Peters",
"given_name": "Kara J.",
"clpid": "Peters-K-J"
}
],
"abstract": "Cantilever type piezoelectric harvesters, such as bimorphs, are typically used for vibration induced energy harvesting. However, a major drawback of a piezoelectric bimorph is its brittle nature in harsh environments, precipitating short life-times as well as output power degradation. The emphasis in this work is to design robust, highly efficient piezoelectric harvesters that are capable of generating electrical power in the milliwatt range. Various harvesters were modeled, designed and prototyped, and the flextensional actuator based harvester, where the metal cantilever is mounted and coupled between two flextensional actuators, was found to be a viable alternative to the cantilever type piezoelectric harvesters. Preliminary tests show that these devices equipped with 5x5x36 mm two piezoelectric PZT stacks can produce greater than 50 mW of power under air flow induced vibrations.",
"doi": "10.1117/12.2219269",
"isbn": "9781510600478",
"publisher": "Society of Photo-optical Instrumentation Engineers (SPIE)",
"place_of_publication": "Bellingham, WA",
"publication_date": "2016-04-01",
"pages": "Art. No. 980610"
},
{
"id": "authors:7hbsa-t5v43",
"collection": "authors",
"collection_id": "7hbsa-t5v43",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160204-153835203",
"type": "article",
"title": "Parabolized stability analysis of jets from serrated nozzles",
"author": [
{
"family_name": "Sinha",
"given_name": "Aniruddha",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Gudmundsson",
"given_name": "Kristj\u00e1n",
"clpid": "Gudmundsson-K"
},
{
"family_name": "Xia",
"given_name": "Hao",
"clpid": "Xia-Hao"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We study the viscous spatial linear stability characteristics of the time-averaged flow in turbulent subsonic jets issuing from serrated (chevroned) nozzles, and compare them to analogous round jet results. Linear parabolized stability equations (PSE) are used in the calculations to account for the non-parallel base flow. By exploiting the symmetries of the mean flow due to the regular arrangement of serrations, we obtain a series of coupled two-dimensional PSE problems from the original three-dimensional problem. This reduces the solution cost and manifests the symmetries of the stability modes. In the parallel-flow linear stability theory (LST) calculations that are performed near the nozzle to initiate the PSE, we find that the serrated nozzle reduces the growth rates of the most unstable eigenmodes of the jet, but their phase speeds are approximately similar. We obtain encouraging validation of our linear PSE instability wave results vis-\u00e0-vis near-field hydrodynamic pressure data acquired on a phased microphone array in experiments, after filtering the latter with proper orthogonal decomposition (POD) to extract the energetically dominant coherent part. Additionally, a large-eddy simulation database of the same serrated jet is investigated, and its POD-filtered pressure field is found to compare favourably with the corresponding PSE solution within the jet plume. We conclude that the coherent hydrodynamic pressure fluctuations of jets from both round and serrated nozzles are reasonably consistent with the linear instability modes of the turbulent mean flow.",
"doi": "10.1017/jfm.2015.719",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2016-02",
"volume": "789",
"pages": "36-63"
},
{
"id": "authors:tk21n-wap73",
"collection": "authors",
"collection_id": "tk21n-wap73",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112320249",
"type": "conference_item",
"title": "Modeling Dynamic Lift Response to Actuation",
"author": [
{
"family_name": "An",
"given_name": "Xuanhong",
"clpid": "An-Xuanhong"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
},
{
"family_name": "Eldredge",
"given_name": "Jeff",
"clpid": "Eldredge-J-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The dynamic lift response of an airfoil to sinusoidal amplitude variations from a synthetic jet actuator was studied. The wing was at a fixed angle of attack, and the actuator operated in a 'burst-mode' with a fixed duty cycle. The actuator burst mplitude was used as a control signal, which was varied between an 'off ' condition and the actuator saturation voltage. Three dimensionless frequencies were examined, corresponding to k = [(\u03c0fc)/(U\u221e)] = 0.064, 0.128, and 0.25. Hysteresis loops in the lift increment were observed, whose shapes were dependent on the control frequency. Three different approaches to modeling the lift increment response were explored: a linear convolution approach, a nonlinear time delay and decay model, and a combination of those two. The linear convolution captures the high frequency content of the lift response, but becomes inaccurate when the actuator burst period is less than 3.5 convective times. The time delay and decay model reproduces the low frequency component of the lift response, but not the high frequency. When the control frequency becomes large, (k = 0.25), then the largest time-varying lift increment is produced near the minimum of the actuator voltage.",
"doi": "10.2514/6.2016-0058",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2016-01-02"
},
{
"id": "authors:zbn65-cqg97",
"collection": "authors",
"collection_id": "zbn65-cqg97",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059444",
"type": "conference_item",
"title": "A Vortex Sheet/Point Vortex Dynamical Model For Unsteady Separated Flows",
"author": [
{
"family_name": "Darakananda",
"given_name": "Darwin",
"clpid": "Darakananda-D"
},
{
"family_name": "Eldredge",
"given_name": "Jeff D.",
"clpid": "Eldredge-J-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
}
],
"abstract": "This paper presents a hybrid vortex sheet/point vortex method for modeling unsteady separated flows. We use vortex sheets to capture the dynamics of the shear layers immediately behind a wing in motion. The sheets provide a natural way of capturing vortex shedding, a feature missing from many point vortex models. We overcome the high computational cost traditionally associated with vortex sheet methods by approximating the spiraling cores of the sheets using point vortices with time-varying circulation. Circulation is continuously truncated from the tips of the vortex sheets and fed into their associated point vortices. To compensate for the discontinuous force response that results from this redistribution of vorticity, we adjust the velocity of the variable strength point vortices. We demonstrate the viability of the method by modeling the impulsive translation of a wing at a fixed angle of attack. We show that the proposed model correctly predicts the dynamics of large-scale vortical structures in the flow by comparing the distribution of vorticity from results of high-fidelity simulation, a model using only vortex sheets, and the proposed model. For the test cases attempted, the hybrid model predicts similar force responses to those of the sheet-only model, while being orders of magnitude faster.",
"doi": "10.2514/6.2016-2072",
"publisher": "American Institute of Aeronautics and Astronautics (AIAA)",
"publication_date": "2016-01-02"
},
{
"id": "authors:sz6a3-fza02",
"collection": "authors",
"collection_id": "sz6a3-fza02",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160303-101150959",
"type": "article",
"title": "Coriolis Effect on Dynamic Stall in a Vertical Axis Wind Turbine",
"author": [
{
"family_name": "Tsai",
"given_name": "Hsieh-Chen",
"clpid": "Tsai-Hsieh-Chen"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The immersed boundary method is used to simulate the flow around a two-dimensional cross section of a rotating NACA 0018 airfoil in order to investigate the dynamic stall occurring on a vertical axis wind turbine. The influence of dynamic stall on the force is characterized as a function of tip-speed ratio and Rossby number. The influence of the Coriolis effect is isolated by comparing the rotating airfoil to one undergoing an equivalent planar motion that is composed of surging and pitching motions that produce an equivalent speed and angle-of-attack variation over the cycle. Planar motions consisting of sinusoidally varying pitch and surge are also examined. At lower tip-speed ratios, the Coriolis force leads to the capture of a vortex pair when the angle of attack of a rotating airfoil begins to decrease in the upwind half cycle. This wake-capturing phenomenon leads to a significant decrease in lift during the downstroke phase. The appearance of this feature depends subtly on the tip-speed ratio. On the one hand, it is strengthened due to the intensifying Coriolis force, but on the other hand, it is attenuated because of the comitant decrease in angle of attack. While the present results are restricted to two-dimensional flow at low Reynolds numbers, they compare favorably with experimental observations at much higher Reynolds numbers. Moreover, the wake-capturing is observed only when the combination of surging, pitching, and Coriolis force is present.",
"doi": "10.2514/1.J054199",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2016-01",
"series_number": "1",
"volume": "54",
"issue": "1",
"pages": "216-226"
},
{
"id": "authors:7r1r1-80262",
"collection": "authors",
"collection_id": "7r1r1-80262",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160915-092423132",
"type": "book_section",
"title": "Parabolized Stability Analysis of Jets Issuing from Serrated Nozzles",
"book_title": "Fluid-Structure-Sound Interactions and Control",
"author": [
{
"family_name": "Sinha",
"given_name": "Aniruddha",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Xia",
"given_name": "Hao",
"clpid": "Xia-Hao"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "Zhou",
"given_name": "Yu",
"clpid": "Zhou-Yu"
},
{
"family_name": "Lucey",
"given_name": "A. D.",
"clpid": "Lucey-A-D"
},
{
"family_name": "Liu",
"given_name": "Yang",
"clpid": "Liu-Yang"
},
{
"family_name": "Huang",
"given_name": "Lixi",
"clpid": "Huang-Lixi"
}
],
"abstract": "Jets issuing from serrated nozzles have a correspondingly serrated time-averaged flow field. We solve the mildly non-parallel linear parabolized stability problem for such high speed turbulent jets to model the coherent wavepackets in the flow. The base flow for the analysis is the mean flow field from a large-eddy simulation database of a cold Mach 0.9 fully turbulent jet issuing from a nozzle with six serrations, a benchmark case in the literature. The fluctuation data is also filtered to extract the most-energetic coherent part using proper orthogonal decomposition. Such filtered data is shown to bear an encouraging resemblance with the predicted wavepackets.",
"doi": "10.1007/978-3-662-48868-3_34",
"isbn": "978-3-662-48866-9",
"publisher": "Springer",
"place_of_publication": "Heidelberg",
"publication_date": "2015-12-18",
"pages": "211-215"
},
{
"id": "authors:cctdc-7sk68",
"collection": "authors",
"collection_id": "cctdc-7sk68",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322726",
"type": "book_section",
"title": "Parbolized Stability Analysis of Jets Issuing from Serrated Nozzles",
"book_title": "Fluid-Structure-Sound Interactions and Control: Proceedings of the 3rd Symposium on Fluid-Structure-Sound Interactions and Control",
"author": [
{
"family_name": "Sinha",
"given_name": "Aniruddha",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Xia",
"given_name": "Hao",
"clpid": "Xia-Hao"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "Zhou",
"given_name": "Yu",
"clpid": "Zhou-Yu"
},
{
"family_name": "Lucey",
"given_name": "A. D.",
"clpid": "Lucey-A-D"
},
{
"family_name": "Liu",
"given_name": "Yang",
"clpid": "Liu-Yang"
},
{
"family_name": "Huang",
"given_name": "Lixi",
"clpid": "Huang-Lixi"
}
],
"abstract": "Jets issuing from serrated nozzles have a correspondingly serrated time-averaged flow field. We solve the mildly non-parallel linear parabolized stability problem for such high speed turbulent jets to model the coherent wavepackets in the flow. The base flow for the analysis is the mean flow field from a large-eddy simulation database of a cold Mach 0.9 fully turbulent jet issuing from a nozzle with six serrations, a benchmark case in the literature. The fluctuation data is also filtered to extract the most-energetic coherent part using proper orthogonal decomposition. Such filtered data is shown to bear an encouraging resemblance with the predicted wavepackets.",
"doi": "10.1007/978-3-662-48868-3_34",
"isbn": "9783662488669",
"publisher": "Springer",
"place_of_publication": "Berlin, Germany",
"publication_date": "2015-12-18",
"pages": "211-215"
},
{
"id": "authors:1d0vq-sb702",
"collection": "authors",
"collection_id": "1d0vq-sb702",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160211-085648396",
"type": "article",
"title": "Modeling and experimental analysis of acoustic cavitation bubbles for Burst Wave Lithotripsy",
"author": [
{
"family_name": "Maeda",
"given_name": "Kazuki",
"orcid": "0000-0002-5729-6194",
"clpid": "Maeda-Kazuki"
},
{
"family_name": "Kreider",
"given_name": "Wayne",
"clpid": "Kreider-Wayne"
},
{
"family_name": "Maxwell",
"given_name": "Adam",
"clpid": "Maxwell-Adam-D"
},
{
"family_name": "Cunitz",
"given_name": "Bryan",
"clpid": "Cunitz-Bryan"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Bailey",
"given_name": "Michael",
"clpid": "Bailey-Michael-R"
}
],
"abstract": "Cavitation bubbles initiated by focused ultrasound waves are investigated through experiments and modeling. Pulses of focused ultrasound with a frequency of 335 kHz and a peak negative pressure of 8 MPa is generated in a water tank by a piezoelectric transducer to initiate cavitation. The pressure field is modeled by solving the Euler equations and used to simulate single bubble oscillation. The characteristics of cavitation bubbles observed by highspeed photography qualitatively agree with the simulation results. Finally, bubble clouds are captured using acoustic B-mode imaging that works synchronized with high-speed photography.",
"doi": "10.1088/1742-6596/656/1/012027",
"pmcid": "PMC4831575",
"issn": "1742-6596",
"publisher": "IOP",
"publication": "Journal of Physics: Conference Series",
"publication_date": "2015-12-03",
"volume": "656",
"pages": "Art. No. 012027"
},
{
"id": "authors:2nkh7-j6r42",
"collection": "authors",
"collection_id": "2nkh7-j6r42",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151015-074155757",
"type": "article",
"title": "One-way spatial integration of hyperbolic equations",
"author": [
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "In this paper, we develop and demonstrate a method for constructing well-posed one-way approximations of linear hyperbolic systems. We use a semi-discrete approach that allows the method to be applied to a wider class of problems than existing methods based on analytical factorization of idealized dispersion relations. After establishing the existence of an exact one-way equation for systems whose coefficients do not vary along the axis of integration, efficient approximations of the one-way operator are constructed by generalizing techniques previously used to create nonreflecting boundary conditions. When physically justified, the method can be applied to systems with slowly varying coefficients in the direction of integration. To demonstrate the accuracy and computational efficiency of the approach, the method is applied to model problems in acoustics and fluid dynamics via the linearized Euler equations; in particular we consider the scattering of sound waves from a vortex and the evolution of hydrodynamic wavepackets in a spatially evolving jet. The latter problem shows the potential of the method to offer a systematic, convergent alternative to ad hoc regularizations such as the parabolized stability equations.",
"doi": "10.1016/j.jcp.2015.08.015",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2015-11-01",
"volume": "300",
"pages": "844-861"
},
{
"id": "authors:efkfh-atp20",
"collection": "authors",
"collection_id": "efkfh-atp20",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151027-114411683",
"type": "article",
"title": "Piezoelectric Energy Harvesting in Internal Fluid Flow",
"author": [
{
"family_name": "Lee",
"given_name": "Hyeong Jae",
"clpid": "Lee-Hyeong-Jae"
},
{
"family_name": "Sherrit",
"given_name": "Stewart",
"orcid": "0000-0003-0656-4889",
"clpid": "Sherrit-Stewart"
},
{
"family_name": "Tosi",
"given_name": "Luis Phillipe",
"orcid": "0000-0002-0819-4765",
"clpid": "Tosi-L-P"
},
{
"family_name": "Walkemeyer",
"given_name": "Phillip",
"clpid": "Walkemeyer-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We consider piezoelectric flow energy harvesting in an internal flow environment with the ultimate goal powering systems such as sensors in deep oil well applications. Fluid motion is coupled to structural vibration via a cantilever beam placed in a converging-diverging flow channel. Two designs were considered for the electromechanical coupling: first; the cantilever itself is a piezoelectric bimorph; second; the cantilever is mounted on a pair of flextensional actuators. We experimentally investigated varying the geometry of the flow passage and the flow rate. Experimental results revealed that the power generated from both designs was similar; producing as much as 20 mW at a flow rate of 20 L/min. The bimorph designs were prone to failure at the extremes of flow rates tested. Finite element analysis (FEA) showed fatigue failure was imminent due to stress concentrations near the bimorph's clamped region; and that robustness could be improved with a stepped-joint mounting design. A similar FEA model showed the flextensional-based harvester had a resonant frequency of around 375 Hz and an electromechanical coupling of 0.23 between the cantilever and flextensional actuators in a vacuum. These values; along with the power levels demonstrated; are significant steps toward building a system design that can eventually deliver power in the Watts range to devices down within a well.",
"doi": "10.3390/s151026039",
"issn": "1424-8220",
"publisher": "MDPI",
"publication": "Sensors",
"publication_date": "2015-10",
"series_number": "10",
"volume": "15",
"issue": "10",
"pages": "26039-26062"
},
{
"id": "authors:tkjgp-7m230",
"collection": "authors",
"collection_id": "tkjgp-7m230",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150814-110653004",
"type": "article",
"title": "Spatial Stability Analysis of Subsonic Jets Modified for Low-Frequency Noise Reduction",
"author": [
{
"family_name": "Uzun",
"given_name": "Ali",
"clpid": "Uzun-A"
},
{
"family_name": "Alvi",
"given_name": "Farrukh S.",
"clpid": "Alvi-F-S"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Hussaini",
"given_name": "M. Yousuff",
"clpid": "Hussaini-M-Y"
}
],
"abstract": "This study performs a spatial stability analysis of several jets that have previously been investigated in terms of their noise radiation. The cases include a round jet and two chevron nozzle jets with varying penetration angle. The instability wave evolution in the near-nozzle region is examined to seek for clues as to how and why the mean flow azimuthal inhomogeneity introduced by chevrons modifies the low-frequency noise component. A biglobal stability analysis is performed to determine the most unstable modes on an initial plane. The downstream evolution of the most unstable modes is then computed via three-dimensional parabolized stability equations. The azimuthal mean flow inhomogeneity introduced by chevrons is found to modify instability wave growth rates and phase speeds. Findings indicate that the near-field hydrodynamic pressure oscillations of round jet instability modes are suppressed by chevron jets. For the same modal excitation amplitude at the inlet, the two chevron jets generate considerably lower pressure fluctuations than the round jet. It is also shown that the chevron jet with the lowest hydrodynamic pressure fluctuation levels is the jet with the lowest far-field low-frequency noise output among the three jets.",
"doi": "10.2514/1.J053719",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2015-08",
"series_number": "8",
"volume": "53",
"issue": "8",
"pages": "2335-2358"
},
{
"id": "authors:vra8x-6vm60",
"collection": "authors",
"collection_id": "vra8x-6vm60",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150924-105657541",
"type": "article",
"title": "Optimal control of circular cylinder wakes using long control horizons",
"author": [
{
"family_name": "Flinois",
"given_name": "Thibault L. B.",
"clpid": "Flinois-T-L-B"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The classical problem of suppressing vortex shedding in the wake of a circular cylinder by using body rotation is revisited in an adjoint-based optimal control framework. The cylinder's unsteady and fully unconstrained rotation rate is optimized at Reynolds numbers between 75 and 200 and over horizons that are longer than in previous studies, where they are typically of the order of a vortex shedding period or shorter. In the best configuration, the drag is reduced by 19%, the vortex shedding is effectively suppressed, and this low drag state is maintained with minimal cylinder rotation after transients. Unlike open-loop control, the optimal control is shown to maintain a specific phase relationship between the actuation and the shedding in order to stabilize the wake. A comparison is also given between the performance of optimizations for different Reynolds numbers, cost functions, and horizon lengths. It is shown that the long horizons used are necessary in order to stabilize the vortex shedding efficiently.",
"doi": "10.1063/1.4928896",
"issn": "1070-6631",
"publisher": "American Institute of Physics",
"publication": "Physics of Fluids",
"publication_date": "2015-08",
"series_number": "8",
"volume": "27",
"issue": "8",
"pages": "Art. No. 087105"
},
{
"id": "authors:7md42-hnw11",
"collection": "authors",
"collection_id": "7md42-hnw11",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150702-123336452",
"type": "article",
"title": "Numerical simulations of the early stages of high-speed droplet breakup",
"author": [
{
"family_name": "Meng",
"given_name": "J. C.",
"orcid": "0000-0002-8966-2291",
"clpid": "Meng-Jomela-Chen-Chen"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Experiments reported in the literature are reproduced\nusing numerical simulations to investigate the early\nstages of the breakup of water cylinders in the flow behind\nnormal shocks. Qualitative features of breakup observed in\nthe numerical results, such as the initial streamwise flattening of the cylinder and the formation of tips at its periphery, support previous experimental observations of stripping breakup. Additionally, the presence of a transitory recirculation region at the cylinder's equator and a persistent upstream jet in the wake is noted and discussed. Within the uncertainties inherent to the different methods used to extract measurements from experimental and numerical results, comparisons with experimental data of various cylinder deformation metrics show good agreement. To study the effects of the transition between subsonic and supersonic post-shock flow, we extend the range of incident shock Mach numbers beyond those investigated by the experiments. Supersonic post-shock flow velocities are not observed to significantly alter the cylinder's behavior, i.e., we are able to effectively collapse the drift, acceleration, and drag curves for all simulated shock Mach numbers. Using a new method that minimizes noise errors, the cylinder's acceleration is calculated; acceleration curves for all shock Mach numbers are subsequently collapsed by scaling with the pressure ratio across the incident shock. Furthermore, we find that accounting for the cylinder's deformed diameter in the calculation of its unsteady drag coefficient allows the drag coefficient to be approximated as a constant over the initial breakup period.",
"doi": "10.1007/s00193-014-0546-z",
"issn": "0938-1287",
"publisher": "Springer",
"publication": "Shock Waves",
"publication_date": "2015-07",
"series_number": "4",
"volume": "25",
"issue": "4",
"pages": "399-414"
},
{
"id": "authors:8r1qg-kbh77",
"collection": "authors",
"collection_id": "8r1qg-kbh77",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322634",
"type": "conference_item",
"title": "Sensitivity of wavepackets in jets to non-linear effects: the role of the critical layer",
"author": [
{
"family_name": "Tissot",
"given_name": "Gilles",
"clpid": "Tissot-Gilles"
},
{
"family_name": "Zhang",
"given_name": "Mengqi",
"clpid": "Zhang-Mengqi"
},
{
"family_name": "Laj\u00fas",
"given_name": "Francisco C., Jr.",
"clpid": "Laj\u00fas-Francisco-C-Jr"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Linear instability waves, wavepackets, are key building blocks for the jet-noise problem. It has been shown in previous work that linear models correctly predict the evolution of axisymmetric wavepackets up to the end of the potential core. Beyond this station linear models fail to predict single-point statistics; they fail more broadly in the prediction of two-point properties such as coherence; and their underprediction of the radiated noise is believed to be associated with these errors. Non-linearity is the likely missing piece. But how might it be incorporated? What are the essential underlying mechanisms? Might it be amenable to a reduced-order modelling methodology? The work described in this paper is concerned with these questions. The non-linear interactions are considered as an \"external\" harmonic forcing of the standard linear model; the forcing can be viewed as comprising those Fourier components of the non-linear term of the Navier-Stokes equations which are most amplified by the linear wavepackets. \n\nThis modelling framework is explored using three complementary problems in which we try to understand the relationship between \"external\" forcing, linear system and flow response. The response of an incompressible, two-dimensional, locally parallel, shear-flow to direct, spatially localised, harmonic forcing is first considered. A resolvant analysis is then performed, again in a locally parallel context, both for the incompressible, 2D problem and for a compressible axisymmetric shear-flow where the mean flow is taken from experiments. Finally, in order to incorporate the slow axial variation of the real jet, a novel approach is considered where 4D-Var data assimilation is applied using experimental data and the Parabolised Stability Equations (PSE-4D-Var). The objective of this third, data-driven, approach is to search for an optimal forcing that might improve the match between wavepaket solutions and measurements. \n\nIn all of the problems considered the critical layer, where the phase speed of the wave is equal to the local mean velocity, is found to be relevant. It is at this point that the sensitivity of the linear waves to non-linearity is greatest. In the 2D, incompressible, problem the largest response is produced when the flow is forced in the vicinity of the critical layer. The resolvant analyses show optimal forcing modes that peak on the critical layer and the optimal response modes have a critical-layer structure. The PSE-4D-Var approach shows highest sensitivity near the critical layer. Furthermore, the structure of the forced perturbations are tilted in a manner that suggests an Orr-like mechanism.\n\nThe ensemble of results suggest that the critical layer may play a central role in the modelling of wavepackets in subsonic turbulent jets, and indeed may be the key to remedying the deficiencies evoked above.",
"doi": "10.2514/6.2015-2218",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2015-06-18"
},
{
"id": "authors:b5g4h-7dg30",
"collection": "authors",
"collection_id": "b5g4h-7dg30",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322014",
"type": "conference_item",
"title": "Large eddy simulation for jet noise: the importance of getting the boundary layer right",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Jaunet",
"given_name": "Vincent",
"clpid": "Jaunet-V"
},
{
"family_name": "Le Rallic",
"given_name": "Maxime",
"clpid": "Le-Rallic-M"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
}
],
"abstract": "Large eddy simulations of an isothermal Mach 0.9 jet issued from a convergent-straight nozzle are performed at Reynolds number 1 \u00d7 10^6. The flow configuration and operating conditions match the companion experiment conducted at the PPRIME Institute, Poitiers. To replicate the effects of the boundary layer trip present in the experiment and to ensure a turbulent jet, localized adaptive mesh refinement, synthetic turbulence, and wall modeling are used inside the nozzle. This leads to fully turbulent nozzle-exit boundary layers and results in significant improvements for the flow field and sound predictions, compared to those obtained from the typical approach based on laminar flow assumption in the nozzle. The far-field noise spectra now match the experimental measurements to within 0.5 dB for relevant angles and frequencies. As a next step toward better understanding of turbulent jet noise, the large database collected during the simulation is currently being used for reduced order modeling and wavepacket analysis.",
"doi": "10.2514/6.2015-2535",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2015-06-18"
},
{
"id": "authors:nc2tg-bc569",
"collection": "authors",
"collection_id": "nc2tg-bc569",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322227",
"type": "conference_item",
"title": "Stochastic and nonlinear forcing of wavepackets in a Mach 0.9 jet",
"author": [
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
}
],
"abstract": "Recent studies have shown that while linear wavepacket models accurately reproduce experimentally observed, low azimuthal-wavenumber pressure fluctuations in the near field of turbulent jets, they significantly under-predict the intensity of the acoustic radiation produced in the subsonic case. In a linear context, \"jittering\" of the wavepackets, which can arise due to both stochastic and nonlinear interactions that force the wavepackets, has been hypothesized as a mechanism by which the radiation efficiency of wavepackets is greatly increased. We use data from a carefully validated large-eddy-simulation of a Mach 0.9 turbulent jet to explore this hypothesis. We analyze the LES data in frequency space using windowed segments of a set of snapshots spanning two thousand acoustic time units. We apply the linearized Navier-Stokes operator to this data in order to compute the non-linear forcing field that occurred in the LES simulations, and propose several techniques for educing the relation between the forcing and the observed flow fields. In particular, we employ empirical techniques to identify high energy modes (via proper orthogonal decomposition) in both the flow and acoustic fields, as well as a set of empirical resolvent modes that maximize either the gain between the forcing and flow fields, or the gain between the forcing and acoustic fields. The high gain modes are similar to the high energy modes in both cases, suggesting that the forcing fields are nearly uncorrelated in each realization. Both flow and acoustic fields appear to be driven by largely incoherent forcing corresponding to turbulence in the region of strong shear and, in particular, close to the critical layer. With the caveat that we have thus far only analyzed the axisymmetric mode of the disturbance fields, the results suggest that accurate linear wavepacket models that capture both the coherent flow and acoustic fields can be constructed if appropriate parameterizations of the stochastic forcing can be found, i.e. such forcings will excite the high gain modes to produce the observed coherent structures in both the near and far field.",
"doi": "10.2514/6.2015-2217",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2015-06-18"
},
{
"id": "authors:0kwpw-jvy14",
"collection": "authors",
"collection_id": "0kwpw-jvy14",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322917",
"type": "conference_item",
"title": "Linear Stability Implications of Mean Flow Variations in Turbulent Jets Issuing from Serrated Nozzles",
"author": [
{
"family_name": "Sinha",
"given_name": "Aniruddha",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Nozzle serrations or chevrons are being deployed for reducing the noise from jet engines. The turbulent mean flow field of such jets takes on a serrated character, and the linear stability eigenspectrum for such serrated mean flows determines the evolution of the coherent wavepackets that are linked to the aft angle noise radiated. In particular, the lower the growth rate and phase speed of the instability, the lower is the expected noise radiation. Here we identify four parameters of the mean flow serrations \u2013 viz. number of lobes, their protrusion, their width relative of overall circumference, and the average thickness of the shear layer. These four parameters are systematically varied to synthesize a family of mean flow profiles. The corresponding stability analyses indicate the following trends. As expected from results for round jets, the average shear layer thickness has an inverse effect on both growth rate and phase speed. Deeper penetration and higher number of lobes reduce the growth rate of the relevant instability while mildly enhancing its phase speed. The relative width of the lobes do not appear to be a relevant parameter. These theoretical trends are supported by noise measurements in the parametric study on chevron nozzles performed at NASA.",
"doi": "10.2514/6.2015-3125",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2015-06-18"
},
{
"id": "authors:2rrzx-xp278",
"collection": "authors",
"collection_id": "2rrzx-xp278",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180713-131155883",
"type": "book_section",
"title": "Fluid flow nozzle energy harvesters",
"book_title": "Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2015",
"author": [
{
"family_name": "Sherrit",
"given_name": "Stewart",
"orcid": "0000-0003-0656-4889",
"clpid": "Sherrit-Stewart"
},
{
"family_name": "Lee",
"given_name": "Hyeong Jae",
"clpid": "Lee-Hyeong-Jae"
},
{
"family_name": "Walkemeyer",
"given_name": "Phillip",
"clpid": "Walkemeyer-P"
},
{
"family_name": "Winn",
"given_name": "Tyler",
"clpid": "Winn-Tyler"
},
{
"family_name": "Tosi",
"given_name": "Luis Phillipe",
"orcid": "0000-0002-0819-4765",
"clpid": "Tosi-L-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "Lynch",
"given_name": "Jerome P.",
"clpid": "Lynch-J-P"
},
{
"family_name": "Wang",
"given_name": "Kon-Well",
"clpid": "Wang-Kon-Well"
},
{
"family_name": "Sohn",
"given_name": "Hoon",
"clpid": "Sohn-Hoon"
}
],
"abstract": "Power generation schemes that could be used downhole in an oil well to produce about 1 Watt average power with long-life (decades) are actively being developed. A variety of proposed energy harvesting schemes could be used to extract energy from this environment but each of these has their own limitations that limit their practical use. Since vibrating piezoelectric structures are solid state and can be driven below their fatigue limit, harvesters based on these structures are capable of operating for very long lifetimes (decades); thereby, possibly overcoming a principle limitation of existing technology based on rotating turbo-machinery. An initial survey [1] identified that spline nozzle configurations can be used to excite a vibrating piezoelectric structure in such a way as to convert the abundant flow energy into useful amounts of electrical power. This paper presents current flow energy harvesting designs and experimental results of specific spline nozzle/ bimorph design configurations which have generated suitable power per nozzle at or above well production analogous flow rates. Theoretical models for non-dimensional analysis and constitutive electromechanical model are also presented in this paper to optimize the flow harvesting system.",
"doi": "10.1117/12.2084574",
"isbn": "9781628415384",
"publisher": "Society of Photo-optical Instrumentation Engineers (SPIE)",
"place_of_publication": "Bellingham, WA",
"publication_date": "2015-04-03",
"pages": "Art. No. 943507"
},
{
"id": "authors:xfnn3-wny16",
"collection": "authors",
"collection_id": "xfnn3-wny16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112321094",
"type": "book_section",
"title": "Simulation and Modeling of Turbulent Jet Noise",
"book_title": "Direct and Large-Eddy Simulation IX",
"author": [
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Sinha",
"given_name": "A.",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Rodriguez",
"given_name": "D.",
"clpid": "Rodriguez-D-M"
},
{
"family_name": "Towne",
"given_name": "A.",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Liu",
"given_name": "J.",
"clpid": "Liu-J"
},
{
"family_name": "Br\u00e8s",
"given_name": "G. A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Appel\u00f6",
"given_name": "D.",
"clpid": "Appel\u00f6-D"
},
{
"family_name": "Hagstrom",
"given_name": "T.",
"clpid": "Hagstrom-T"
}
],
"contributor": [
{
"family_name": "Fr\u00f6hlich",
"given_name": "Jochen",
"clpid": "Fr\u00f6hlich-J"
},
{
"family_name": "Kuerten",
"given_name": "Hans",
"clpid": "Kuerten-H"
},
{
"family_name": "Geurts",
"given_name": "Bernard J.",
"clpid": "Geurts-B-J"
},
{
"family_name": "Armenio",
"given_name": "Vincenzo",
"clpid": "Armenio-V"
}
],
"abstract": "Jet noise reduction remains an important long-range goal in commercial and military aviation. Compared with their early counterparts, modern, ultrahigh-bypass-ratio turbofans on commercial aircraft are very quiet, but ever more stringent noise regulations dictate further reductions. In addition, hearing loss by personnel and community noise issues are prompting the military to seek noise reduction on future tactical aircraft. Further increase in bypass ratio not being a practical option, military applications in particular call for nuanced approaches to noise reduction including mixing devices like chevrons or even active noise control approaches using unsteady air injection. In this paper, we briefly review some recent developments in theoretical, experimental and computational approaches to understanding the sound radiated by largescale, coherent structures in jet turbulence that might guide these noise reduction efforts.",
"doi": "10.1007/978-3-319-14448-1_38",
"isbn": "9783319144474",
"publisher": "Springer",
"place_of_publication": "Switzerland",
"publication_date": "2015-01-28",
"pages": "305-310"
},
{
"id": "authors:hbpzk-j9561",
"collection": "authors",
"collection_id": "hbpzk-j9561",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150217-092612513",
"type": "article",
"title": "A study of linear wavepacket models for subsonic turbulent jets using local eigenmode decomposition of PIV data",
"author": [
{
"family_name": "Rodr\u00edguez",
"given_name": "Daniel",
"clpid": "Rodr\u00edguez-D"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
}
],
"abstract": "Locally-parallel linear stability theory (LST) of jet velocity profiles is revisited to study the evolution of the wavepackets and the manner in which the parabolized stability equations (PSE) approach models them. An adjoint-based eigenmode decomposition technique is used to project cross-sectional velocity profiles measured using time-resolved particle image velocimetry (PIV) on the different families of eigenmodes present in the LST eigenspectrum. Attention is focused on the evolution of the Kelvin\u2013Helmholtz (K\u2013H) eigenmode and the projection of experimental fluctuations on it, since in subsonic jets the inflectional K\u2013H instability is the only possible mechanism for linear amplification of the large-scale fluctuations, and governs the wavepacket evolution. Comparisons of the fluctuations extracted by projection onto K\u2013H eigenmode with PSE solutions and PIV measurements are made. We show that the jet can be divided into three main regions, classified with respect to the LST eigenspectrum. Near the jet exit, there is significant amplification of the K\u2013H mode; the PSE solution is shown to comprise almost exclusively the K\u2013H mode, and the agreement with experiments shows that the evolution of this mode dominates the near-nozzle fluctuations. For downstream positions, the Kelvin\u2013Helmholtz mode becomes stable and eventually merges with other branches of the eigenspectrum. The comparison between PSE, experiment and the projection onto the K\u2013H mode for downstream positions suggests that the mechanism of saturation and decay of wavepackets is related to a combination of several marginally stable modes, which is reasonably well modeled by linear PSE, but cannot be obtained in the usual application of locally-parallel stability dealing exclusively with the K\u2013H mode. In addition, the projection of empirical data on the K\u2013H eigenmode at a near-nozzle cross-section is shown to be a well-founded method for the determination of the amplitudes of the linear wavepacket models.",
"doi": "10.1016/j.euromechflu.2014.03.004",
"issn": "0997-7546",
"publisher": "Elsevier",
"publication": "European Journal of Mechanics B/Fluids",
"publication_date": "2015-01",
"volume": "49",
"pages": "308-321"
},
{
"id": "authors:wb377-d7a14",
"collection": "authors",
"collection_id": "wb377-d7a14",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150420-134149863",
"type": "article",
"title": "Surging and plunging oscillations of an airfoil at low Reynolds number",
"author": [
{
"family_name": "Choi",
"given_name": "Jeesoon",
"clpid": "Choi-Jeesoon"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
}
],
"abstract": "We investigate the forces and unsteady flow structures associated with harmonic oscillations of an airfoil in the streamwise (surging) and transverse (plunging) directions in two-dimensional simulations at low Reynolds number. For the surging case, we show that there are specific frequencies where the wake instability synchronizes with the unsteady motion of the airfoil, leading to significant changes in the mean forces. Resonant behaviour of the time-averaged forces is observed near the vortex shedding frequency and its subharmonic; the behaviour is reminiscent of the dynamics of the generic nonlinear oscillator known as the Arnol'd tongue or the resonance horn. Below the wake instability frequency, there are two regimes where the fluctuating forces are amplified and attenuated, respectively. A detailed study of the flow structures associated with leading-edge vortex (LEV) growth and detachment are used to relate this behaviour with the LEV acting either in phase with the quasi-steady component of the forces for the amplification case, or out of phase for the attenuation case. Comparisons with wind tunnel measurements show that phenomenologically similar dynamics occur at higher Reynolds number. Finally, we show that qualitatively similar phenomena occur during both surging and plunging.",
"doi": "10.1017/jfm.2014.674",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2015-01",
"volume": "763",
"pages": "237-253"
},
{
"id": "authors:yvnbp-8g870",
"collection": "authors",
"collection_id": "yvnbp-8g870",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170622-065228163",
"type": "book_section",
"title": "The Effects of Shock Strength on Droplet Breakup",
"book_title": "29th International Symposium on Shock Waves",
"author": [
{
"family_name": "Meng",
"given_name": "Jomela C.",
"orcid": "0000-0002-8966-2291",
"clpid": "Meng-Jomela-Chen-Chen"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "Bonazza",
"given_name": "Ricardo",
"clpid": "Bonazza-R"
},
{
"family_name": "Devesh",
"given_name": "Ranjan",
"clpid": "Devesh-R"
}
],
"abstract": "The breakup of droplets occurs in the combustion of multiphase mixtures and the atomization of liquid jets. Most experiments studying droplet breakup have used the passage of a normal shock to provide a step change to uniform flow conditions.",
"doi": "10.1007/978-3-319-16838-8_120",
"isbn": "978-3-319-16837-1",
"publisher": "Springer",
"place_of_publication": "Cham, Switzerland",
"publication_date": "2015",
"pages": "1535-1540"
},
{
"id": "authors:j86f3-86381",
"collection": "authors",
"collection_id": "j86f3-86381",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141030-085927201",
"type": "article",
"title": "A parallel fast multipole method for elliptic difference equations",
"author": [
{
"family_name": "Liska",
"given_name": "Sebastian",
"orcid": "0000-0003-4139-9364",
"clpid": "Liska-S"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "A new fast multipole formulation for solving elliptic difference equations on unbounded domains and its parallel implementation are presented. These difference equations can arise directly in the description of physical systems, e.g. crystal structures, or indirectly through the discretization of PDEs. In the analog to solving continuous inhomogeneous differential equations using Green's functions, the proposed method uses the fundamental solution of the discrete operator on an infinite grid, or lattice Green's function. Fast solutions O(N)O(N) are achieved by using a kernel-independent interpolation-based fast multipole method. Unlike other fast multipole algorithms, our approach exploits the regularity of the underlying Cartesian grid and the efficiency of FFTs to reduce the computation time. Our parallel implementation allows communications and computations to be overlapped and requires minimal global synchronization. The accuracy, efficiency, and parallel performance of the method are demonstrated through numerical experiments on the discrete 3D Poisson equation.",
"doi": "10.1016/j.jcp.2014.07.048",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2014-12-01",
"volume": "278",
"pages": "76-91"
},
{
"id": "authors:hmn69-p2t05",
"collection": "authors",
"collection_id": "hmn69-p2t05",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150108-133817483",
"type": "article",
"title": "Effect of direct bubble-bubble interactions on linear-wave propagation in bubbly liquids",
"author": [
{
"family_name": "Fuster",
"given_name": "D.",
"clpid": "Fuster-D"
},
{
"family_name": "Conoir",
"given_name": "J. M.",
"clpid": "Conoir-J-M"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We study the influence of bubble-bubble interactions on the propagation of linear acoustic waves in bubbly liquids. Using the full model proposed by Fuster and Colonius J. Fluid Mech. 688, 253 ( 2011)], numerical simulations reveal that direct bubble-bubble interactions have an appreciable effect for frequencies above the natural resonance frequency of the average size bubble. Based on the new results, a modification of the classical wave propagation theory is proposed. The results obtained are in good agreement with previously reported experimental data where the classical linear theory systematically overpredicts the effective attenuation and phase velocity.",
"doi": "10.1103/PhysRevE.90.063010",
"issn": "1539-3755",
"publisher": "American Physical Society",
"publication": "Physical Review E",
"publication_date": "2014-12",
"series_number": "6",
"volume": "90",
"issue": "6",
"pages": "Art. No."
},
{
"id": "authors:fzs7a-c7b95",
"collection": "authors",
"collection_id": "fzs7a-c7b95",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112321008",
"type": "conference_item",
"title": "Modeling vascular injury due to shock-induced bubble collapse in lithotripsy",
"author": [
{
"family_name": "Coralic",
"given_name": "Vedran",
"clpid": "Coralic-V"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Shock-induced collapse (SIC) of preexisting bubbles is investigated as a potential mechanism for vascular injury in shockwave lithotripsy (SWL). Preexisting bubbles exist under normal physiological conditions and grow larger and more numerous with ongoing treatment. We compute the three-dimensional SIC of a bubble using the multi-component Euler equations, and determine the resulting three-dimensional finite-strain deformation field in the material surrounding the collapsing bubble. We propose a criterion for vessel rupture and estimate the minimum bubble size, across clinical SWL pressures, which could result in rupture of microvasculature. Post-processing of the results and comparison to viscoelastic models for spherical bubble dynamics demonstrate that our results are insensitive to a wide range of estimated viscoelastic tissue properties during the collapse phase. During the jetting phase, however, viscoelastic effects are non-negligible. The minimum bubble size required to rupture a vessel is then estimated by adapting a previous model for the jet's penetration depth as a function of tissue viscosity.",
"doi": "10.1121/1.4899946",
"publication_date": "2014-10-23"
},
{
"id": "authors:52fdt-nh656",
"collection": "authors",
"collection_id": "52fdt-nh656",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322554",
"type": "conference_item",
"title": "Efficient jet noise models using the one-way Euler equations",
"author": [
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Experimental and numerical investigations have correlated large-scale coherent structures in turbulent jets with acoustic radiation to downstream angles, where sound is most intense. These structures can be modeled as linear instability modes of the turbulent mean flow. The parabolized stability equations have been successfully used to estimate the near-field evolution of these modes, but are unable to properly capture the acoustic field. We have recently developed an efficient method for calculating these linear modes that properly captures the acoustic field. The linearized Euler equations are modified such that all upstream propagating acoustic modes are removed from the operator. The resulting equations, called one-way Euler equations, can be stably and efficiently solved in the frequency domain as a spatial initial value problem in which initial perturbations are specified at the flow inlet and propagated downstream by integrating the equations. We demonstrate the accuracy and efficiency of the method by using it to model sound generation and propagation in jets. The results are compared to accurate large-eddy-simulation data for both subsonic and supersonic jets.",
"doi": "10.1121/1.4899470",
"publication_date": "2014-10-23"
},
{
"id": "authors:nb9qk-zbh59",
"collection": "authors",
"collection_id": "nb9qk-zbh59",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112320906",
"type": "conference_item",
"title": "Active control of noise from hot, supersonic turbulent jets",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Schlinker",
"given_name": "Robert H.",
"clpid": "Schlinker-R-H"
},
{
"family_name": "Reba",
"given_name": "Ramons A.",
"clpid": "Reba-R-A"
},
{
"family_name": "Shannon",
"given_name": "Dan",
"clpid": "Shannon-D-W"
}
],
"abstract": "We report on an experimental and reduced-order modeling study aimed at reducing mixing noise in hot supersonic jets relevant to military aircraft. A spinning valve is used to modulate four injection nozzles near the main jet nozzle lip over a range of frequencies and mass flow rates. Diagnostics include near-, mid-, and far-field microphone arrays aimed at measuring the effect of actuation on the near-field turbulent wavepacket structures and their correlation with mixing noise. The actuators provide more than 4 dB noise reduction at peak frequencies in the aft arc, and up to 2 dB reduction in OASPL. Experiments are performed to contrast the performance of steady and unsteady blowing with different amplitudes. The results to date suggest that the noise reduction is primarily associated with attenuated wave packet activity associated with the rapidly thickened shear layers that occur with both steady and unsteady blowing. Mean flow surveys are also preformed and serve as inputs to reduced-order models for the wave packets based on parabolized stability equations. These models are in turn used to corroborate the experimental evidence suggesting mechanisms of noise suppression in the actuated flow.",
"doi": "10.1121/1.4899469",
"publication_date": "2014-10-14"
},
{
"id": "authors:z72vz-waz16",
"collection": "authors",
"collection_id": "z72vz-waz16",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140911-085308346",
"type": "article",
"title": "Finite-volume WENO scheme for viscous compressible multicomponent flows",
"author": [
{
"family_name": "Coralic",
"given_name": "Vedran",
"clpid": "Coralic-V"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We develop a shock- and interface-capturing numerical method that is suitable for the simulation of multicomponent flows governed by the compressible Navier\u2013Stokes equations. The numerical method is high-order accurate in smooth regions of the flow, discretely conserves the mass of each component, as well as the total momentum and energy, and is oscillation-free, i.e. it does not introduce spurious oscillations at the locations of shockwaves and/or material interfaces. The method is of Godunov-type and utilizes a fifth-order, finite-volume, weighted essentially non-oscillatory (WENO) scheme for the spatial reconstruction and a Harten\u2013Lax\u2013van Leer contact (HLLC) approximate Riemann solver to upwind the fluxes. A third-order total variation diminishing (TVD) Runge\u2013Kutta (RK) algorithm is employed to march the solution in time. The derivation is generalized to three dimensions and nonuniform Cartesian grids. A two-point, fourth-order, Gaussian quadrature rule is utilized to build the spatial averages of the reconstructed variables inside the cells, as well as at cell boundaries. The algorithm is therefore fourth-order accurate in space and third-order accurate in time in smooth regions of the flow. We corroborate the properties of our numerical method by considering several challenging one-, two- and three-dimensional test cases, the most complex of which is the asymmetric collapse of an air bubble submerged in a cylindrical water cavity that is embedded in 10% gelatin.",
"doi": "10.1016/j.jcp.2014.06.003",
"pmcid": "PMC4122134",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2014-10-01",
"volume": "274",
"pages": "95-121"
},
{
"id": "authors:jp325-m9k37",
"collection": "authors",
"collection_id": "jp325-m9k37",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112320455",
"type": "book_section",
"title": "Modeling intermittent wavepackets and their radiated sound in a turbulent jet",
"author": [
{
"family_name": "Jordan",
"given_name": "P.",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Br\u00e8s",
"given_name": "G. A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Zhang",
"given_name": "M.",
"clpid": "Zhang-M"
},
{
"family_name": "Towne",
"given_name": "A.",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Lele",
"given_name": "S. K.",
"clpid": "Lele-S-K"
}
],
"contributor": [
{
"family_name": "Moin",
"given_name": "Parviz",
"clpid": "Moin-Parviz"
},
{
"family_name": "Urzay",
"given_name": "Javier",
"clpid": "Urzay-J"
}
],
"abstract": "We use data from a new, carefully validated, Large Eddy Simulation (LES) to investigate and model subsonic, turbulent, jet noise. Motivated by the observation that sound-source dynamics are dominated by instability waves (wavepackets), we examine mechanisms by which their intermittency can amplify their noise radiation. Two scenarios, both involving wavepacket evolution on time-dependent base flows, are investigated. In the first, we consider that the main effect of the changing base flow consists in different wavepacket ensembles seeing different steady mean fields, and having, accordingly, different acoustic efficiencies. In the second, the details of the base-flow time dependence also play a role in wavepacket sound production. Both short-time-averaged and slowly varying base flows are extracted from the LES data and used in conjunction with linearized wavepacket models, namely, the Parabolized Stability Equations (PSE), the One-Way Euler Equations (OWE), and the Linearized Euler Equations (LEE). All results support the hypothesized mechanism: wavepackets on time-varying base flows produce sound radiation that is enhanced by as much as 20dB in comparison to their long-time-averaged counterparts, and ensembles of wavepackets based on short-time-averaged base flows display similar amplification. This is not, however, sufficient to explain the sound levels observed in the LES and experiments. Further work is therefore necessary to incorporate two additional factors in the linear models, body forcing by turbulence and realistic inflow forcing, both of which have been identified as potentially important in producing the observed radiation efficiency.",
"publisher": "Center for Turbulence Research",
"publication_date": "2014-07"
},
{
"id": "authors:cwazm-0rb41",
"collection": "authors",
"collection_id": "cwazm-0rb41",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112321468",
"type": "book_section",
"title": "Large eddy simulation of a Mach 0.9 turbulent jet",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "G. A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Jordan",
"given_name": "P.",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Le Rallic",
"given_name": "M.",
"clpid": "Le-Rallic-M"
},
{
"family_name": "Jaunet",
"given_name": "V.",
"clpid": "Jaunet-V"
},
{
"family_name": "Lele",
"given_name": "S. K.",
"clpid": "Lele-S-K"
}
],
"abstract": "Large eddy simulations of an isothermal Mach 0.9 jet (Re = 10^6) issued from a convergent-straight nozzle are performed using the compressible flow solver CharLES. The flow configuration and operating conditions match the companion experiment conducted at the PPRIME Institute, Poitiers. To replicate the effects of the boundary layer trip present in the experiment and to ensure a turbulent jet, localized adaptive mesh refinement, synthetic turbulence, and wall modeling are used inside the nozzle. This leads to fully turbulent nozzle-exit boundary layers and results in significant improvements for the flow field and sound predictions, compared to those obtained from the typical approach based on laminar flow assumption in the nozzle. The far-field noise spectra now match the experimental measurements to within 0.5 dB for relevant angles and frequencies. As a next step toward better understanding of turbulent jet noise, the large database collected during the simulation is currently being used for reduced order modeling and wavepacket analysis (Jordan et al. 2014).",
"publisher": "Center for Turbulence Research",
"publication_date": "2014-07"
},
{
"id": "authors:zgg2x-nbk43",
"collection": "authors",
"collection_id": "zgg2x-nbk43",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322314",
"type": "conference_item",
"title": "Coriolis Effect on Dynamic Stall in a Vertical Axis Wind Turbine at Moderate Reynolds Number",
"author": [
{
"family_name": "Tsai",
"given_name": "Hsieh-Chen",
"clpid": "Tsai-Hsieh-Chen"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The immersed boundary method is used to simulate the flow around a two-dimensional rotating NACA 0018 airfoil at sub-scale Reynolds number in order to investigate the separated flow occurring on a vertical-axis wind turbine. The influence of dynamic stall on the forces is characterized as a function of tip-speed ratio. The influence of the Coriolis effect is also investigated by comparing the rotating airfoil to one undergoing a equivalent planar motion, which is composed of surging and pitching motions that produce an equivalent speed and angle-of-attack variation over the cycle. When the angle of attack of a rotating airfoil starts to decrease in the upwind half cycle, the Coriolis force leads to a wake-capturing phenomenon of a vortex pair at low tip-speed ratio. This effects occurs at a slightly different phase in each cycle and leads to a significant decrease in the average lift during the downstroke phase. Moreover, the wake-capturing is only observed when the combination of surging, pitching, and Coriolis force are present. Finally, an actuator model is placed at an appropriate location on the suction side of the airfoil surface to control the wake-capturing phenomenon. Based on preliminary simulations, a momentum coefficient above 0.02 was able to increase the average lift by more than 70% over the upwind-half cycle.",
"doi": "10.2514/6.2014-3140",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2014-06-13"
},
{
"id": "authors:p0qx6-atn77",
"collection": "authors",
"collection_id": "p0qx6-atn77",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322396",
"type": "conference_item",
"title": "Continued development of the one-way Euler equations: application to jets",
"author": [
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "An efficient method for calculating linearized disturbances to shear flows that accurately captures their acoustic radiation was recently introduced (Towne & Colonius, AIAA Paper 2013-2171, 2013). The linearized Euler equations are modified such that all upstream propagating acoustic modes are removed from the operator. The resulting equations, called one-way Euler equations, can be stably and efficiently solved in the frequency domain as a spatial initial value problem in which initial perturbations are specified at the flow inlet and propagated downstream by integration of the equations. In this paper, we continue the development of this method with the aim of using it to model wavepackets and their acoustic radiation in turbulent jets. Before turning attention to jets, two dimensional mixing layer noise results computed using the one-way Euler equations are shown to be in excellent agreement with a direct solution of the full Euler equations. The one-way Euler operator is then shown to accurately represent all downstream modes that exist in supersonic and subsonic parallel jets, while properly eliminating the upstream acoustic modes. Finally, the method is applied to a turbulent Mach 0.5 jet mean flow obtained from experimental measurements. The near-field one-way Euler results are similar to those obtained using a previous spatial marching technique called the parabolized stability equations. However, the one-way Euler solutions also include the acoustic fields. With further development, the results suggest that the one-way Euler equation could be used to obtain improved accuracy over the parabolized stability equations as a low-order jet noise model.",
"doi": "10.2514/6.2014-2903",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2014-06-13"
},
{
"id": "authors:4cmzg-23s42",
"collection": "authors",
"collection_id": "4cmzg-23s42",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140515-110845791",
"type": "article",
"title": "Unsteady effects in dense, high speed, particle laden flows",
"author": [
{
"family_name": "Regele",
"given_name": "J. D.",
"clpid": "Regele-J-D"
},
{
"family_name": "Rabinovitch",
"given_name": "J.",
"orcid": "0000-0002-1914-7964",
"clpid": "Rabinovitch-J"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Blanquart",
"given_name": "G.",
"orcid": "0000-0002-5074-9728",
"clpid": "Blanquart-G"
}
],
"abstract": "Dense high speed non-compacted multiphase flows exist in variable phase turbines, explosions, and ejector nozzles, where the particle volume fraction is in the range 0.001<\u03b1_d<0.5. A canonical problem that can be used to study modeling issues related to these types of flows is a shock wave impacting a planar particle cloud. Thus far, prior work has modeled the flow using a 1-D volume-averaged point particle approach and developed momentum and energy coupling terms that reproduce accurately the trajectory of particles in the experiments. Although these early results are promising, it is appropriate to question whether all aspects of the experimental flow can be captured using a one-dimensional model that is traditionally only used for dilute flows. Thus the objective of this work is to set-up a two-dimensional configuration that captures qualitatively the multidimensional behavior of a real three-dimensional particle cloud, but can be used as an exact solution to compare with an equivalent volume-averaged model. The 2-D data is phase-averaged to reduce it to one dimension, and x\u2013t diagrams are used to characterize the flow behavior. These results show the importance of the Reynolds stress term inside the particle cloud and in its turbulent wake. A one-dimensional (1-D) model is developed for direct comparison with the 2-D simulation. While the 1-D model characterizes the overall steady-state flow behavior well, it fails to capture aspects of the unsteady behavior inside and behind the particle cloud because it neglects important unclosed terms.",
"doi": "10.1016/j.ijmultiphaseflow.2013.12.007",
"issn": "0301-9322",
"publisher": "Elsevier",
"publication": "International Journal of Multiphase Flow",
"publication_date": "2014-05",
"volume": "61",
"pages": "1-13"
},
{
"id": "authors:s7msa-vcs77",
"collection": "authors",
"collection_id": "s7msa-vcs77",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180713-132555490",
"type": "book_section",
"title": "Flow energy piezoelectric bimorph nozzle harvester",
"book_title": "Active and Passive Smart Structures and Integrated Systems 2014",
"author": [
{
"family_name": "Sherrit",
"given_name": "Stewart",
"orcid": "0000-0003-0656-4889",
"clpid": "Sherrit-Stewart"
},
{
"family_name": "Lee",
"given_name": "Hyeong Jae",
"clpid": "Lee-Hyeong-Jae"
},
{
"family_name": "Walkemeyer",
"given_name": "Phillip",
"clpid": "Walkemeyer-P"
},
{
"family_name": "Hasenoehrl",
"given_name": "Jennifer",
"clpid": "Hasenoehrl-J"
},
{
"family_name": "Hall",
"given_name": "Jeffrey L.",
"clpid": "Hall-J-L"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Tosi",
"given_name": "Luis Phillipe",
"orcid": "0000-0002-0819-4765",
"clpid": "Tosi-L-P"
},
{
"family_name": "Arrazola",
"given_name": "Alvaro",
"clpid": "Arrazola-A"
},
{
"family_name": "Kim",
"given_name": "Namhyo",
"clpid": "Kim-Namhyo"
},
{
"family_name": "Sun",
"given_name": "Kai",
"clpid": "Sun-Kai"
},
{
"family_name": "Corbett",
"given_name": "Gary",
"clpid": "Corbett-G"
}
],
"contributor": [
{
"family_name": "Liao",
"given_name": "Wei-Hsin",
"clpid": "Liao-Wei-Hsin"
}
],
"abstract": "There is a need for a long-life power generation scheme that could be used downhole in an oil well to produce 1 Watt average power. There are a variety of existing or proposed energy harvesting schemes that could be used in this environment but each of these has its own limitations. The vibrating piezoelectric structure is in principle capable of operating for very long lifetimes (decades) thereby possibly overcoming a principle limitation of existing technology based on rotating turbo-machinery. In order to determine the feasibility of using piezoelectrics to produce suitable flow energy harvesting, we surveyed experimentally a variety of nozzle configurations that could be used to excite a vibrating piezoelectric structure in such a way as to enable conversion of flow energy into useful amounts of electrical power. These included reed structures, spring mass-structures, drag and lift bluff bodies and a variety of nozzles with varying flow profiles. Although not an exhaustive survey we identified a spline nozzle/piezoelectric bimorph system that experimentally produced up to 3.4 mW per bimorph. This paper will discuss these results and present our initial analyses of the device using dimensional analysis and constitutive electromechanical modeling. The analysis suggests that an order-of-magnitude improvement in power generation from the current design is possible.",
"doi": "10.1117/12.2045191",
"isbn": "9780819499837",
"publisher": "Society of Photo-optical Instrumentation Engineers (SPIE)",
"place_of_publication": "Bellingham, WA",
"publication_date": "2014-04-01",
"pages": "Art. No. 90570D"
},
{
"id": "authors:9trks-81d64",
"collection": "authors",
"collection_id": "9trks-81d64",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140421-160135900",
"type": "article",
"title": "Wavepacket models for supersonic jet noise",
"author": [
{
"family_name": "Sinha",
"given_name": "Aniruddha",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Rodr\u00edguez",
"given_name": "Daniel",
"clpid": "Rodr\u00edguez-D"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Gudmundsson and Colonius (J. Fluid Mech., vol. 689, 2011, pp. 97\u2013128) have recently shown that the average evolution of low-frequency, low-azimuthal modal large-scale structures in the near field of subsonic jets are remarkably well predicted as linear instability waves of the turbulent mean flow using parabolized stability equations. In this work, we extend this modelling technique to an isothermal and a moderately heated Mach 1.5 jet for which the mean flow fields are obtained from a high-fidelity large-eddy simulation database. The latter affords a rigourous and extensive validation of the model, which had only been pursued earlier with more limited experimental data. A filter based on proper orthogonal decomposition is applied to the data to extract the most energetic coherent components. These components display a distinct wavepacket character, and agree fairly well with the parabolized stability equations model predictions in terms of near-field pressure and flow velocity. We next apply a Kirchhoff surface acoustic propagation technique to the near-field pressure model and obtain an encouraging match for far-field noise levels in the peak aft direction. The results suggest that linear wavepackets in the turbulence are responsible for the loudest portion of the supersonic jet acoustic field.",
"doi": "10.1017/jfm.2013.660",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2014-03",
"volume": "742",
"pages": "71-95"
},
{
"id": "authors:2fayj-7tq31",
"collection": "authors",
"collection_id": "2fayj-7tq31",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131202-084606542",
"type": "article",
"title": "Inlet conditions for wave packet models in turbulent jets based on eigenmode decomposition of large eddy simulation data",
"author": [
{
"family_name": "Rodr\u00edguez",
"given_name": "Daniel",
"clpid": "Rodr\u00edguez-D"
},
{
"family_name": "Sinha",
"given_name": "Aniruddha",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "This paper makes contributions towards reduced-order models of wave packets in supersonic, turbulent jets. Wave packets are large-scale turbulent structures that are correlated and advected over distances that are large compared to the integral scales of turbulence, i.e., many jet diameters at the lowest frequencies. They are thought to be responsible for the peak noise radiated at shallow angles to the jet axis. Linear wave packet models based on the Parabolized Stability Equations (PSE) have been shown in the past to be in excellent agreement with statistical structures educed from experimental pressure and velocity data in subsonic jets. Here, we extend these models to supersonic jets and validate them using a Large Eddy Simulation (LES) database for an isothermal and a moderately heated Mach 1.5 turbulent jets. For supersonic jets, inlet conditions for PSE models are ambiguous, as a parallel flow stability analysis shows several unstable modes at the inlet cross section. We develop a bi-orthogonal decomposition and project the LES data onto the relevant families of instability waves. These serve as inlet conditions, including the amplitude and shape functions, for PSE solutions which are then favorably compared to the near-field pressure fields educed from LES.",
"doi": "10.1063/1.4824479",
"issn": "1070-6631",
"publisher": "American Institute of Physics",
"publication": "Physics of Fluids",
"publication_date": "2013-10",
"series_number": "10",
"volume": "25",
"issue": "10",
"pages": "Art. No. 105107"
},
{
"id": "authors:amkhf-j8620",
"collection": "authors",
"collection_id": "amkhf-j8620",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130718-085055399",
"type": "article",
"title": "Generalized characteristic relaxation boundary conditions for unsteady compressible flow simulations",
"author": [
{
"family_name": "Pirozzoli",
"given_name": "Sergio",
"clpid": "Pirozzoli-S"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We develop numerical boundary conditions for the compressible Navier\u2013Stokes equations based on a generalized relaxation approach (GRCBC), which hinges on locally one-dimensional characteristic projection at the computational boundaries, supplemented with available information from the flow exterior. The basic idea is to estimate the amplitude of incoming characteristic waves through first-order one-sided finite-difference approximations which involve the value of the reference flow state at the first exterior (ghost) point. Unlike other characteristic-based relaxation methods, the present one requires minimal user-supplied input, including the reference flow state, which may be totally or partially known, and in general may vary both in space and time. Furthermore, it can be applied to any type of computational boundary, either inflow or outflow, either subsonic or supersonic. The method is theoretically predicted to convey reduced reflection of waves at computational boundaries compared to other ones, and to have better properties of frequency response to injected disturbances. Numerical tests confirm the improvement of the nonreflecting performance, and demonstrate high degree of flexibility, also for problems with non-trivial far-field boundary conditions (e.g. flows in rotating reference frames) and for the artificial stimulation of subsonic turbulent boundary layers.",
"doi": "10.1016/j.jcp.2013.04.021",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2013-09-01",
"volume": "248",
"pages": "109-126"
},
{
"id": "authors:66nhj-xgz84",
"collection": "authors",
"collection_id": "66nhj-xgz84",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131010-095128306",
"type": "article",
"title": "Wavepackets in the velocity field of turbulent jets",
"author": [
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Rodr\u00edguez",
"given_name": "Daniel",
"clpid": "Rodr\u00edguez-D"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Gervais",
"given_name": "Yves",
"clpid": "Gervais-Y"
}
],
"abstract": "We study the velocity fields of unforced, high Reynolds number, subsonic jets, issuing from round nozzles with turbulent boundary layers. The objective of the study is to educe wavepackets in such flows and to explore their relationship with the radiated sound. The velocity field is measured using a hot-wire anemometer and a stereoscopic, time-resolved PIV system. The field can be decomposed into frequency and azimuthal Fourier modes. The low-angle sound radiation is measured synchronously with a microphone ring array. Consistent with previous observations, the azimuthal wavenumber spectra of the velocity and acoustic pressure fields are distinct. The velocity spectrum of the initial mixing layer exhibits a peak at azimuthal wavenumbers ranging from 4 to 11, and the peak is found to scale with the local momentum thickness of the mixing layer. The acoustic pressure field is, on the other hand, predominantly axisymmetric, suggesting an increased relative acoustic efficiency of the axisymmetric mode of the velocity field, a characteristic that can be shown theoretically to be caused by the radial compactness of the sound source. This is confirmed by significant correlations, as high as 10 %, between the axisymmetric modes of the velocity and acoustic pressure fields, these values being significantly higher than those reported for two-point flow\u2013acoustic correlations in subsonic jets. The axisymmetric and first helical modes of the velocity field are then compared with solutions of linear parabolized stability equations (PSE) to ascertain if these modes correspond to linear wavepackets. For all but the lowest frequencies close agreement is obtained for the spatial amplification, up to the end of the potential core. The radial shapes of the linear PSE solutions also agree with the experimental results over the same region. The results suggests that, despite the broadband character of the turbulence, the evolution of Strouhal numbers 0.3 \u2264 St \u2264 0.9 and azimuthal modes 0 and 1 can be modelled as linear wavepackets, and these are associated with the sound radiated to low polar angles.",
"doi": "10.1017/jfm.2013.346",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2013-09",
"volume": "730",
"pages": "559-592"
},
{
"id": "authors:1t44b-keq14",
"collection": "authors",
"collection_id": "1t44b-keq14",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130917-093943668",
"type": "article",
"title": "On a transitional and turbulent natural convection in spherical shells",
"author": [
{
"family_name": "Feldman",
"given_name": "Yuri",
"clpid": "Feldman-Y"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Laminar and turbulent natural convection inside concentric spherical shells with isothermal cold and hot boundaries is numerically investigated up to Rayleigh number values Ra \u2a7d 10^(12) and Pr = 0.71. The study utilizes direct numerical simulation (DNS), large eddy simulation (LES) and Reynolds averaged Navier\u2013Stokes (RANS) approaches for investigation of the laminar, transitional and fully developed turbulent flow regimes, respectively. Three-dimensional flow patterns for slightly supercritical oscillatory flow regime inside the shell, with internal/external diameter ratio equal to D_i/D_o = 0.714 are presented and may be potentially useful for verification of the future linear stability analysis results. Particular attention has been given to the complex, fully three-dimensional unsteady flows occurring in narrow shell geometries characterized by 0.85 \u2a7d D_i/D_o \u2a7d 0.95. For this geometry considerable deviations in predicted heat flux rate through the shell boundaries are observed when compared with existing heat transfer correlations for the entire range of Ra numbers. The deviations tend to increase for transitional and fully turbulent flows. A new correlation for the heat transfer rate is suggested for laminar and transitional flow regimes.",
"doi": "10.1016/j.ijheatmasstransfer.2013.04.042",
"issn": "0017-9310",
"publisher": "Elsevier",
"publication": "International Journal of Heat and Mass Transfer",
"publication_date": "2013-09",
"volume": "64",
"pages": "514-525"
},
{
"id": "authors:ttese-95c96",
"collection": "authors",
"collection_id": "ttese-95c96",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130605-141321734",
"type": "article",
"title": "Shock-induced collapse of a bubble inside a deformable vessel",
"author": [
{
"family_name": "Coralic",
"given_name": "Vedran",
"clpid": "Coralic-V"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Shockwave lithotripsy repeatedly focuses shockwaves on kidney stones to induce their fracture, partially\nthrough cavitation erosion. A typical side effect of the procedure is hemorrhage, which is potentially\nthe result of the growth and collapse of bubbles inside blood vessels. To identify the mechanisms by\nwhich shock-induced collapse could lead to the onset of injury, we study an idealized problem involving\na preexisting bubble in a deformable vessel. We utilize a high-order accurate, shock- and interfacecapturing,\nfinite-volume scheme and simulate the three-dimensional shock-induced collapse of an air\nbubble immersed in a cylindrical water column which is embedded in a gelatin/water mixture. The\nmixture is a soft tissue simulant, 10% gelatin by weight, and is modeled by the stiffened gas equation\nof state. The bubble dynamics of this model configuration are characterized by the collapse of the bubble\nand its subsequent jetting in the direction of the propagation of the shockwave. The vessel wall, which is\ndefined by the material interface between the water and gelatin/water mixture, is invaginated by the\ncollapse and distended by the impact of the jet. The present results show that the highest measured\npressures and deformations occur when the volumetric confinement of the bubble is strongest, the bubble\nis nearest the vessel wall and/or the angle of incidence of the shockwave reduces the distance between\nthe jet tip and the nearest vessel surface. For a particular case considered, the 40 MPa shockwave utilized\nin this study to collapse the bubble generated a vessel wall pressure of almost 450 MPa and produced both\nan invagination and distention of nearly 50% of the initial vessel radius on a O(10) ns timescale. These\nresults are indicative of the significant potential of shock-induced collapse to contribute to the injury of\nblood vessels in shockwave lithotripsy.",
"doi": "10.1016/j.euromechflu.2013.01.003",
"pmcid": "PMC3763519",
"issn": "0997-7546",
"publisher": "Elsevier",
"publication": "European Journal of Mechanics B/Fluids",
"publication_date": "2013-07",
"volume": "40",
"pages": "64-74"
},
{
"id": "authors:51jj6-hc925",
"collection": "authors",
"collection_id": "51jj6-hc925",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130716-141834071",
"type": "article",
"title": "Second-mode attenuation and cancellation by porous coatings in a high-speed boundary layer",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Inkman",
"given_name": "Matthew",
"clpid": "Inkman-M"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Fedorov",
"given_name": "Alexander V.",
"clpid": "Fedorov-A-V"
}
],
"abstract": "Numerical simulations of the linear and nonlinear two-dimensional Navier\u2013Stokes equations, and linear stability theory are used to parametrically investigate hypersonic boundary layers over ultrasonic absorptive coatings. The porous coatings consist of a uniform array of rectangular pores (slots) with a range of porosities and pore aspect ratios. For the numerical simulations, temporally (rather than spatially) evolving boundary layers are considered and we provide evidence that this approximation is appropriate for slowly growing second-mode instabilities. We consider coatings operating in the typical regime where the pores are relatively deep and acoustic waves and second-mode instabilities are attenuated by viscous effects inside the pores, as well as regimes with phase cancellation or reinforcement associated with reflection of acoustic waves from the bottom of the pores. These conditions are defined as attenuative and cancellation/reinforcement regimes, respectively. The focus of the present study is on the cases which have not been systematically studied in the past, namely the reinforcement regime (which represents a worst-case scenario, i.e. minimal second-mode damping) and the cancellation regime (which corresponds to the configuration with the most potential improvement). For all but one of the cases considered, the linear simulations show good agreement with the results of linear instability theory that employs an approximate porous-wall boundary condition, and confirm that the porous coating stabilizing performance is directly related to their acoustic scattering performance. A particular case with relatively shallow pores and very high porosity showed the existence of a shorter-wavelength instability that was not initially predicted by theory. Our analysis shows that this new mode is associated with acoustic resonances in the pores and can be more unstable than the second mode. Modifications to the theoretical model are suggested to account for the new mode and to provide estimates of the porous coating parameters that avoid this detrimental instability. Finally, nonlinear simulations confirm the conclusions of the linear analysis; in particular, we did not observe any tripping of the boundary layer by small-scale disturbances associated with individual pores.",
"doi": "10.1017/jfm.2013.206",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2013-07",
"volume": "726",
"pages": "312-337"
},
{
"id": "authors:143xf-j0g84",
"collection": "authors",
"collection_id": "143xf-j0g84",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20160526-114025207",
"type": "conference_item",
"title": "Droplet Breakup in High-Speed Gas Flows",
"author": [
{
"family_name": "Meng",
"given_name": "Jomela C.",
"orcid": "0000-0002-8966-2291",
"clpid": "Meng-Jomela-Chen-Chen"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Numerical simulations are performed to study the breakup of water cylinders in the flow behind normal shocks. The computational setup is similar to previous experiments (Igra and Takayama, 2001, 2003). We examine the qualitative features of the so-called stripping breakup observed in the numerical results. Two interesting flow features are discussed: the existence of recirculation regions and an upstream jet in the wake. Various integral quantities associated with the cylinder's deformation and acceleration are computed and compared with the experimental results, with generally good agreement. Furthermore, calculations of the velocity and acceleration of the cylinder's center of mass provide an estimate of the unsteady drag coefficient which is approximately constant over the initial breakup period.",
"publisher": "Caltech Library",
"publication_date": "2013-05-26"
},
{
"id": "authors:a6nxm-dhj24",
"collection": "authors",
"collection_id": "a6nxm-dhj24",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112323422",
"type": "conference_item",
"title": "Wavepacket eduction in turbulent jets based on eigenmode decomposition of PIV data",
"author": [
{
"family_name": "Rodr\u00edguez",
"given_name": "Daniel",
"clpid": "Rodr\u00edguez-D"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
}
],
"abstract": "The dynamics of large scale structures in unforced turbulent jets at subsonic speeds have been related to the generation of the peak noise radiated the aft direction. The utility of instability wavepackets computed by linear stability theory or parabolised stability equations (PSE) have been demonstrated for the modeling of the near-field pressure fluctuations associated with the coherent structures. In this paper, we investigate whether the velocity field corresponding to the wavepackets also represents adequately that of the coherent structures. Previous research showed remarkable agreement in the velocity field up to the end of the potential core, but the agreement is lost gradually downstream.\n\nLocally-parallel linear stability theory (LST) of jet velocity profiles is revisited to further study the evolution of the wavepackets and the manner in which PSE models them. An adjoint-based eigenmode decomposition technique is used to project cross-sectional velocity profiles measured using time-resolved particle image velocimetry (PIV) on the Kelvin-Helmholtz eigenmode responsible for the wavepacket amplification. The instability wave thus extracted is then compared, both in amplification and shape, to the PSE wavepacket and to the dominant coherent structures obtained from the proper orthogonal decomposition of the PIV measurements. The comparisons between PSE models and POD-filtered fluctuations define three spatial regions along the streamwise direction that are explained in terms of changes in the LST eigenspectrum.",
"doi": "10.2514/6.2013-2084",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2013-05-24"
},
{
"id": "authors:r38hz-1fy26",
"collection": "authors",
"collection_id": "r38hz-1fy26",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322809",
"type": "conference_item",
"title": "Toward Active Control of Noise from Hot Supersonic Jets",
"author": [
{
"family_name": "Sinha",
"given_name": "A.",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Schlinker",
"given_name": "R. H.",
"clpid": "Schlinker-R-H"
},
{
"family_name": "Simonich",
"given_name": "J. S.",
"clpid": "Simonich-J-S"
},
{
"family_name": "Reba",
"given_name": "R. A.",
"clpid": "Reba-R-A"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We present diagnostic experiments and reduced-order models aimed at understanding and mitigating supersonic jet noise from coherent wavepackets in the turbulent shear layer, generally accepted to be the source of peak aft-angle mixing noise. The work builds on a successful Caltech/UTRC modeling approach that predicts the evolution of the wavepackets as instability waves of the turbulent mean flow, as well as the noise radiated from their near field. The models are experimentally assessed for unforced and forced supersonic isothermal and heated Mach 1.5 jets from ideal expansion nozzles. A spinning valve device is used to inject air near the nozzle lip at frequencies up to a Strouhal number of about 0.25. Results indicate a 2-3 dB benefit near peak frequencies of the spectrum and a 2 dB OASPL reduction at a mass flow percentage of 3.2. For the same injection plenum pressure, steady blowing yields more noise benefit than the unsteady actuation schemes explored until now. However, this may be explained by the slight decrease in injection velocity incurred in going from steady to unsteady operation. The reduced-order models, based on parabolized stability equations (PSE), are found to be in good agreement, in terms of envelope and phase, with those educed from the experimental data of the unforced jet. For the actuation schemes we have considered to date, the model and experimental data support a tentative explanation for the observed noise reduction in terms of attenuation of the wavepacket amplitudes by the thickened shear layer. Wavepackets induced by the harmonic component of the actuation are linearly superposed on those produced by broadband turbulence, without significant interaction, such that they lead to the addition of tones to the far-field noise that are counterproductive as far as noise reduction is concerned.",
"doi": "10.2514/6.2013-2234",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2013-05-24"
},
{
"id": "authors:2mnxf-1rc73",
"collection": "authors",
"collection_id": "2mnxf-1rc73",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322471",
"type": "conference_item",
"title": "Improved Parabolization of the Euler Equations",
"author": [
{
"family_name": "Towne",
"given_name": "Aaron",
"orcid": "0000-0002-7315-5375",
"clpid": "Towne-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We present a new method for stability and modal analysis of shear flows and their acoustic radiation. The Euler equations are modified and solved as a spatial initial value problem in which initial perturbations are specified at the flow inlet and propagated downstream by integration of the equations. The modified equations, which we call one-way Euler equations, differ from the usual Euler equations in that they do not support upstream acoustic waves. It is necessary to remove these modes from the Euler operator because, if retained, they cause instability in the spatial marching procedure. These modes are removed using a two-step process. First, the upstream modes are partially decoupled from the downstream modes using a linear similarity transformation. Second, the error in the first step is eliminated using a convergent recursive filtering technique. A previous spatial marching method called the parabolized stability equations uses numerical damping to stabilize the march, but this has the unintended consequence of heavily damping the downstream acoustic waves. Therefore, the one-way Euler equation could be used to obtain improved accuracy over the parabolized stability equations as a low-order model for noise simulation of mixing layers and jets.",
"doi": "10.2514/6.2013-2171",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2013-05-24"
},
{
"id": "authors:0xxzs-2by21",
"collection": "authors",
"collection_id": "0xxzs-2by21",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322147",
"type": "conference_item",
"title": "Near-field wavepackets and the far-field sound of a subsonic jet",
"author": [
{
"family_name": "Breakey",
"given_name": "David E. S.",
"clpid": "Breakey-D-E-S"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Olivier",
"given_name": "L\u00e9on",
"clpid": "Olivier-L\u00e9on"
},
{
"family_name": "Zhang",
"given_name": "Mengqi",
"clpid": "Zhang-Mengqi"
},
{
"family_name": "Lehnasch",
"given_name": "Guillaume",
"clpid": "Lehnasch-Guillaume"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Rodr\u00edguez",
"given_name": "Daniel",
"clpid": "Rodr\u00edguez-D"
}
],
"abstract": "This paper details the analysis of the relationship between the near-field pressure fluctuations of an unforced, subsonic free jet (0.4 \u2264 M \u2264 0.6) and its low-angle, far-field sound emissions. Azimuthal rings of six microphones recorded pressure fluctuations on a conical surface in the jet near field while an azimuthal ring of three microphones recorded fluctuations in the far field at \u03b8 = 20\u00b0 and R/D = 47.1. Recent measurements have shown close agreement between the velocity fluctuations up to the end of the potential core of the currently studied jet and predictions from the linear Parabolised Stability Equations (PSE), indicating the presence of linear wavepackets in the jet velocity field. Solutions of the Linearised Euler Equations (LEE) reported in the present paper also show good agreement with measurements, and provide a first step toward a time-domain description of the said wavepackets. Though the agreement for PSE in the velocity field breaks down downstream of the potential core, Proper Orthogonal Decomposition (POD) of the current results shows that the wavepackets do persist in this region and are clearly apparent in the near pressure field. Attention is then turned to establishing a relationship between these wavepackets and the radiated sound by comparing simultaneously-obtained measurements of the far-field pressure both directly to the near-field signature as well as to numerical predictions of the far-field emissions available from a recent technique using a tailored Green's function. The direct comparisons are made by correlations between the POD modes and the far-field sound. The first POD mode captures most of the flow energy for the frequency range studied, and the correlation between this mode and the far field is nearly identical to the correlation using the full near-field signal. Higher POD modes also show significant correlation to the far field with a different space\u2013time structure than the first mode. The Green's function predictions are performed both statistically and in the time domain, and though they are shown to be valid for a near-field array with a long axial extent, the experimental limitation of a shorter array (0.5 \u2264 x/D \u2264 8.9), which truncates the wavepacket source in the calculations, causes inaccurate predictions for the experimental data. This error is thought to be the result of a spurious source introduced by the truncation that interferes both constructively and destructively with the wavepacket source. A validation problem shows that this error would be smaller for a higher-M jet.",
"doi": "10.2514/6.2013-2083",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2013-05-24"
},
{
"id": "authors:nmmsp-d9g46",
"collection": "authors",
"collection_id": "nmmsp-d9g46",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112323164",
"type": "conference_item",
"title": "Acoustic field associated with parabolized stability equation models in turbulent jets",
"author": [
{
"family_name": "Rodr\u00edguez",
"given_name": "Daniel",
"clpid": "Rodr\u00edguez-D"
},
{
"family_name": "Sinha",
"given_name": "Aniruddha",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Wavepackets are large-scale turbulent structures that are correlated and advected over distances that are large compared to the integral scales of turbulence, and have been shown to be responsible for the peak noise radiated at aft angles to the jet axis. The present paper discusses linear models of these wavepackets for supersonic turbulent jets based on Parabolized Stability Equations (PSE). In the past, results of this approach were shown to be in excellent agreement with coherent structures extracted from experimental near-field pressure and velocity data in subsonic jets. Here, we make use of a Large Eddy Simulation (LES) database for an isothermal and a moderately heated Mach 1.5 turbulent jets. Careful comparisons of the PSE models with near-field pressure fields from LES, filtered by means of Proper Orthogonal Decomposition (POD), demonstrate acceptable fidelity of the model. Finally, the acoustic far-field associated with the PSE wavepackets is computed using a Kirchhoff surface method, capturing reasonably well the far-field pressure at angles close to the peak.",
"doi": "10.2514/6.2013-2279",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2013-05-23"
},
{
"id": "authors:d9vec-4a623",
"collection": "authors",
"collection_id": "d9vec-4a623",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112321331",
"type": "conference_item",
"title": "Dynamics and Energy Extraction of a Surging and Plunging Airfoil at Low Reynolds Number",
"author": [
{
"family_name": "Choi",
"given_name": "Jeesoon",
"clpid": "Choi-Jeesoon"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Williams",
"given_name": "David",
"clpid": "Williams-D"
}
],
"abstract": "We investigate the unsteady aerodynamic forces and energy transfer associated with harmonic surging (streamwise) and plunging (transverse) motion of a thin airfoil at low Reynolds number. Two-dimensional unsteady flows are simulated over a large range of amplitude and reduced-frequency of the oscillatory motion using the immersed boundary projection method, and the computational results are compared to inviscid flow models and experiments. At low angle of attack there is reasonable agreement with inviscid theory for the amplitude and phase of lift fluctuations, despite the low Reynolds number. At high angle of attack, the separated flow leads to larger lift and drag fluctuations not captured by inviscid models. At frequencies below the vortex shedding frequency, lift fluctuations are first enhanced and then attenuated depending on the phase between the freestream velocity and the forming leading-edge vortex. Resonance with the vortex shedding frequency also occurs. The time-averaged forces and power supplied by the oscillating airfoil are also evaluated to find frequency ranges that are favorable for the airfoil.",
"doi": "10.2514/6.2013-672",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2013-01-05"
},
{
"id": "authors:grnfr-k1q39",
"collection": "authors",
"collection_id": "grnfr-k1q39",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130506-104903569",
"type": "article",
"title": "Wave Packets and Turbulent Jet Noise",
"author": [
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Turbulent jet noise is a controversial fluid mechanical puzzle that has amused and bewildered researchers for more than half a century. Whereas numerical simulations are now capable of simultaneously predicting turbulence and its\nradiated sound, the theoretical framework that would guide noise-control efforts is incomplete. Wave packets are intermittent, advecting disturbances that are correlated over distances far exceeding the integral scales of turbulence. Their signatures are readily distinguished in the vortical, turbulent region; the irrotational, evanescent near field; and the propagating far field. We review evidence of the existence, energetics, dynamics, and acoustic efficiency of wave packets. We highlight how extensive data available from simulations and modern measurement techniques can be used to distill acoustically relevant turbulent motions. The evidence supports theories that seek to represent wave packets as instability waves, or more general modal solutions of the governing equations, and confirms the acoustic importance of these structures in the aft-angle radiation of high subsonic and supersonic\njets. The resulting unified view of wave packets provides insights that can help guide control strategies.",
"doi": "10.1146/annurev-fluid-011212-140756",
"issn": "0066-4189",
"publisher": "Annual Reviews",
"publication": "Annual Review of Fluid Mechanics",
"publication_date": "2013-01",
"volume": "45",
"pages": "173-195"
},
{
"id": "authors:3kaja-vga24",
"collection": "authors",
"collection_id": "3kaja-vga24",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130719-124326298",
"type": "book_section",
"title": "Shock Propagation in Polydisperse Bubbly Liquids",
"book_title": "Bubble Dynamics and Shock Waves",
"author": [
{
"family_name": "Ando",
"given_name": "Keita",
"clpid": "Ando-Keita"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "Christopher E.",
"clpid": "Brennen-C-E"
}
],
"contributor": [
{
"family_name": "Delale",
"given_name": "Can F.",
"clpid": "Delale-C-F"
}
],
"abstract": "We investigate the shock dynamics of liquid flows containing small gas bubbles with numerical simulations based on a continuum bubbly flow model. Particular attention is devoted to the effects of distributed bubble sizes and gas-phase nonlinearity on shock dynamics. Ensemble-averaged conservation laws for polydisperse bubbly flows are closed with a Rayleigh\u2013Plesset-type model for single bubble dynamics. Numerical simulations of one-dimensional shock propagation reveal that phase cancellations in the oscillations of different-sized bubbles can lead to an apparent damping of the averaged shock dynamics. Experimentally, we study the propagation of waves in a deformable tube filled with a bubbly liquid. The model is extended to quasi-one-dimensional cases. This leads to steady shock relations that account for the compressibility associated with tube deformation, bubbles and host liquid. A comparison between the theory and the water-hammer experiments suggests that the gas-phase nonlinearity plays an essential role in the propagation of shocks.",
"doi": "10.1007/978-3-642-34297-4_5",
"isbn": "9783642342967",
"publisher": "Springer",
"place_of_publication": "Heidelberg",
"publication_date": "2013",
"pages": "141-175"
},
{
"id": "authors:4wvjz-stn24",
"collection": "authors",
"collection_id": "4wvjz-stn24",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20130201-102028177",
"type": "article",
"title": "The impulse response of a high-speed jet forced with localized arc filament plasma actuators",
"author": [
{
"family_name": "Sinha",
"given_name": "Aniruddha",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Alkandry",
"given_name": "Hind",
"clpid": "Alkandry-H"
},
{
"family_name": "Kearney-Fischer",
"given_name": "Martin",
"clpid": "Kearney-Fischer-M"
},
{
"family_name": "Samimy",
"given_name": "Mo",
"clpid": "Samimy-M"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We present experimental and theoretical analyses of the response of high-speed, high-Reynolds-number, round jets to impulsive forcing with arc-filament-plasma actuators. The impulse response is obtained with forcing Strouhal numbers, based on the nozzle exit diameter and exit center line velocity, less than 0.1. The resulting phase-averaged near-field pressure signature displays a compact wave with a positive peak preceding a negative one, indicative of a large scale structure in the shear layer of the jet. Scaling laws derived by operating the jet at four subsonic Mach numbers are used to distinguish this hydrodynamic component of the phase-averaged jet response from the direct actuator noise. As the forcing frequency increases, the compact waves in the near-field pressure signal overlap each other, indicating interaction of the growing seeded structures. For this regime, the phase-averaged response is approximately replicated by linear superposition of the impulse response, thereby demonstrating the quasi-linearity of structure interaction. A novel application of linear parabolized stability theory yields a successful model of the impulse response.",
"doi": "10.1063/1.4772191",
"issn": "1070-6631",
"publisher": "American Institute of Physics",
"publication": "Physics of Fluids",
"publication_date": "2012-12",
"series_number": "12",
"volume": "24",
"issue": "12",
"pages": "Art. No. 125104"
},
{
"id": "authors:vpge7-w5b95",
"collection": "authors",
"collection_id": "vpge7-w5b95",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112321414",
"type": "conference_item",
"title": "Wavepackets in the velocity field of turbulent jets",
"author": [
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Rodr\u00edguez",
"given_name": "Daniel",
"clpid": "Rodr\u00edguez-D"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Gervais",
"given_name": "Yves",
"clpid": "Gervais-Y"
}
],
"abstract": "We study the velocity field of unforced, high Reynolds number, subsonic jets, issuing from round nozzles with turbulent boundary layers. The objective of the study is to discern the presence of instability waves in such flows and to explore their relationship with the radiated sound. The velocity field is measured using a hot-wire anemometer and a stereoscopic, time-resolved, PIV system, the latter being setup so as to measure three components of velocity in cross-stream planes; the field can thereby be decomposed into frequency and azimuthal Fourier modes. The low-angle sound radiation is measured, synchronously with the PIV acquisition, using a microphone ring array at polar angle, \u03b8 = 20\u00b0 (measured with respect to the downstream jet axis).\n\nConsistent with previous observations, the azimuthal wavenumber spectra of the velocity and acoustic pressure fields are quite different. The velocity spectrum exhibits a peak at higher azimuthal wavenumber and the peak is found to scale with the local momentum thickness of the mixing layer. The acoustic pressure field is, on the other hand, predominantly axisymmetric, suggesting an increased relative acoustic efficiency of the axisymmetric mode of the velocity field, a characteristic that can be shown, theoretically, to be due to the radial compactness of the flow. This is confirmed by significant correlations, around 10%, between the axisymmetric modes of the velocity and acoustic pressure fields, these values being significantly higher than those previously reported for two-point flow-acoustic correlations in subsonic jets. The axisymmetric and first helical modes of the velocity field are then compared with solutions of linear Parabolised Stability Equations (PSE) (where the experimental mean velocity field is used as the base flow) to ascertain if these modes correspond to linear instability waves. For all but the lowest frequencies close agreement is obtained for the spatial amplification, up to the end of the potential core. The radial shapes of the linear PSE results also agree with the experimental results over the same region. The results suggests that, despite the broadband character of the turbulence of these unforced jets, the evolution of a certain range of frequencies and azimuthal modes can be modelled as linear instabilities of the mean velocity profile, and that these instabilities are associated with the sound radiated at low polar angles.",
"doi": "10.2514/6.2012-2115",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2012-11-11"
},
{
"id": "authors:vwpsz-ree22",
"collection": "authors",
"collection_id": "vwpsz-ree22",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112320535",
"type": "conference_item",
"title": "An Analysis of Dispersion and Dissipation Properties of Hermite Methods and Its Application to Direct Numerical Simulation of Jet Noise",
"author": [
{
"family_name": "Jang",
"given_name": "Chang Young",
"clpid": "Jang-Chang-Young"
},
{
"family_name": "Appel\u00f6",
"given_name": "Daniel",
"clpid": "Appel\u00f6-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Hagstrom",
"given_name": "Thomas",
"clpid": "Hagstrom-T"
},
{
"family_name": "Inkman",
"given_name": "Matthew",
"clpid": "Inkman-M"
}
],
"abstract": "The dissipative and dispersive properties of Hermite methods are analyzed by a modified equation approach and by direct computation of the dispersion relations for the discrete modes of the scheme. The two approaches lead to the same results for well-resolved modes but are quantitatively different at the finest scales. The resolution requirements, obtained from the analysis, for Hermite schemes are compared to those of typical high-resolution difference formulas. The results from the analysis are also used to predict the resolution requirements for a simulation at Re \u223c 3600. The validity of the prediction is confirmed by numerical experiments.",
"doi": "10.2514/6.2012-2240",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2012-11-11"
},
{
"id": "authors:62n9f-7f238",
"collection": "authors",
"collection_id": "62n9f-7f238",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112321277",
"type": "conference_item",
"title": "Low-speed jet dynamics and sound radiation",
"author": [
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Violato",
"given_name": "Daniele",
"clpid": "Violato-D"
},
{
"family_name": "Rodr\u00edguez",
"given_name": "Daniel",
"clpid": "Rodr\u00edguez-D"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Scarano",
"given_name": "Fulvio",
"clpid": "Scarano-F"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Gervais",
"given_name": "Yves",
"clpid": "Gervais-Y"
}
],
"abstract": "Experimental velocity measurements of a low-speed jet, performed using time-resolved tomographic PIV, are used to study the dynamics of large-scale structures and their sound radiation. The experimental results show the roll-up of axisymmetric vortices that pair downstream, and subsequently lose their azimuthal coherence. Models of linear instability waves using both steady laminar and mean-field base flows flow are applied. While good agreement can be obtained for the vortex roll-up frequency in the near-nozzle region using the laminar base flow, non-linear effects must be included, via the mean field, in order to capture the downstream evolution of both the fundamental and subharmonic (vortex pairing). The velocity fluctuations for both frequencies have a wave-packet structure with some jitter in the form of modulations of the spatial extent and amplitude of the envelope. The sound radiation is modelled using a jittering wave-packet model, an shows agreement with the exponential directivity shape of Laufer and Yen (J. Fluid Mech. 134, 1983).",
"doi": "10.2514/6.2012-2080",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2012-11-11"
},
{
"id": "authors:3err5-ynj11",
"collection": "authors",
"collection_id": "3err5-ynj11",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112323257",
"type": "conference_item",
"title": "Parabolized stability equation models in turbulent supersonic jets",
"author": [
{
"family_name": "Rodr\u00edguez",
"given_name": "Daniel",
"clpid": "Rodr\u00edguez-D"
},
{
"family_name": "Sinha",
"given_name": "Aniruddha",
"orcid": "0000-0002-7122-3549",
"clpid": "Sinha-A"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The peak noise radiation in the aft direction of high-speed, turbulent jets has been linked to the dynamics of the large-scale structures. We use the parabolized stability equations (PSE) to model these structures as wavepackets associated with instability of the turbulent mean flow. Our past work has demonstrated the utility of these models for subsonic jets; in the present work we extend these methods to supersonic jets. A large eddy simulation database corresponding to an unheated, ideally-expanded Mach 1.5 jet with Reynolds number of 300,000 is employed to extract the necessary input for the PSE (the mean flow and initial conditions) and also to perform comparisons and validations of the computed wavepackets.\n\nBy contrast with subsonic jets, when the jet exit velocity is supersonic with respect to the ambient speed of sound, linear stability theory predicts that multiple instability modes, related to resonance of pressure waves within the potential core, can be present in addition to the inflectional instability. The possible coexistence of different instability mechanisms, the determination of adequate inlet conditions, and their effect on the wavepackets computed are investigated here.\n\nWe compare the wavepackets predicted by PSE with fluctuations extracted from the LES data. When performing comparisons, filtering techniques need to be employed in order to extract the coherent, low frequency structures associated with wavepackets. Largescale fluctuations educed using cross-correlation techniques, such as the proper orthogonal decomposition, are shown to compare reasonably well with the PSE wavepackets, but by contrast with subsonic jets, it appears that several POD modes are required to represent the PSE-predicted wavepacket.",
"doi": "10.2514/6.2012-2117",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2012-11-11"
},
{
"id": "authors:2czvw-bpz81",
"collection": "authors",
"collection_id": "2czvw-bpz81",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20121211-102852653",
"type": "article",
"title": "Simulation and Cryogenic Experiments of Natural\n Convection for the Titan Montgolfiere",
"author": [
{
"family_name": "Feldman",
"given_name": "Yuri",
"clpid": "Feldman-Y"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Pauken",
"given_name": "Michael T.",
"orcid": "0000-0002-3993-675X",
"clpid": "Pauken-M-T"
},
{
"family_name": "Hall",
"given_name": "Jeffrey L.",
"clpid": "Hall-J-L"
},
{
"family_name": "Jones",
"given_name": "Jack A.",
"clpid": "Jones-J-A"
}
],
"abstract": "Natural convection in a spherical geometry is considered for prediction of the buoyancy of single- and double-walled\nballoons in a cryogenic environment such as Titan's atmosphere. The steady-state flow characteristics\nobtained by solving the Reynolds-averaged Navier\u2013Stokes equations with a standard turbulence model are used to\ndetermine the net buoyancy as a function of heat input. Thermal radiation effects are shown to have a minor impact\non the buoyancy, as would be expected at cryogenic conditions. The predicted buoyancy and temperature fields\ncompare favorably with experiments preformed on a 1-m-diameter Montgolfiere prototype in a cryogenic facility. In\naddition, both numerical and experimental results were compared with correlations for the heat transfer coefficients\nfor free convection internal and external to the balloon as well as in the concentric gap of the double-walled balloons.\nFinally, scaling issues related to inferring the performance of the full-scale Montgolfiere from the model-scale results\nare examined.",
"doi": "10.2514/1.J051672",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2012-11",
"series_number": "11",
"volume": "50",
"issue": "11",
"pages": "2483-2491"
},
{
"id": "authors:hne5z-85q52",
"collection": "authors",
"collection_id": "hne5z-85q52",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112323497",
"type": "conference_item",
"title": "Numerical Modeling and Analysis of Early Shock Wave Interactions with a Dense Particle Cloud",
"author": [
{
"family_name": "Regele",
"given_name": "J. D.",
"clpid": "Regele-J-D"
},
{
"family_name": "Rabinovitch",
"given_name": "J.",
"orcid": "0000-0002-1914-7964",
"clpid": "Rabinovitch-J"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Blanquart",
"given_name": "G.",
"orcid": "0000-0002-5074-9728",
"clpid": "Blanquart-G"
}
],
"abstract": "Dense compressible multiphase flows exist in variable phase turbines, explosions, and fluidized beds, where the particle volume fraction is in the range 0.001 < \u03b1_d < 0.5. A simple model problem that can be used to study modeling issues related to these types of flows is a shock wave impacting a particle cloud. In order to characterize the initial shock-particle interactions when there is little particle movement, a two-dimensional (2-D) model problem is created where the particles are frozen in place. Qualitative comparison with experimental data indicates that the 2-D model captures the essential flow physics. Volume-averaging of the 2-D data is used to reduce the data to one dimension, and x-t diagrams are used to characterize the flow behavior. An equivalent one-dimensional (1-D) model problem is developed for direct comparison with the 2-D model. While the 1-D model characterizes the overall steady-state flow behavior well, it fails to capture aspects of the unsteady behavior. As might be expected, it is found that neglecting the unclosed fluctuation terms inherent in the volume-averaged equations is not appropriate for dense gas-particle flows.",
"doi": "10.2514/6.2012-3161",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2012-09-06"
},
{
"id": "authors:kyz36-qkt52",
"collection": "authors",
"collection_id": "kyz36-qkt52",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120817-102356325",
"type": "article",
"title": "Axisymmetric superdirectivity in subsonic jets",
"author": [
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Gervais",
"given_name": "Yves",
"clpid": "Gervais-Y"
}
],
"abstract": "We present experimental results for the acoustic field of jets with Mach numbers\nbetween 0.35 and 0.6. An azimuthal ring array of six microphones, whose polar\nangle, \u03b8, was progressively varied, allows the decomposition of the acoustic pressure\ninto azimuthal Fourier modes. In agreement with past observations, the sound field for\nlow polar angles (measured with respect to the jet axis) is found to be dominated by\nthe axisymmetric mode, particularly at the peak Strouhal number. The axisymmetric\nmode of the acoustic field can be clearly associated with an axially non-compact\nsource, in the form of a wavepacket: the sound pressure level for peak frequencies is\nfound be superdirective for all Mach numbers considered, with exponential decay as a\nfunction of (1 \u2013 M_c cos \u03b8)^2, where M_c is the Mach number based on the phase velocity\nU_c of the convected wave. While the mode m = 1 spectrum scales with Strouhal\nnumber, suggesting that its energy content is associated with turbulence scales,\nthe axisymmetric mode scales with Helmholtz number \u2013 the ratio between source\nlength scale and acoustic wavelength. The axisymmetric radiation has a stronger\nvelocity dependence than the higher-order azimuthal modes, again in agreement with\npredictions of wavepacket models. We estimate the axial extent of the source of\nthe axisymmetric component of the sound field to be of the order of six to eight\njet diameters. This estimate is obtained in two different ways, using, respectively,\nthe directivity shape and the velocity exponent of the sound radiation. The analysis\nfurthermore shows that compressibility plays a significant role in the wavepacket\ndynamics, even at this low Mach number. Velocity fluctuations on the jet centreline\nare reduced as the Mach number is increased, an effect that must be accounted for\nin order to obtain a correct estimation of the velocity dependence of sound radiation.\nFinally, the higher-order azimuthal modes of the sound field are considered, and a\nmodel for the low-angle sound radiation by helical wavepackets is developed. The\nmeasured sound for azimuthal modes 1 and 2 at low Strouhal numbers is seen to\ncorrespond closely to the predicted directivity shapes.",
"doi": "10.1017/jfm.2012.247",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2012-08-10",
"volume": "704",
"pages": "388-420"
},
{
"id": "authors:jhk09-xsf32",
"collection": "authors",
"collection_id": "jhk09-xsf32",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112321189",
"type": "book_section",
"title": "Investigation of a New Model for Bubbly Cavitating Flow",
"book_title": "Proceedings of the 8th International Symposium on Cavitation",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Fuster",
"given_name": "Daniel",
"clpid": "Fuster-D"
}
],
"contributor": [
{
"family_name": "Ohl",
"given_name": "Claus-Dieter",
"clpid": "Ohl-C-D"
},
{
"family_name": "Klaseboer",
"given_name": "Evert",
"clpid": "Klaseboer-E"
},
{
"family_name": "Ohl",
"given_name": "Siew Wan",
"clpid": "Ohl-Siew-Wan"
},
{
"family_name": "Gong",
"given_name": "Shi Wei",
"clpid": "Gong-Shi-Wei"
},
{
"family_name": "Khoo",
"given_name": "B. C.",
"clpid": "Khoo-B-C"
}
],
"abstract": "A new model for bubbly, cavitating flow is validated and used to study the shock-induced oscillations of bubble clouds arising in shockwave lithotripsy and other applications. Compared to previous models based on volume and phase averaging, the new model extends the range of void fractions that can be reliably simulated and, for appropriately low void fractions, reproduces the results of the polydisperse phase-averaged model with much smaller computational expense.",
"isbn": "9789810728267",
"publisher": "Research Publishing Services",
"place_of_publication": "Singapore",
"publication_date": "2012-08",
"pages": "26-30"
},
{
"id": "authors:jhgkz-esh83",
"collection": "authors",
"collection_id": "jhgkz-esh83",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120807-103744882",
"type": "article",
"title": "Effects of Actuation Frequency on Flow Control Applied to a Wall-Mounted Hump",
"author": [
{
"family_name": "Franck",
"given_name": "Jennifer A.",
"clpid": "Franck-J-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Active flow control, and particularly unsteady mass injection (synthetic jets), promotes reattachment of naturally separated flows and can increase lift and decrease drag on airfoils at high angles of attack. Synthetic-jet actuators are typically characterized by the\nunsteady momentum coefficient =(\u03c1_sh_s)/(0.5\u03c1_(\u221e)U^2_(\u221e)c) and the actuation frequency F^(+)= fX_sep/U_\u221e, where \u03c1_s and u_s are the density and velocity of the injected fluid, respectively; h_s is the slot velocity; f is the actuation frequency; and X_sep is the separation distance or chord length, depending on the author or application. Actuation frequencies are often chosen to be on the order of the natural large-scale shedding frequency, or F^(+) ~ O(1). At this frequency, large-scale vortex shedding is induced, which increases the entrainment rate and promotes deflection of the separated shear layer toward the surface. Recent investigations have looked at a second regime of actuation frequencies, which are typically an order of magnitude higher than the most dominant natural frequency in the separated flow and are designed to excite Kelvin\u2013Helmholtz instabilities in the boundary layer. In the airfoil experiments of Amitay and Glezer and Glezer et al., high-frequency excitation was found to be more effective in improving the aerodynamic performance than actuation at lower frequencies by increasing the suction force immediately after the leading edge actuation location. Simulations performed by Visbal and Visbal et al. have shown that plasma-based actuation pulsed at frequencies in the range of F^(+) = 4\u20138 are effective in promoting laminar-turbulent transition and suppressing separation. However, when applied to a fully turbulent boundary layer, the plasma actuation required significantly more power to achieve a reduction in separation bubble size. Other airfoil simulations at low or transitional Reynolds number have found that actuation close to the fundamental shear-layer frequency is ineffective, and forcing closest to the natural shedding frequency is more optimal; however, such two-dimensional simulations may not be accurately capturing the three-dimensional flow physics. Similar results are seen in the numerical experiments by Dandois et al. on a backward-facing step, in which the separation bubble length increased with high-frequency forcing. \nHere, we briefly report results for a compressible, large-eddy simulation (LES) of flow past a wall-mounted hump at high Reynolds number where oscillatory control is applied at F^(+) ~ O(10). The LES with F^(+) ~ O(1) was previously validated and found to compare favorably with extensive experimental results of this geometry. Many other computational results in the low-frequency regime were reported in the NASA Langley Computational Fluid Dynamics Validation workshop. We simulate the flow at Re_c = 500,000 and Mach numbers of 0.25 and 0.6, the latter of which is significantly higher than previous simulations of high-frequency actuation.",
"doi": "10.2514/1.J051183",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2012-07",
"series_number": "7",
"volume": "50",
"issue": "7",
"pages": "1631-1634"
},
{
"id": "authors:9nd7s-k7a09",
"collection": "authors",
"collection_id": "9nd7s-k7a09",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112320617",
"type": "conference_item",
"title": "Simulation of compressible flows using Hermite methods",
"author": [
{
"family_name": "Hagstrom",
"given_name": "Thomas",
"clpid": "Hagstrom-T"
},
{
"family_name": "Appel\u00f6",
"given_name": "Daniel",
"clpid": "Appel\u00f6-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Inkman",
"given_name": "Matthew",
"clpid": "Inkman-M"
},
{
"family_name": "Jang",
"given_name": "Chang Young",
"clpid": "Jang-Chang-Young"
}
],
"abstract": "Spectral element methods based on Hermite interpolation have a number of unique properties. First of all, the stabilization inherent in the interpolation process is sufficient to suppress nonlinear instabilities observed with other discretization schemes and leads to accurate linear transport of nonsmooth solutions. Second, and most important, they allow purely local time-stepping procedures limited only by geometric domain-of-dependence requirements. Thus high-order Hermite methods maximize the computation-to-communication ratio and therefore they admit highly efficient implementations on multicore processors. In this talk we focus on the application of Hermite methods to simulate unsteady compressible flows. Examples will include the direct simulation of the aeroacoustics of a low Reynolds number subsonic jet, as well as studies of more basic sound radiating flows. The latter will illustrate the coupling of Hermite methods with more standard discontinuous Galerkin discretizations to handle physical boundaries.",
"doi": "10.1121/1.4708863",
"publication_date": "2012-04-12"
},
{
"id": "authors:zep0t-v3004",
"collection": "authors",
"collection_id": "zep0t-v3004",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112320367",
"type": "book_section",
"title": "Effects of Target Compliance on a High-Speed Droplet Impact",
"book_title": "Ultra Clean Processing of Semiconductor Surfaces X",
"author": [
{
"family_name": "Sanada",
"given_name": "Toshiyuki",
"clpid": "Sanada-Toshiyuki"
},
{
"family_name": "Ando",
"given_name": "Keita",
"clpid": "Ando-Keita"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "Mertens",
"given_name": "Paul",
"clpid": "Mertens-Paul"
},
{
"family_name": "Meuris",
"given_name": "Marc",
"clpid": "Meuris-Marc"
},
{
"family_name": "Heyns",
"given_name": "Marc",
"clpid": "Heyns-Marc"
}
],
"abstract": "High speed spray cleaning which utilize droplets impact has been used for removing contaminants from wafer surface. When a droplet impacts a solid surface at high speed, the contact periphery expands very quickly and liquid compressibility plays an important role in the initial dynamics and the formation of lateral jets. Impact results in high pressures that can clean or damage the surface. In this study, we numerically investigated a high speed droplet impacts on a solid wall. In order to compare the available theory and experiments, 1 D, 2D and axisymmetric solutions are obtained. The generated pressures, shock speeds, and the lateral jetting mechanism are investigated; especially the effect of target compliance is focused.",
"doi": "10.4028/www.scientific.net/SSP.187.137",
"isbn": "9783037853887",
"publisher": "Trans Tech Publications",
"place_of_publication": "Switzerland",
"publication_date": "2012-04",
"pages": "137-140"
},
{
"id": "authors:2pqy6-0g834",
"collection": "authors",
"collection_id": "2pqy6-0g834",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120224-125133227",
"type": "article",
"title": "A contact model for normal immersed collisions between a particle and a wall",
"author": [
{
"family_name": "Li",
"given_name": "Xiaobai",
"clpid": "Li-Xiaobai"
},
{
"family_name": "Hunt",
"given_name": "Melany L.",
"orcid": "0000-0001-5592-2334",
"clpid": "Hunt-M-L"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The incompressible Navier\u2013Stokes equations are solved numerically to predict the coupled motion of a falling particle and the surrounding fluid as the particle impacts and rebounds from a planar wall. The method is validated by comparing the numerical simulations of a settling sphere with experimental measurements of the sphere trajectory and the accompanying flow field. The normal collision process is then studied for a range of impact Stokes numbers. A contact model of the liquid\u2013solid interaction and elastic effect is developed that incorporates the elasticity of the solids to permit the rebound trajectory to be simulated accurately. The contact model is applied when the particle is sufficiently close to the wall that it becomes difficult to resolve the thin lubrication layer. The model is calibrated with new measurements of the particle trajectories and reproduces the observed coefficient of restitution over a range of impact Stokes numbers from 1 to 1000.",
"doi": "10.1017/jfm.2011.461",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2012-01-25",
"volume": "691",
"pages": "123-145"
},
{
"id": "authors:0sr9j-09p72",
"collection": "authors",
"collection_id": "0sr9j-09p72",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120203-100537724",
"type": "article",
"title": "Instability wave models for the near-field fluctuations of turbulent jets",
"author": [
{
"family_name": "Gudmundsson",
"given_name": "K.",
"clpid": "Gudmundsson-K"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Previous work has shown that aspects of the evolution of large-scale structures, particularly in forced and transitional mixing layers and jets, can be described by linear and nonlinear stability theories. However, questions persist as to the choice of the basic (steady) flow field to perturb, and the extent to which disturbances in natural (unforced), initially turbulent jets may be modelled with the theory. For unforced jets, identification is made difficult by the lack of a phase reference that would permit a portion of the signal associated with the instability wave to be isolated from other, uncorrelated fluctuations. In this paper, we investigate the extent to which pressure and velocity fluctuations in subsonic, turbulent round jets can be described as linear perturbations to the mean flow field. The disturbances are expanded about the experimentally measured jet mean flow field, and evolved using linear parabolized stability equations (PSE) that account, in an approximate way, for the weakly non-parallel jet mean flow field. We utilize data from an extensive microphone array that measures pressure fluctuations just outside the jet shear layer to show that, up to an unknown initial disturbance spectrum, the phase, wavelength, and amplitude envelope of convecting wavepackets agree well with PSE solutions at frequencies and azimuthal wavenumbers that can be accurately measured with the array. We next apply the proper orthogonal decomposition to near-field velocity fluctuations measured with particle image velocimetry, and show that the structure of the most energetic modes is also similar to eigenfunctions from the linear theory. Importantly, the amplitudes of the modes inferred from the velocity fluctuations are in reasonable agreement with those identified from the microphone array. The results therefore suggest that, to predict, with reasonable accuracy, the evolution of the largest-scale structures that comprise the most energetic portion of the turbulent spectrum of natural jets, nonlinear effects need only be indirectly accounted for by considering perturbations to the mean turbulent flow field, while neglecting any non-zero frequency disturbance interactions.",
"doi": "10.1017/jfm.2011.401",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2011-12-25",
"volume": "689",
"pages": "97-128"
},
{
"id": "authors:9mnz8-y5059",
"collection": "authors",
"collection_id": "9mnz8-y5059",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111221-123516479",
"type": "conference_item",
"title": "Shock Theory of a Bubbly Liquid in a Deformable Tube",
"author": [
{
"family_name": "Ando",
"given_name": "K.",
"clpid": "Ando-Keita"
},
{
"family_name": "Sanada",
"given_name": "T.",
"clpid": "Sanada-T"
},
{
"family_name": "Inaba",
"given_name": "K.",
"clpid": "Inaba-Kazuaki"
},
{
"family_name": "Shepherd",
"given_name": "J. E.",
"orcid": "0000-0003-3181-9310",
"clpid": "Shepherd-J-E"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "C. E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "Shock propagation through a bubbly liquid filled in a deformable cylindrical tube is considered. Quasi-one-dimensional\nbubbly flow equations that include fluid-structure interaction are formulated, and the steady shock\nrelations are derived. Experiments are conducted in which a free-falling steel projectile impacts the top of an air/water\nmixture in a polycarbonate tube, and stress waves in the tube material are measured. The experimental data indicate\nthat the linear theory cannot properly predict the propagation speeds of shock waves in mixture-filled tubes; the shock\ntheory is found to more accurately estimate the measured wave speeds.",
"publisher": "Caltech Library",
"publication_date": "2011-12-21"
},
{
"id": "authors:f8vna-mxz22",
"collection": "authors",
"collection_id": "f8vna-mxz22",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20111213-124427981",
"type": "conference_item",
"title": "Shock propagation in polydisperse bubbly flows",
"author": [
{
"family_name": "Ando",
"given_name": "Keita",
"clpid": "Ando-Keita"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "Christopher E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "The effect of distributed bubble size on shock propagation\nin homogeneous bubbly liquids is computed using a continuum\ntwo-phase model. An ensemble-averaging technique is employed\nto derive the statistically averaged equations and a finite-volume\nmethod is used to solve the model equations. The bubble\ndynamics are incorporated using a Rayleigh-Plesset-type equation\nwhich includes the effects of heat transfer, liquid viscosity\nand compressibility. For the case of monodisperse bubbles, it is\nknown that relaxation oscillations occur behind the shock due to\nthe bubble dynamics. The present computations for the case of\npolydisperse bubbles show that bubble size distributions lead to\nadditional damping of the shock dynamics. If the distribution is\nsufficiently broad, the statistical effect dominates over the physical\ndamping associated with the single bubble dynamics. This\nsmooths out the oscillatory shock structure.",
"publisher": "Caltech Library",
"publication_date": "2011-12-13"
},
{
"id": "authors:4mgnf-w2x74",
"collection": "authors",
"collection_id": "4mgnf-w2x74",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120123-141053654",
"type": "article",
"title": "Modelling bubble clusters in compressible liquids",
"author": [
{
"family_name": "Fuster",
"given_name": "D.",
"clpid": "Fuster-D"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We present a new model for bubbly cavitating flows. Based on volume-averaged equations, a subgrid model is added to account for a bubble, or multiple bubbles, within each computational cell. The model converges to the solution of ensemble-averaged bubbly flow equations for weak oscillations and monodisperse systems. In the other extreme, it also converges to the theoretical solution for a single oscillating bubble, and captures the bubble radius evolution and the pressure disturbance induced in the liquid. A substantial saving of computational time is achieved compared to ensemble-averaged models for polydisperse mixtures.",
"doi": "10.1017/jfm.2011.380",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2011-12",
"volume": "688",
"pages": "352-389"
},
{
"id": "authors:0bwnw-d3f06",
"collection": "authors",
"collection_id": "0bwnw-d3f06",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102319028",
"type": "conference_item",
"title": "Numerical and Experimental Modeling of Natural Convection for a Cryogenic Prototype of a Titan Montgolfiere",
"author": [
{
"family_name": "Feldman",
"given_name": "Yu.",
"clpid": "Feldman-Yu"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Pauken",
"given_name": "M.",
"orcid": "0000-0002-3993-675X",
"clpid": "Pauken-M-T"
},
{
"family_name": "Hall",
"given_name": "J. L.",
"clpid": "Hall-J-L"
},
{
"family_name": "Jones",
"given_name": "J. A.",
"clpid": "Jones-J-A"
}
],
"abstract": "Natural convection in a spherical geometry is considered for prediction of the buoyancy characteristics of one meter diameter single- and double-walled balloons in a cryogenic environment. The steady-state flow characteristics obtained by solving the Reynolds-Averaged Navier Stokes equations (RANS) with a standard k-\u03b5 model are used to determine the balloon performance in terms of net buoyancy as a function of heat input. Thermal radiation effects on the overall balloon performance are also investigated. The results obtained compared favorably with the corresponding cryogenic experiments conducted at the same scale in a cryogenic facility. In addition, both numerical and experimental results were compared with engineering heat transfer correlations used in system-level models of the Titan Montgolfiere. Finally, we examine scaling issues for the full-scale Titan Montgolfieres.",
"doi": "10.2514/6.2011-6869",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2011-09"
},
{
"id": "authors:brzft-41e74",
"collection": "authors",
"collection_id": "brzft-41e74",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110908-120901325",
"type": "article",
"title": "Closed-Loop Control of Lift for Longitudinal Gust Suppression\n at Low Reynolds Numbers",
"author": [
{
"family_name": "Kerstens",
"given_name": "Wesley",
"clpid": "Kerstens-W"
},
{
"family_name": "Pfeiffer",
"given_name": "Jens",
"clpid": "Pfeiffer-J"
},
{
"family_name": "Williams",
"given_name": "David",
"clpid": "Williams-D"
},
{
"family_name": "King",
"given_name": "Rudibert",
"clpid": "King-R"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "Naguib",
"given_name": "A.",
"clpid": "Naguib-A"
}
],
"abstract": "Experiments are conducted to investigate the ability of variable-pressure pulsed-blowing actuation to maintain a\nconstant lift force on a low-aspect-ratio semicircular wing in a longitudinally gusting flow. Dynamic models of the lift\nresponse to actuation and the lift response to longitudinal gusting are obtained through modern system identification\nmethods. Robust closed-loop controllers are synthesized using a mixed-sensitivity loop-shaping approach. An\nadditional feedforward disturbance compensator is designed based on a model of the unsteady aerodynamics. The\ncontrollers show suppression of lift fluctuations at low gust frequencies, f < 0.8 Hz(reduced frequency, k < 0.09). At higher frequencies, the control performance degrades due to limitations related to the time for a disturbance, created by the actuators, to convect over the wing and establish the flowfield that leads to enhanced lift on the wing.",
"doi": "10.2514/1.J050954",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2011-08",
"series_number": "8",
"volume": "49",
"issue": "8",
"pages": "1721-1728"
},
{
"id": "authors:qx2a2-rm460",
"collection": "authors",
"collection_id": "qx2a2-rm460",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110812-110736366",
"type": "article",
"title": "Flow around a NACA0018 airfoil with a cavity and its dynamical response to acoustic forcing",
"author": [
{
"family_name": "Olsman",
"given_name": "W. F. J.",
"clpid": "Olsman-W-F-J"
},
{
"family_name": "Willems",
"given_name": "J. F. H.",
"clpid": "Willems-J-F-H"
},
{
"family_name": "Hirschberg",
"given_name": "A.",
"clpid": "Hirschberg-A"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Trieling",
"given_name": "R. R.",
"clpid": "Trieling-R-R"
}
],
"abstract": "Trapping of vortices in a cavity has been explored in recent years as a drag reduction measure for thick airfoils. If, however, trapping fails, then oscillation of\nthe cavity flow may couple with elastic vibration modes of\nthe airfoil. To examine this scenario, the effect of small\namplitude vertical motion on the oscillation of the shear\nlayer above the cavity is studied by acoustic forcing simulating a vertical translation of a modified NACA0018\nprofile. At low Reynolds numbers based on the chord\n(O(10^4)), natural instability modes of this shear layer are\nobserved for Strouhal numbers based on the cavity width of\norder unity. Acoustic forcing sufficiently close to the natural instability frequency induces a strong non-linear\nresponse due to lock-in of the shear layer. At higher Reynolds numbers (above 10^5) for Strouhal number 0.6 or\nlower, no natural instabilities of the shear layer and only a linear response to forcing were observed. The dynamical\npressure difference across the airfoil is then dominated by\nadded mass effects, as was confirmed by numerical simulations.",
"doi": "10.1007/s00348-011-1065-7",
"issn": "0723-4864",
"publisher": "Springer",
"publication": "Experiments in Fluids",
"publication_date": "2011-08",
"series_number": "2",
"volume": "51",
"issue": "2",
"pages": "493-509"
},
{
"id": "authors:y5yf5-3a588",
"collection": "authors",
"collection_id": "y5yf5-3a588",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110713-152954571",
"type": "article",
"title": "Numerical simulation of shock propagation in a polydisperse bubbly liquid",
"author": [
{
"family_name": "Ando",
"given_name": "Keita",
"clpid": "Ando-Keita"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "Christopher E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "The effect of distributed bubble nuclei sizes on shock propagation in a bubbly liquid is numerically investigated. An ensemble-averaged technique is employed to derive the statistically averaged conservation laws for polydisperse bubbly flows. A finite-volume method is developed to solve the continuum bubbly flow equations coupled to a single-bubble-dynamic equation that incorporates the effects of heat transfer, liquid viscosity and compressibility. The one-dimensional shock computations reveal that the distribution of equilibrium bubble sizes leads to an apparent damping of the averaged shock dynamics due to phase cancellations in oscillations of the different-sized bubbles. If the distribution is sufficiently broad, the phase cancellation effect can dominate over the single-bubble-dynamic dissipation and the averaged shock profile is smoothed out.",
"doi": "10.1016/j.ijmultiphaseflow.2011.03.007",
"issn": "0301-9322",
"publisher": "Elsevier",
"publication": "International Journal of Multiphase Flow",
"publication_date": "2011-07",
"series_number": "6",
"volume": "37",
"issue": "6",
"pages": "596-608"
},
{
"id": "authors:2n6sp-51960",
"collection": "authors",
"collection_id": "2n6sp-51960",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102319521",
"type": "conference_item",
"title": "Numerical Simulations of the Transient Flow Response of a 3D, Low-Aspect-Ratio Wing to Pulsed Actuation",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Fares",
"given_name": "Ehab",
"clpid": "Fares-Ehab"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Numerical simulations of the natural and actuated unsteady flow over a three-dimensional low-aspect ratio wing are performed using Lattice Boltzmann method. The LBM simulations match the flow conditions and the detailed wing geometry from previous experiments, including the actuators that are installed internally along the leading edge of the wing. The present study focuses on the transient lift response to short-duration square-wave actuation, for the wing in a uniform flow at five different angles of attack. Overall, both mean and unsteady numerical results show good agreement with the experimental data, in particular at the post-stall angle of attack 19\u00b0, where the maximum lift enhancement occurs. At that angle of attack, the effects of the actuation strength and duration are investigated. In general, the lift response to a single pulse increases with increasing actuator mass-flow rate and pulse duration.",
"doi": "10.2514/6.2011-3440",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2011-06"
},
{
"id": "authors:e99c1-sbs06",
"collection": "authors",
"collection_id": "e99c1-sbs06",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110613-140739970",
"type": "article",
"title": "Feedback control of vortex shedding from an inclined flat plate",
"author": [
{
"family_name": "Joe",
"given_name": "Won Tae",
"clpid": "Joe-Won-Tae"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "MacMynowski",
"given_name": "Douglas G.",
"orcid": "0000-0003-1987-9417",
"clpid": "MacMartin-D-G"
}
],
"abstract": "Open- and closed-loop control of vortex shedding in two-dimensional flow over a flat plate at high\nangle of attack is numerically investigated at a Reynolds number of 300. Unsteady actuation is modeled as\na body force near the leading or trailing edge and is directed either upstream or downstream. For moderate\nangles of attack, sinusoidal forcing at the natural shedding frequency results in phase locking, with a periodic\nvariation of lift at the same frequency, leading to higher unsteady lift than the natural shedding. However, at\nsufficiently high angles of attack, a subharmonic of the forcing frequency is also excited and the average lift\nover the forcing period varies from cycle-to-cycle in a complex manner. It is observed that the periods with the\nhighest averaged lift are associated with particular phase differences between the forcing and the lift, but that\nthis highest-lift shedding cycle is not always stably maintained with open-loop forcing.We design a feedback\nalgorithm to lock the forcing with the phase shift associated with the highest period-averaged lift. It is shown\nthat the compensator results in a stable phase-locked limit cycle for a broader range of forcing frequencies\nthan the open-loop control, and that it is able to stabilize otherwise unstable high-lift limit cycles that cannot\nbe obtained with open-loop control. For example, at an angle of attack of 40\u25e6, the feedback controller can\nincrease the averaged magnitude of force on the plate by 76% and increase the averaged lift coefficient from\n1.33 to 2.43.",
"doi": "10.1007/s00162-010-0204-8",
"issn": "0935-4964",
"publisher": "Springer",
"publication": "Theoretical and Computational Fluid Dynamics",
"publication_date": "2011-06",
"series_number": "1-4",
"volume": "25",
"issue": "1-4",
"pages": "221-232"
},
{
"id": "authors:yy99d-9ep15",
"collection": "authors",
"collection_id": "yy99d-9ep15",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112323337",
"type": "conference_item",
"title": "Parabolized stability equation models for predicting large-scale mixing noise of turbulent round jets",
"author": [
{
"family_name": "Rodr\u00edguez",
"given_name": "D.",
"clpid": "Rodr\u00edguez-D"
},
{
"family_name": "Samanta",
"given_name": "A.",
"clpid": "Samanta-A"
},
{
"family_name": "Cavalieri",
"given_name": "A. V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Jordan",
"given_name": "P.",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
}
],
"abstract": "Parabolized stability equation (PSE) models are being developed to predict the evolution of low-frequency, large-scale wavepacket structures and their radiated sound in highspeed turbulent round jets. Linear PSE wavepacket models were previously shown to be in reasonably good agreement with the amplitude envelope and phase measured using a microphone array placed just outside the jet shear layer. Here we show they also in very good agreement with hot-wire measurements at the jet centerline in the potential core, for a different set of experiments. When used as a model source for acoustic analogy, the predicted far field noise radiation is in reasonably good agreement with microphone measurements for aft angles where contributions from large-scale structures dominate the acoustic field. Nonlinear PSE is then employed in order to determine the relative importance of the mode interactions on the wavepackets. A series of nonlinear computations with randomized initial conditions are use in order to obtain bounds for the evolution of the modes in the natural turbulent jet flow. It was found that nonlinearity has a very limited impact on the evolution of the wavepackets for St \u2265 0.3. Finally, the nonlinear mechanism for the generation of a low-frequency mode as the difference-frequency mode of two forced frequencies is investigated in the scope of the high Reynolds number jets considered in this paper.",
"doi": "10.2514/6.2011-2838",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2011-06"
},
{
"id": "authors:x6w2g-rb975",
"collection": "authors",
"collection_id": "x6w2g-rb975",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110613-112849752",
"type": "article",
"title": "Special issue on global flow instability and control",
"author": [
{
"family_name": "Theofilis",
"given_name": "Vassilis",
"clpid": "Theofilis-V"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "This special issue is intended to provide a snapshot of current research in the area of \"Global Flow Instability and Control\". The original papers, and to a certain extent the topic itself, are intimately linked with the series of symposia by the same name that were held in Crete, Greece, between 2001 and 2009. As members of the organizing committees of the Crete symposia, we invited all past participants to contribute, and all papers were reviewed following the strict standards of the journal. This preface gives a brief historical account of events that have shaped ideas in the field over the past decade, followed by a synopsis of the papers published herein.",
"doi": "10.1007/s00162-010-0217-3",
"issn": "0935-4964",
"publisher": "Springer",
"publication": "Theoretical and Computational Fluid Dynamics",
"publication_date": "2011-06",
"series_number": "1-4",
"volume": "25",
"issue": "1-4",
"pages": "1-6"
},
{
"id": "authors:pgrpf-cnv25",
"collection": "authors",
"collection_id": "pgrpf-cnv25",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112320713",
"type": "conference_item",
"title": "A projection method for multiphase flows",
"author": [
{
"family_name": "Hartmann",
"given_name": "Daniel",
"clpid": "Hartmann-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "An Eulerian projection approach for incompressible variable-density two-phase flows is presented. The Navier-Stokes equations governing these flows are reformulated to take the form of the corresponding equations for the lighter phase with a constant density, which can be efficiently solved using standard numerical methods. The effect of the additional mass in the heavier phase is accounted for by a forcing term, which is determined from the solution of an artificial velocity field. This artificial field is subjected solely to inertial and gravity forces as well as the force coupling the flow field and the artificial field. The phase interface in this purely Eulerian approach is described using the level-set method. Results for two-dimensional simulations of the Rayleigh-Taylor instability are presented to validate the new method.",
"doi": "10.2514/6.2011-3831",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2011-06"
},
{
"id": "authors:938e3-cka41",
"collection": "authors",
"collection_id": "938e3-cka41",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102317504",
"type": "conference_item",
"title": "Hermite Methods for Aeroacoustics: Recent Progress",
"author": [
{
"family_name": "Appel\u00f6",
"given_name": "Daniel",
"clpid": "Appel\u00f6-D"
},
{
"family_name": "Inkman",
"given_name": "Matthew",
"clpid": "Inkman-M"
},
{
"family_name": "Hagstrom",
"given_name": "Thomas",
"clpid": "Hagstrom-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We present recent developments on Hermite methods for aeroacoustic simulations including time-stepping methods, hybridization with discontinuous Galerkin methods for handling of boundary conditions and adaptive implementations. By scaling studies reported below we show that the features unique to Hermite methods have promise to enable efficient exploitation of modern petascale architectures. We also present preliminary computations of turbulent jet noise obtained with the current implementation of our compressible Navier-Stokes solver.",
"doi": "10.2514/6.2011-2757",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2011-06"
},
{
"id": "authors:s1mnq-rnw88",
"collection": "authors",
"collection_id": "s1mnq-rnw88",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102319217",
"type": "conference_item",
"title": "Axisymmetric superdirectivity in subsonic jets",
"author": [
{
"family_name": "Cavalieri",
"given_name": "Andr\u00e9 V. G.",
"orcid": "0000-0003-4283-0232",
"clpid": "Cavalieri-A-V-G"
},
{
"family_name": "Jordan",
"given_name": "Peter",
"orcid": "0000-0001-8576-5587",
"clpid": "Jordan-P"
},
{
"family_name": "Gervais",
"given_name": "Yves",
"clpid": "Gervais-Y"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We present experimental results for the acoustic field of jets in the Mach number range 0.35 \u2264 M \u2264 0.6. Data acquired by means of an azimuthal ring of six microphones, whose polar angle, \u03b8, was progressively varied, is decomposed into azimuthal Fourier modes. In agreement with past observations, the sound field for low polar angles (measured with respect to the jet axis) is found to be dominated by the axisymmetric mode, particularly at the peak Strouhal number. As \u03b8 is increased, modes 1 and 2 become increasingly important and dominate at angles greater than \u03b8 \u2248 30\u00b0. A number of features of the axisymmetric mode of the acoustic field suggest that it can be associated with an axially non-compact source, in the form of a convected wave comprising amplification, saturation and decay, and whose axial extension is of the order of several jet diameters: (a) the sound pressure level for peak frequencies is shown be superdirective for all Mach numbers considered, with exponential decay as a function of (1 \u2212 M_c cos \u03b8)^2, in agreement with wavepacket models for an axially non-compact axisymmetric source; (b) while the mode m = 1 spectrum scales with Strouhal number, suggesting that its energy content is associated with turbulence scales, the axisymmetric mode scales with Helmholtz number\u2014the ratio between source length scale and acoustic wavelength; (c) the axisymmetric radiation has a stronger velocity dependence than the higher order azimuthal modes, again in agreement with predictions of the said wave-packet models. We use such a wave-packet model to estimate that the axial extension of the source structure underpinning the axisymmetric component of the sound field is of the order of 6\u20138 jet diameters, and that the source comprises a convected wave with three spatial oscillations, weighted by a Gaussian envelope; such a source structure is in good agreement with past observations based on coherent structure eduction techniques. The present results show that the narrow-band spectrum of the axisymmetric mode contributes to the appearance of the characteristic jet-noise spectrum at low angles, an effect that becomes more marked as the Mach number is increased.",
"doi": "10.2514/6.2011-2743",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2011-06"
},
{
"id": "authors:0g6nk-bns78",
"collection": "authors",
"collection_id": "0g6nk-bns78",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110328-100709222",
"type": "article",
"title": "Control of vortex shedding on two- and three-dimensional aerofoils",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
}
],
"abstract": "We review and expand on the control of separated flows over flat plates and aerofoils at low Reynolds numbers associated with micro air vehicles. Experimental observations of the steady-state and transient lift response to actuation, and its dependence on the actuator, aerofoil geometry and flow conditions, are discussed and an attempt is made to unify them in terms of their excitation of periodic and transient vortex shedding. We also examine strategies for closed-loop flow and flight control using actuation of leading-edge vortices.",
"doi": "10.1098/rsta.2010.0355",
"issn": "1364-503X",
"publisher": "Royal Society of London",
"publication": "Philosophical Transactions A: Mathematical, Physical and Engineering Sciences",
"publication_date": "2011-04-13",
"series_number": "1940",
"volume": "369",
"issue": "1940",
"pages": "1525-1539"
},
{
"id": "authors:zq6nz-fw005",
"collection": "authors",
"collection_id": "zq6nz-fw005",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102319126",
"type": "conference_item",
"title": "Numerical simulation of bubble dynamics in deformable vessels",
"author": [
{
"family_name": "Coralic",
"given_name": "Vedran",
"clpid": "Coralic-V"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The growth and collapse of cavitation bubbles has been implicated as a potential damage mechanism leading to the rupture of blood vessels in shock wave lithotripsy (SWL) [Bailey et al., in The Fifth International Symposium on Cavitation, Osaka, Japan (2003)]. While this phenomenon has been investigated numerically, the resulting simulations have often assumed some degree of symmetry and have often failed to include a large number of influential physics, such as viscosity, compressibility, surface tension, phase change, and fluid\u2010structure interactions (FSI). We present here our efforts to explore the role that cavitation bubbles play in the rupture of blood vessels in SWL and to improve upon the current state of the numerical approach. We have developed a 3\u2010D, high\u2010order accurate, shock\u2010 and interface\u2010capturing, multicomponent flow algorithm that accounts for the effects of surface tension and FSI. The preliminary results for the case of a bubble collapse, induced by a shock wave lithotripter pulse and occurring inside a deformable vessel, are presented.",
"doi": "10.1121/1.3587690",
"publication_date": "2011-04-08"
},
{
"id": "authors:s7m63-wm447",
"collection": "authors",
"collection_id": "s7m63-wm447",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112323080",
"type": "article",
"title": "Reply by the Authors to G. E. Dorrington",
"author": [
{
"family_name": "Samanta",
"given_name": "Arnab",
"clpid": "Samanta-A"
},
{
"family_name": "Appel\u00f6",
"given_name": "Daniel",
"clpid": "Appel\u00f6-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Nott",
"given_name": "Julian",
"clpid": "Nott-J"
},
{
"family_name": "Hall",
"given_name": "Jeffery",
"clpid": "Hall-J"
}
],
"abstract": "[no abstract]",
"doi": "10.2514/1.J050961",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2011-04",
"series_number": "4",
"volume": "49",
"issue": "4",
"pages": "877-878"
},
{
"id": "authors:5btrz-77q55",
"collection": "authors",
"collection_id": "5btrz-77q55",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110328-100709784",
"type": "article",
"title": "Shock propagation through a bubbly liquid in a deformable tube",
"author": [
{
"family_name": "Ando",
"given_name": "Keita",
"clpid": "Ando-Keita"
},
{
"family_name": "Sanada",
"given_name": "T.",
"clpid": "Sanada-Toshiyuki"
},
{
"family_name": "Inaba",
"given_name": "K.",
"clpid": "Inaba-Kazuaki"
},
{
"family_name": "Damazo",
"given_name": "J. S.",
"orcid": "0000-0002-4155-7177",
"clpid": "Damazo-J-S"
},
{
"family_name": "Shepherd",
"given_name": "J. E.",
"orcid": "0000-0003-3181-9310",
"clpid": "Shepherd-J-E"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "C. E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "Shock propagation through a bubbly liquid contained in a deformable tube is considered. Quasi-one-dimensional mixture-averaged flow equations that include fluid\u2013structure interaction are formulated. The steady shock relations are derived and the nonlinear effect due to the gas-phase compressibility is examined. Experiments\nare conducted in which a free-falling steel projectile impacts the top of an air/water mixture in a polycarbonate tube, and stress waves in the tube material and pressure\non the tube wall are measured. The experimental data indicate that the linear theory is incapable of properly predicting the propagation speeds of finite-amplitude waves\nin a mixture-filled tube; the shock theory is found to more accurately estimate the measured wave speeds.",
"doi": "10.1017/S0022112010005707",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2011-03",
"volume": "671",
"pages": "339-363"
},
{
"id": "authors:snj3z-8ba33",
"collection": "authors",
"collection_id": "snj3z-8ba33",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102318931",
"type": "conference_item",
"title": "Instability of Hypersonic Boundary Layer on a Wall with Resonating Micro-Cavities",
"author": [
{
"family_name": "Fedorov",
"given_name": "Alexander V.",
"clpid": "Fedorov-A-V"
},
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Inkman",
"given_name": "Matthew",
"clpid": "Inkman-M"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Ultrasonically absorptive coatings (UAC) can stabilize the Mack second mode and thereby increase the laminar run on configurations where laminar-turbulent transition is second-mode dominated. Theory indicates that the stabilization effect can be essentially enhanced by increasing the UAC porosity. However, direct numerical simulations (DNS) showed that coatings having closely spaced grooves can trigger a new instability whose growth rate can be larger than that of Mack' second mode. The nature of the new instability is investigated theoretically and numerically. 2D linear DNS and stability analysis are performed for the temporally evolving boundary layer on a flat wall at the outer-flow Mach number 6. The wall is covered by UAC comprising equally-spaced spanwise grooves. It is shown that the new mode is associated with acoustic resonances in the grooves. Disturbance fields near mouths of resonating cavities are coupled such that the boundary-layer disturbance is decelerated and becomes unstable. To avoid this detrimental effect the coating should have sufficiently small porosity and/or narrow pores of sufficiently small aspect ratio. Restrictions on these parameters can be estimated using the linear stability theory with the impedance boundary conditions.",
"doi": "10.2514/6.2011-373",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2011-01"
},
{
"id": "authors:89wpc-7rd03",
"collection": "authors",
"collection_id": "89wpc-7rd03",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110222-101256399",
"type": "article",
"title": "Numerical Simulation of Flow over an Airfoil with a Cavity",
"author": [
{
"family_name": "Olsman",
"given_name": "W. F. J.",
"clpid": "Olsman-W-F-J"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Two-dimensional direct numerical simulation of the flow over a NACA0018 airfoil with a cavity is presented. The\nlow Reynolds number simulations are validated by means of flow visualizations carried out in a water channel. From\nthe simulations, it follows that there are two main regimes of flow inside the cavity. Depending on the angle of attack,\nthe first or the second shear-layer mode (Rossiter tone) is present. The global effect of the cavity on the flow around\nthe airfoil is the generation of vortices that reduce flow separation downstream of the cavity. At high positive angles of\nattack, the flow separates in front of the cavity, and the separated flow interacts with the cavity, causing the\ngeneration of smaller-scale structures and a narrower wake compared with the case when no cavity is present. At\ncertain angles of attack, the numerical results suggest the possibility of a higher lift-to-drag ratio for the airfoil with\ncavity compared with the airfoil without cavity.",
"doi": "10.2514/1.J050542",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2011-01",
"series_number": "1",
"volume": "49",
"issue": "1",
"pages": "143-149"
},
{
"id": "authors:sgx27-00r74",
"collection": "authors",
"collection_id": "sgx27-00r74",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102318132",
"type": "book_section",
"title": "Damage Potential of the Shock-Induced Collapse of a Gas Bubble",
"book_title": "Proceedings of the 7th International Symposium on Cavitation (CAV2009)",
"author": [
{
"family_name": "Johnsen",
"given_name": "Eric",
"clpid": "Johnsen-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Cleveland",
"given_name": "Robin",
"clpid": "Cleveland-R-O"
}
],
"abstract": "Numerical simulations are used to evaluate the damage potential of the shock-induced collapse of a pre-existing gas bubble near a rigid surface. In the context of shock wave lithotripsy, a medical procedure where focused shock waves are used to pulverize kidney stones, shock-induced bubble collapse represents a potential mechanism by which the shock energy directed at the stone may be amplified and concentrated. First the bubble dynamics of shock-induced collapse are discussed. As an indication of the damage potential, the wall pressure is considered. It is found that, for bubbles initially close to the wall, local pressures greater than 1 GPa are achieved. For larger stand-off distances, the wall pressure is inversely proportional to the location of bubble collapse. From this relationship, it is found that bubbles within a certain initial stand-off distance from the wall amplify the pressure of the incoming shock. Furthermore, the extent along the wall over which the pressure due to bubble collapse is higher than that of the pulse is estimated. In addition, the present computational fluid dynamics simulations are used as input into an elastic waves propagation code, in order to investigate the stresses generated within kidney stone in the context of shock wave lithotripsy. The present work shows that the shock-induced collapse of a gas bubble has potential not only for erosion along the stone surface, but also for structural damage within the stone due to internal wave reflection and interference.",
"isbn": "9781617826429",
"publisher": "Curran",
"place_of_publication": "Red Hook, NY",
"publication_date": "2011",
"pages": "473-482"
},
{
"id": "authors:1wweh-1yn35",
"collection": "authors",
"collection_id": "1wweh-1yn35",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322993",
"type": "article",
"title": "A Computational Study of High-Speed Droplet Impact",
"author": [
{
"family_name": "Sanada",
"given_name": "T.",
"clpid": "Sanada-T"
},
{
"family_name": "Ando",
"given_name": "K.",
"clpid": "Ando-Keita"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "When a droplet impacts a solid surface at high speed, the contact periphery expands very quickly and liquid compressibility plays an important role in the initial dynamics and the formation of lateral jets. The high speed impact results in high pressures that can account for the surface erosion. In this study, we numerically investigated a high speed droplet impacts on a solid wall. The multicomponent Euler equations with the stiffened equation of state are computed using a FV-WENO scheme with an HLLC Riemann solver that accurately captures shocks and interfaces. In order to compare the available theories and experiments, 1D, 2D and axisymmetric solutions are obtained. The generated pressures, shock speeds, and differences in the dimensionality are investigated. In addition, the effect of target compliance is evaluated.",
"doi": "10.3970/fdmp.2011.007.329",
"issn": "1555-2578",
"publisher": "Tech Science Press",
"publication": "Fluid Dynamics & Material Processing",
"publication_date": "2011",
"series_number": "4",
"volume": "7",
"issue": "4",
"pages": "329-340"
},
{
"id": "authors:2r3yh-6xy61",
"collection": "authors",
"collection_id": "2r3yh-6xy61",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20101214-085632676",
"type": "article",
"title": "Simulation of the effects of cavitation and anatomy in the shock path of model lithotripters",
"author": [
{
"family_name": "Krimmel",
"given_name": "Jeff",
"clpid": "Krimmel-J"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Tanguay",
"given_name": "Michel",
"clpid": "Tanguay-M"
}
],
"abstract": "We report on recent efforts to develop predictive models for the pressure and other flow variables in the focal region of shock wave lithotripters. Baseline simulations of three representative lithotripters (electrohydraulic, electromagnetic, and piezoelectric) compare favorably with in vitro experiments (in a water bath). We proceed to model and investigate how shock focusing is altered by the presence of material interfaces associated with different types of tissue encountered along the shock path, and by the presence of cavitation bubbles that are excited by tensile pressures associated with the focused shock wave. We use human anatomical data, but simplify the description by assuming that the tissue behaves as a fluid, and by assuming cylindrical symmetry along the shock path. Scattering by material interfaces is significant, and regions of high pressure amplitudes (both compressive and tensile) are generated almost 4 cm postfocus. Bubble dynamics generate secondary shocks whose strength depends on the density of bubbles and the pulse repetition frequency (PRF). At sufficiently large densities, the bubbles also attenuate the shock. Together with experimental evidence, the simulations suggest that high PRF may be counterproductive for stone comminution. Finally, we discuss how the lithotripter simulations can be used as input to more detailed physical models that attempt to characterize the mechanisms by which collapsing cavitation models erode stones, and by which shock waves and bubbles may damage tissue.",
"doi": "10.1007/s00240-010-0332-z",
"pmcid": "PMC3032941",
"issn": "0300-5623",
"publisher": "Springer",
"publication": "Urological Research",
"publication_date": "2010-12",
"series_number": "6",
"volume": "38",
"issue": "6",
"pages": "505-518"
},
{
"id": "authors:kjydr-yaz92",
"collection": "authors",
"collection_id": "kjydr-yaz92",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100831-130506686",
"type": "article",
"title": "Lift Enhancement for Low-Aspect-Ratio Wings with Periodic Excitation",
"author": [
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
},
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
}
],
"abstract": "In an effort to enhance lift on low-aspect-ratio rectangular flat-plate wings in low-Reynolds-number\npost-stall flows, periodic injection of momentum is considered along the trailing edge in this numerical\nstudy. The purpose of actuation is not to reattach the flow but to change the dynamics of the wake\nvortices such that the resulting lift force is increased. Periodic forcing is observed to be effective\nin increasing lift for various aspect ratios and angles of attack, achieving a similar lift enhancement\nattained by steady forcing with less momentum input. Through the investigation on the influence of\nthe actuation frequency, it is also found that there exists a frequency at which the flow locks on to a\ntime-periodic high-lift state.",
"doi": "10.2514/1.J050248",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2010-08",
"series_number": "8",
"volume": "48",
"issue": "8",
"pages": "1785-1790"
},
{
"id": "authors:2xk6c-70w27",
"collection": "authors",
"collection_id": "2xk6c-70w27",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320850",
"type": "book_section",
"title": "Numerical Analysis of High Speed Droplet Impact",
"author": [
{
"family_name": "Sanada",
"given_name": "Toshiyuki",
"clpid": "Sanada-Toshiyuki"
},
{
"family_name": "Ando",
"given_name": "Keita",
"clpid": "Ando-Keita"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "When a droplet impacts a solid surface at high speed, the contact periphery expands very quickly and liquid compressibility plays an important role in the initial dynamics and the formation of lateral jets. The high speed impact results in high pressures that can account for the surface erosion. In this study, we numerically investigated a high speed droplet impacts on a solid wall. The multicomponent Euler equations with the stiffened equation of state are computed using a FV-WENO scheme with an HLLC Riemann solver (Johnsen & Colonius 2006) that accurately captures shocks and interfaces. In order to compare the available theories and experiments, 1D, 2D and axisymmetric solutions are obtained. The generated pressures, shock speeds, and the lateral jetting generation are investigated. In addition, the effect of target compliance is evaluated.",
"publisher": "University of Florida George A. Smathers Libraries",
"publication_date": "2010-06-04"
},
{
"id": "authors:ms51t-fc676",
"collection": "authors",
"collection_id": "ms51t-fc676",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102319855",
"type": "conference_item",
"title": "Closed Loop Control of a Wing's Lift for 'Gust' Suppression",
"author": [
{
"family_name": "Kerstens",
"given_name": "Wesley",
"clpid": "Kerstens-W"
},
{
"family_name": "Williams",
"given_name": "David",
"clpid": "Williams-D"
},
{
"family_name": "Pfeiffer",
"given_name": "Jens",
"clpid": "Pfeiffer-J"
},
{
"family_name": "King",
"given_name": "Rudibert",
"clpid": "King-R"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The ability to maintain a constant lift force on a low aspect ratio semi circular wing using pulsed blowing active flow control is experimentally investigated. Dynamic models of the wing's response to pressure (pulsed blowing) actuation and the response to longitudinal gusting are obtained through black-box system identification methods. Robust closed loop controllers are synthesized using a mixed sensitivity loop shaping approach. An additional feedforward disturbance compensation is designed based on a model of the unsteady aerodynamics. The controllers show good suppression of lift fluctuations at low frequencies, but as frequencies increase the control performance degrades due to fundamental physical limitations. The limitations are related to the leading edge vortex formation time.",
"doi": "10.2514/6.2010-4969",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2010-06"
},
{
"id": "authors:x7naa-sfb78",
"collection": "authors",
"collection_id": "x7naa-sfb78",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102319343",
"type": "conference_item",
"title": "Numerical Simulations of Natural and Actuated Flow over a 3-D, Low-Aspect-Ratio Airfoil",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Numerical simulations of the unsteady flow over a low-aspect-ratio, low Reynolds number semi-circular planform wing are performed using Lattice Boltzmann method. The simulations exactly match the flow conditions and the detailed geometry from previous wind-tunnel experiments, including the flow actuators installed internally along the leading edge of the wing. To reproduce the pulsed-blowing actuation used in the experiment, a single pulsed square wave forcing is imposed in the simulations as a mass flow boundary condition in the actuators. Three angles of attack, with the active flow control both on and off, are investigated. For both mean and unsteady lift and drag, the numerical simulations show good agreement with the experiments. In particular, the transient increase in lift after the forcing is turned off is well captured in the simulations. Both PIV measurements and transient numerical results indicate that this behavior is associated with the advectionof large vortical structures generated by the flow actuation at the leading edge.",
"doi": "10.2514/6.2010-4713",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2010-06"
},
{
"id": "authors:2y36w-k9688",
"collection": "authors",
"collection_id": "2y36w-k9688",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102317853",
"type": "conference_item",
"title": "An Integrated RANS-PSE-Wave Packet Tool for the Prediction of Subsonic and Supersonic Jet Noise",
"author": [
{
"family_name": "Ladeinde",
"given_name": "Foluso",
"clpid": "Ladeinde-F"
},
{
"family_name": "Alabi",
"given_name": "Ken",
"clpid": "Alabi-Ken"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Gudmundsson",
"given_name": "Kristjan",
"clpid": "Gudmundsson-K"
},
{
"family_name": "Schlinker",
"given_name": "Robert H.",
"clpid": "Schlinker-R-H"
},
{
"family_name": "Reba",
"given_name": "Ramons A.",
"clpid": "Reba-R-A"
}
],
"abstract": "Few engineering tools are suitable for predicting supersonic jet noise, and the development of engine exhaust noise reduction technology for tactical aircraft continues to rely heavily on laboratory scale parametric testing. Aside from intuition and experience with the generally subtle issues involved in low-noise design, there is currently no way to rapidly and cheaply assess whether proposed designs will be effective, and no way to determine whether such designs are optimal. Arguably, this gap in jet noise modeling capability is an impediment toward achieving significant noise reduction for tactical aircraft. The objective of the on-going research program presented in this paper is to develop and demonstrate innovative, highly-efficient computational methodologies for simultaneous nozzle acoustic and aerodynamic design applicable to subsonic and supersonic jet exhaust noise reduction in tactical aircraft. The approach comprises of three major elements: (1) Reynolds-averaged NavierStokes (RANS)-CFD for computing the jet turbulent mean flow, (2) pressure wave packet-based methods for predicting near-field sound generation from the largest scales, based on the Linear Parabolized Stability Equations (LPSE) and the aforementioned RANS solutions, and (3) a method based on the solution of the linear wave equation for determining the acoustic radiation field from the LPSE solution. While these three procedures have received significant attention in the literature, their integration into a single tool for far-field noise prediction has not. To assess the accuracy and robustness of the simulation tool, experimental data has been acquired with near field array directed at detecting changes in the organized turbulence scale structure to link cause (nozzle geometry) and effect (near field and far field noise changes). Both ideally- and non-ideally expanded conditions are being investigated. Forward flight effects have also been measured using an open jet acoustic wind tunnel (at United Technologies Research Center) to evaluate the noise dependence on different operating conditions. The development and preliminary validation of the integrated tool is presented in this paper, with a focus on individual components and their translation into a common format for integration.",
"doi": "10.2514/6.2010-4021",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2010-06"
},
{
"id": "authors:q1njr-bft11",
"collection": "authors",
"collection_id": "q1njr-bft11",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100623-152555163",
"type": "article",
"title": "Compressible Large-Eddy Simulation of Separation Control on a Wall-Mounted Hump",
"author": [
{
"family_name": "Franck",
"given_name": "Jennifer A.",
"clpid": "Franck-J-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Compressible large-eddy simulations of turbulent flow over a wall-mounted hump with active flow control are\nperformed and compared with previous experiments. The flow is characterized by the unsteady separation before the\nsteep trailing edge, which naturally reattaches downstream of the hump to form an unsteady turbulent separation\nbubble. The low Mach number large-eddy simulation demonstrated a good prediction of surface pressure coefficient,\nseparation-bubble length, and velocity profiles compared with experiments. The effect of compressibility on the\nbaseline flow is documented and analyzed and is found to increase the separation-bubble size, due to a reduced\ngrowth rate. Control is applied just before the natural separation point via steady suction and zero-net-mass-flux\noscillatory forcing, and steady suction is shown to be more effective in decreasing the size of the separation bubble and\npressure drag for the control parameters investigated. Controlled flow at a compressible subsonic Mach number is\napplied, and found to be slightly less effective than the same control parameters at low Mach numbers.",
"doi": "10.2514/1.44756",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2010-06",
"series_number": "6",
"volume": "48",
"issue": "6",
"pages": "1098-1107"
},
{
"id": "authors:0aycy-d4x55",
"collection": "authors",
"collection_id": "0aycy-d4x55",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190215-114821703",
"type": "book_section",
"title": "Unstructured Large Eddy Simulation Technology for Prediction and Control of Jet Noise",
"book_title": "Proceedings of the ASME Turbo Expo 2010",
"author": [
{
"family_name": "Khalighi",
"given_name": "Yaser",
"clpid": "Khalighi-Y"
},
{
"family_name": "Ham",
"given_name": "Frank",
"clpid": "Ham-F"
},
{
"family_name": "Moin",
"given_name": "Parviz",
"orcid": "0000-0002-0491-7065",
"clpid": "Moin-Parviz"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
},
{
"family_name": "Schlinker",
"given_name": "Robert H.",
"clpid": "Schlinker-R-H"
},
{
"family_name": "Reba",
"given_name": "Ramons A.",
"clpid": "Reba-R-A"
},
{
"family_name": "Simonich",
"given_name": "John",
"clpid": "Simonich-J-C"
}
],
"abstract": "Development of concepts for reduction of jet noise has relied heavily on expensive experimental testing of various nozzle designs. For example, the design of nozzle serrations (chevron) and internal mixer/ejector nozzles have relied largely on laboratory and full-scale testing. Without a deeper understanding of the sources of high-speed jet noise it is very difficult to effectively design configurations that reduce the noise and maintain other performance metrics such as nozzle thrust. In addition, the high complexity of the flow limits the success of a parametric black-box optimization.",
"doi": "10.1115/GT2010-22306",
"isbn": "978-0-7918-4396-3",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "2010-06",
"pages": "57-70"
},
{
"id": "authors:k7ftv-qy132",
"collection": "authors",
"collection_id": "k7ftv-qy132",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100810-142241271",
"type": "article",
"title": "Wave-packet models for large-scale mixing noise",
"author": [
{
"family_name": "Reba",
"given_name": "Ramons",
"clpid": "Reba-R"
},
{
"family_name": "Narayanan",
"given_name": "Satish",
"clpid": "Narayanan-S"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "A wave-packet Ansatz is used to model jet noise generation by large-scale turbulence. In this approach, an equivalent source is defined based on the two-point space-time correlation of hydrodynamic pressure on a conical surface surrounding the jet plume. The surface is sufficiently near the turbulent flow region to be dominated by non-propagating hydrodynamic signatures of large-scale turbulent structures, yet sufficiently far that linear behavior can be assumed in extending the near-field pressure to the acoustic field. In the present study, a 78-microphone array was used to measure hydrodynamic pressure on the conical surface in order to identify parameters for the model and to validate the approach. Six microphones were distributed in the azimuthal direction at each of 13 axial locations spanning the first 8 jet diameters, allowing decomposition of azimuthal modes m = 0 and m = 1. We show that a source model based on a Gaussian correlation function provides a consistently good representation of the noise source attributed to large-scale structures. The results provide evidence that large-scale wave-like structures, known to dominate aft radiation at supersonic phase speeds, are also relevant at subsonic speeds.",
"doi": "10.1260/1475-472X.9.4-5.533",
"issn": "1475-472X",
"publisher": "Multi-Science Publishing",
"publication": "International Journal of Aeroacoustics",
"publication_date": "2010-06",
"series_number": "4-5",
"volume": "9",
"issue": "4-5",
"pages": "533-557"
},
{
"id": "authors:ynx4y-x5694",
"collection": "authors",
"collection_id": "ynx4y-x5694",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170408-171700963",
"type": "article",
"title": "Computational Modeling and Experiments of Natural Convection for a Titan Montgolfiere",
"author": [
{
"family_name": "Samanta",
"given_name": "Arnab",
"clpid": "Samanta-A"
},
{
"family_name": "Appel\u00f6",
"given_name": "Daniel",
"clpid": "Appel\u00f6-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Nott",
"given_name": "Julian",
"clpid": "Nott-J"
},
{
"family_name": "Hall",
"given_name": "Jeffrey",
"clpid": "Hall-J"
}
],
"abstract": "Computational models are developed to predict the natural convection heat transfer and buoyancy for a Montgolfiere under conditions relevant to the Titan atmosphere. Idealized single- and double-walled balloon geometries are simulated using algorithms suitable for both laminar and (averaged) turbulent convection. Steady-state performance results are compared with existing heat transfer coefficient correlations. The laminar results, in particular, are used to test the validity of the correlations in the absence of uncertainties associated with turbulence modeling. Some discrepancies are observed, which appear to be primarily associated with temperature nonuniformity on the balloon surface. The predicted buoyancy for both the single- and double-walled balloons in the turbulent convection regime, predicted with standard two-equation turbulence models, showed trends similar to those with the empirical correlations. There was also good agreement with recently conducted experiments in a cryogenic facility designed to simulate the Titan atmosphere.",
"doi": "10.2514/1.45854",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2010-05",
"series_number": "5",
"volume": "48",
"issue": "5",
"pages": "1007-1016"
},
{
"id": "authors:fmcs4-rhk52",
"collection": "authors",
"collection_id": "fmcs4-rhk52",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100520-150834651",
"type": "article",
"title": "The leading-edge vortex and quasisteady vortex shedding on an accelerating plate",
"author": [
{
"family_name": "Chen",
"given_name": "Kevin K.",
"clpid": "Chen-Kevin-K"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
}
],
"abstract": "A computational inquiry focuses on leading-edge vortex (LEV) growth and shedding during acceleration of a two-dimensional flat plate at a fixed 10\u00b0\u201360\u00b0 angle of attack and low Reynolds number. The plate accelerates from rest with a velocity given by a power of time ranging from 0 to 5. During the initial LEV growth, subtraction of the added mass lift from the computed lift reveals an LEV-induced lift augmentation evident across all powers and angles of attack. For the range of Reynolds numbers considered, a universal time scale exists for the peak when \u03b1 \u2265 30\u00b0, with augmentation lasting about four to five chord lengths of translation. This time scale matches well with the half-stroke of a flying insect. An oscillating pattern of leading- and trailing-edge vortex shedding follows the shedding of the initial LEV. The nondimensional frequency of shedding and lift coefficient minima and maxima closely match their values in the absence of acceleration. These observations support a quasisteady theory of vortex shedding, where dynamics are determined primarily by velocity and not acceleration. Finally, the nondimensional vortex formation time is found to be a function of the Reynolds number, but only weakly when the Reynolds number is high.",
"doi": "10.1063/1.3327282",
"issn": "1070-6631",
"publisher": "American Institute of Physics",
"publication": "Physics of Fluids",
"publication_date": "2010-03",
"series_number": "3",
"volume": "22",
"issue": "3",
"pages": "Art. No. 033601"
},
{
"id": "authors:t4v19-d0h03",
"collection": "authors",
"collection_id": "t4v19-d0h03",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-125448163",
"type": "book_section",
"title": "Towards Prediction and Control of Large Scale Turbulent Structure Supersonic Jet Noise",
"book_title": "Proceedings of the ASME Turbo Expo 2009",
"author": [
{
"family_name": "Schlinker",
"given_name": "Robert H.",
"clpid": "Schlinker-R-H"
},
{
"family_name": "Reba",
"given_name": "Ramons A.",
"clpid": "Reba-R-A"
},
{
"family_name": "Simonich",
"given_name": "John C.",
"clpid": "Simonich-J-C"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Gudmundsson",
"given_name": "Kristjan",
"clpid": "Gudmundsson-K"
},
{
"family_name": "Ladeinde",
"given_name": "Foluso",
"clpid": "Ladeinde-F"
}
],
"abstract": "In this paper, we report on progress towards developing physics-based models of sound generation by large-scale turbulent structures in supersonic jet shear layers generally accepted to be the source of aft-angle noise. Aside from obtaining better engineering prediction schemes, the development and optimization of long term jet noise reduction strategies based on controlling instability wave generated large-scale turbulence structures in the shear layer can be more successful if based on predictive flow-noise models, rather than on build and test approaches alone. Such models, if successful, may also provide a path by which laboratory scale demonstrations can be more reliably translated to engine scale. Results show that the noise radiated by large-scale structures in turbulent jet shear layers may be modeled using a RANS based PSE method and projected to the far-field using a Kirchhoff surface approach. A key enabler in this procedure is the development of near-field microphone arrays capable of providing the pressure statistics needed to validate the instability wave models. Our framework provides, for the first time, a deterministic model that will allow understanding and predicting noise radiated by large-scale turbulence.",
"doi": "10.1115/gt2009-60300",
"isbn": "978-0-7918-4882-1",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "2010-02-23",
"pages": "217-230"
},
{
"id": "authors:knhq1-chv66",
"collection": "authors",
"collection_id": "knhq1-chv66",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100308-144328976",
"type": "article",
"title": "Acoustic Properties of Porous Coatings for Hypersonic Boundary-Layer Control",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Fedorov",
"given_name": "Alexander V.",
"clpid": "Fedorov-A-V"
}
],
"abstract": "Numerical simulations are performed to investigate the interaction of acoustic waves with an array of equally\nspaced two-dimensional microcavities on an otherwise flat plate without external boundary-layer flow. This acoustic\nscattering problem is important in the design of ultrasonic absorptive coatings for hypersonic laminar flow control.\nThe reflection coefficient, characterizing the ratio of the reflected wave amplitude to the incident wave amplitude, is\ncomputed as a function of the acoustic wave frequency and angle of incidence, for coatings of different porosities, at\nvarious acoustic Reynolds numbers relevant to hypersonic flight. Overall, the numerical results validate predictions\nfrom existing theoretical modeling. In general, the amplitude of the reflection coefficient has local minima at some\nspecific frequencies. A simple model to predict these frequencies is presented. The simulations also highlight the\npresence of resonant acoustic modes caused by coupling of small-scale scattered waves near the coating surface.\nFinally, the cavity depth and the porosity are identified as the most important parameters for coating design.\nGuidelines for the choice of these parameters are suggested.",
"doi": "10.2514/1.40811",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2010-02",
"series_number": "2",
"volume": "48",
"issue": "2",
"pages": "267-274"
},
{
"id": "authors:m7ghj-7ct15",
"collection": "authors",
"collection_id": "m7ghj-7ct15",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320131",
"type": "conference_item",
"title": "Feedback Control of High-Lift State for A Low-Aspect-Ratio Wing",
"author": [
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
},
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The objective of this study is to employ feedback control to maximize time-average lift on a low-aspect-ratio wing by directly modifying the three-dimensional dynamics of the wake vortices. Flow control around such wing at post-stall angles of attack is numerically investigated at a low Reynolds number of 300 with blowing along the trailing edge. Motivated by the existence of time-periodic high-lift states under open-loop control with periodic excitation, the extremum seeking algorithm is considered for designing feedback control to lock the flow onto such high-lift states. Preliminary results are presented where the close-loop control is able to seek the optimal actuation frequency and yield high lift.",
"doi": "10.2514/6.2010-357",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2010-01"
},
{
"id": "authors:06ncw-yc540",
"collection": "authors",
"collection_id": "06ncw-yc540",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102319753",
"type": "conference_item",
"title": "Closed-Loop Control of a Wing in an Unsteady Flow",
"author": [
{
"family_name": "Williams",
"given_name": "David",
"clpid": "Williams-D"
},
{
"family_name": "Kerstens",
"given_name": "Wesley",
"clpid": "Kerstens-W"
},
{
"family_name": "Buntain",
"given_name": "Seth",
"clpid": "Buntain-S"
},
{
"family_name": "Quach",
"given_name": "Vien",
"clpid": "Quach-V"
},
{
"family_name": "Pfeiffer",
"given_name": "Jens",
"clpid": "Pfeiffer-J"
},
{
"family_name": "King",
"given_name": "Rudibert",
"clpid": "King-R"
},
{
"family_name": "Tadmor",
"given_name": "Gilead",
"clpid": "Tadmor-G"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The lift response of the separated flow over a wing to different actuator input disturbances is used to obtain linear models useful for closed-loop control design. The wing has a small aspect ratio, a semi-circular planform, and is fully stalled at a 20\u00b0 angle of attack. Individual pulse-like disturbances and step-input disturbances with randomized frequency were inputs to the actuator, and the lift coefficient increments were output signals. The \"prediction error method\" system identification technique was used to obtain two linear models of the separated flow. A 4th order model reproduced the non-minimum phase behavior of the pulse input, but did not work well for control purposes. The second model identified was limited to first order. The first order model proved to be useful for designing a proportional-integral feedback controller capable of suppressing lift oscillations in unsteady flows. Good suppression of lift oscillations was observed in the experiment after a step change in wind tunnel flow speed occurred. When the control system was tested with a randomized freestream velocity, it reduced the root-mean-square lift oscillation by 50 percent relative to the uncontrolled case.",
"doi": "10.2514/6.2010-358",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2010-01"
},
{
"id": "authors:swhx3-hqn46",
"collection": "authors",
"collection_id": "swhx3-hqn46",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102317714",
"type": "book_section",
"title": "Unsteady Lift Suppression with a Robust Closed Loop Controller",
"book_title": "Active Flow Control II",
"author": [
{
"family_name": "Williams",
"given_name": "David",
"clpid": "Williams-D"
},
{
"family_name": "Kerstens",
"given_name": "Wesley",
"clpid": "Kerstens-W"
},
{
"family_name": "Pfeiffer",
"given_name": "Jens",
"clpid": "Pfeiffer-J"
},
{
"family_name": "King",
"given_name": "Rudibert",
"clpid": "King-R"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "King",
"given_name": "Rudibert",
"clpid": "King-R"
}
],
"abstract": "The ability to control lift in unsteady flows using active flow control is examined experimentally with a three-dimensional, low-aspect-ratio wing and pulsed-blowing actuators as the test article. An unsteady flow wind tunnel is used to generate step-like and harmonic oscillations in flow speed and the corresponding fluctuating lift force on the wing. A 'black box' model of the wing response to actuation is obtained using conventional system identification techniques. A robust H\u2009_\u221e\u2009 controller is designed with a mixed sensitivity loop-shaping technique, whose objective was to maintain a constant lift in the unsteady flow. The controller is shown to be capable of significant reductions in lift fluctuations given step, harmonic and random input disturbance conditions.",
"doi": "10.1007/978-3-642-11735-0_2",
"isbn": "9783642117343",
"publisher": "Springer",
"place_of_publication": "Berlin, Germany",
"publication_date": "2010",
"pages": "19-30"
},
{
"id": "authors:h606f-x2q76",
"collection": "authors",
"collection_id": "h606f-x2q76",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-083422063",
"type": "book_section",
"title": "Lock-On to a High-Lift State with Oscillatory Forcing in a Three-Dimensional Wake Flow",
"book_title": "Active Flow Control II",
"author": [
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
},
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "King",
"given_name": "Rudibert",
"clpid": "King-R"
}
],
"abstract": "Flow control is applied to a three-dimensional post-stall flow around a rectangular low-aspect-ratio wing. Steady actuation is used to examine effective flow control setups that modify the vortex dynamics in the wake and achieve increase in lift. For one of the setups, oscillatory forcing is then used to examine the influence of actuation frequency. It is found that sinusoidal actuation requires less momentum to the flow field to achieve lift increase compared to steady momentum injection. There are two observed ranges of forcing frequency at which the flow locks onto period-one and period-two high-lift states. Discussions of the ongoing work on stabilizing separated flow about these periodic high-lift states are offered.",
"doi": "10.1007/978-3-642-11735-0_6",
"isbn": "978-3-642-11734-3",
"publisher": "Springer",
"place_of_publication": "Berlin",
"publication_date": "2010",
"pages": "81-93"
},
{
"id": "authors:qe3p9-faa39",
"collection": "authors",
"collection_id": "qe3p9-faa39",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110321-092415409",
"type": "article",
"title": "Development of Arbitrary-Order Hermite Methods for Simulation and Analysis of Turbulent Jet Noise",
"author": [
{
"family_name": "Appel\u00f6",
"given_name": "Daniel",
"clpid": "Appel\u00f6-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Hagstrom",
"given_name": "Thomas",
"clpid": "Hagstrom-T"
},
{
"family_name": "Inkman",
"given_name": "Matthew",
"clpid": "Inkman-M"
}
],
"abstract": "In this short note a brief description of Hermite methods is given. Previous and ongoing development of arbitrary\norder Hermite methods for the simulation of turbulent jets is also presented. In addition we outline how Hermite\nmethods can be hybridized with discontinuous Galerkin methods to handle boundary conditions in a straightforward\nway.",
"doi": "10.1016/j.proeng.2010.09.003",
"issn": "1877-7058",
"publisher": "Elsevier",
"publication": "Procedia Engineering",
"publication_date": "2010",
"volume": "6",
"pages": "19-27"
},
{
"id": "authors:7m4qg-zc506",
"collection": "authors",
"collection_id": "7m4qg-zc506",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110418-093737292",
"type": "book_section",
"title": "Optimized Waveforms for Feedback Control of Vortex Shedding",
"book_title": "Active flow control II",
"author": [
{
"family_name": "Joe",
"given_name": "Won Tae",
"clpid": "Joe-Won-Tae"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "MacMynowski",
"given_name": "Douglas G.",
"orcid": "0000-0003-1987-9417",
"clpid": "MacMartin-D-G"
}
],
"contributor": [
{
"family_name": "King",
"given_name": "Rudibert",
"clpid": "King-R"
}
],
"abstract": "Optimal control theory is combined with the numerical simulation of an incompressible viscous flow to control vortex shedding in order to maximize lift. A two-dimensional flat plate model is considered at a high angle of attack and a Reynolds number of 300. Actuation is provided by unsteady mass injection near the trailing edge and is modeled by a compact body force. The adjoint of the linearized perturbed equations is solved backwards in time to obtain the gradient of the lift to changes in actuation (the jet velocity), and this information is used to iteratively improve the controls. The optimized control waveform is nearly periodic and locked to vortex shedding. We compare the results with sinusoidal open- and closed-loop control and observe that the optimized control is able to achieve higher lift than the sinusoidal forcing with more than 50% lower momentum coefficients. The optimized waveform is also implemented in a simple closed-loop controller where the control signal is shifted or deformed periodically to adjust to the (instantaneous) frequency of the lift fluctuations. The feedback utilizes a narrowband filter and an Extended Kalman Filter to robustly estimate the phase of vortex shedding and achieve phase-locked, high lift flow states.",
"doi": "10.1007/978-3-642-11735-0_25",
"isbn": "978-3-642-11734-3",
"publisher": "Springer",
"place_of_publication": "Berlin",
"publication_date": "2010",
"pages": "391-404"
},
{
"id": "authors:7x47c-dnj36",
"collection": "authors",
"collection_id": "7x47c-dnj36",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20110318-153515340",
"type": "article",
"title": "Parabolized stability equation models of large-scale jet mixing noise",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Samanta",
"given_name": "Arnab",
"clpid": "Samanta-Arnab"
},
{
"family_name": "Gudmundsson",
"given_name": "Kristjan",
"clpid": "Gudmundsson-K"
}
],
"contributor": [
{
"family_name": "Astley",
"given_name": "R. J.",
"clpid": "Astley-R-J"
},
{
"family_name": "Gabard",
"given_name": "G.",
"clpid": "Gabard-G"
}
],
"abstract": "We report on the development of parabolized stability equation models to predict the evolution of low frequencies, large-scale wavepacket\n structures in turbulent jets and their radiated sound. We consider\n computations and data corresponding to high subsonic and supersonic\n jets from circular nozzles. Previous methods are extended to consider\n nonlinear interactions amongst the waves and use a Kirchhoff-surface\n type approach to project the near-field wavepacket amplitudes to the\n far-field. Linear PSE, whose initial conditions are chosen to provide\n an overall amplitude reference, show excellent agreement for the\n wavepacket amplitudes and phases with microphone array data just\n outside the jet shear layers, especially when the microphone data are\n processed to filter out contributions from uncorrelated fluctuations.\n Far-field sound predictions based on the linear PSE are also in\n reasonable agreement with far-field data. In order to investigate\n nonlinearity, we use an LES database to evaluate initial conditions for\n the PSE modes, and then compare their later evolution along the jet.\n Preliminary cases show some sensitivity to the initial amplitudes and\n their phases, and that nonlinear effects may be important in predicting\n the far-field sound based on the initial (near-nozzle) spectrum of\n disturbances.",
"doi": "10.1016/j.proeng.2010.09.008",
"issn": "1877-7058",
"publisher": "Elsevier",
"publication": "Procedia Engineering",
"publication_date": "2010",
"volume": "6",
"pages": "64-73"
},
{
"id": "authors:rtdx6-f4z42",
"collection": "authors",
"collection_id": "rtdx6-f4z42",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091223-094524380",
"type": "article",
"title": "Lift Response of a Stalled Wing to Pulsatile Disturbances",
"author": [
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
},
{
"family_name": "Tadmor",
"given_name": "Gilead",
"clpid": "Tadmor-G"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Kerstens",
"given_name": "Wesley",
"clpid": "Kerstens-W"
},
{
"family_name": "Quach",
"given_name": "Vien",
"clpid": "Quach-V"
},
{
"family_name": "Buntain",
"given_name": "Seth",
"clpid": "Buntain-S"
}
],
"abstract": "The transient lift response of a low-Reynolds-number wing subjected to small amplitude pulsatile disturbances is investigated. The wing has a small aspect ratio and a semicircular planform, and it is fully stalled at a 20 deg angle of attack. Microvalve actuators distributed along the leading edge of the wing produce the transient disturbance. It is shown that the lift response to a single pulse increases with increasing actuator supply pressure and that the lift response curves are similar to each other when scaled by the total impulse. Furthermore, for fixed actuator supply pressure, the amplitude and total impulse of the transient lift response curve increases with increasing external flow speed. In this case, the lift response curves are similar when scaled by the dynamic pressure. The lift response to a single pulse can be treated as a filter kernel, and it can be used to predict the lift time history for the arbitrary actuator input signals. The kernel is similar in shape to transient measurements obtained by other investigators on two-dimensional wings and flaps. Comparisons between the model predictions and the experiments using multiple pulse inputs and square-wave modulated input signals at low frequencies are presented.",
"doi": "10.2514/1.45407",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2009-12",
"series_number": "12",
"volume": "47",
"issue": "12",
"pages": "3031-3037"
},
{
"id": "authors:jcp2f-xng50",
"collection": "authors",
"collection_id": "jcp2f-xng50",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090916-093310681",
"type": "article",
"title": "Improvement of acoustic theory of ultrasonic waves in dilute bubbly liquids",
"author": [
{
"family_name": "Ando",
"given_name": "Keita",
"clpid": "Ando-Keita"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "Christopher E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "The theory of the acoustics of dilute bubbly liquids is reviewed, and the dispersion relation is modified by including the effect of liquid compressibility on the natural frequency of the bubbles. The modified theory is shown to more accurately predict the trend in measured attenuation of ultrasonic waves. The model limitations associated with such high-frequency waves are discussed.",
"doi": "10.1121/1.3182858",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2009-07-27",
"series_number": "3",
"volume": "126",
"issue": "3",
"pages": "EL69"
},
{
"id": "authors:vzca5-fha04",
"collection": "authors",
"collection_id": "vzca5-fha04",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090904-093528277",
"type": "article",
"title": "Numerical simulations of non-spherical bubble collapse",
"author": [
{
"family_name": "Johnsen",
"given_name": "Eric",
"clpid": "Johnsen-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "A high-order accurate shock- and interface-capturing scheme is used to simulate the collapse of a gas bubble in water. In order to better understand the damage caused by collapsing bubbles, the dynamics of the shock-induced and Rayleigh collapse of a bubble near a planar rigid surface and in a free field are analysed. Collapse times, bubble displacements, interfacial velocities and surface pressures are quantified as a function of the pressure ratio driving the collapse and of the initial bubble stand-off distance from the wall; these quantities are compared to the available theory and experiments and show good agreement with the data for both the bubble dynamics and the propagation of the shock emitted upon the collapse. Non-spherical collapse involves the formation of a re-entrant jet directed towards the wall or in the direction of propagation of the incoming shock. In shock-induced collapse, very high jet velocities can be achieved, and the finite time for shock propagation through the bubble may be non-negligible compared to the collapse time for the pressure ratios of interest. Several types of shock waves are generated during the collapse, including precursor and water-hammer shocks that arise from the re-entrant jet formation and its impact upon the distal side of the bubble, respectively. The water-hammer shock can generate very high pressures on the wall, far exceeding those from the incident shock. The potential damage to the neighbouring surface is quantified by measuring the wall pressure. The range of stand-off distances and the surface area for which amplification of the incident shock due to bubble collapse occurs is determined.",
"doi": "10.1017/S0022112009006351",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2009-06-25",
"volume": "629",
"pages": "231-262"
},
{
"id": "authors:27fx2-jcb90",
"collection": "authors",
"collection_id": "27fx2-jcb90",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090721-120325880",
"type": "article",
"title": "A high-order super-grid-scale absorbing layer and its application to linear hyperbolic systems",
"author": [
{
"family_name": "Appel\u00f6",
"given_name": "Daniel",
"clpid": "Appel\u00f6-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We continue the development of the super-grid-scale model initiated in [T. Colonius, H. Ran, A super-grid-scale model for simulating compressible flow on unbounded domains, J. Comput. Phys. 182 (1) (2002) 191\u2013212] and consider its application to linear hyperbolic systems. The super-grid-scale model consists of two parts: reduction of an unbounded to a bounded domain by a smooth coordinate transformation and a damping of those scales. For linear problems the super-grid scales are analogous to spurious numerical waves. We damp these waves by high-order undivided differences. We compute reflection coefficients for different orders of the damping and find that significant improvements are obtained when high-order damping is used.\nIn numerical experiments with Maxwell's equations, we show that when the damping is of high order, the error from the boundary condition converges at the order of the interior scheme. We also demonstrate that the new method achieves perfectly matched layer-like accuracy.\nWhen applied to linear hyperbolic systems the stability of the super-grid-scale method follows from its construction. This makes our method particularly suitable for problems for which perfectly matched layers are unstable. We present results for two such problems: elastic waves in anisotropic media and isotropic elastic waves in wave guides with traction-free surfaces.",
"doi": "10.1016/j.jcp.2009.02.030",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2009-06-20",
"series_number": "11",
"volume": "228",
"issue": "11",
"pages": "4200-4217"
},
{
"id": "authors:se92k-k1z30",
"collection": "authors",
"collection_id": "se92k-k1z30",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102318383",
"type": "conference_item",
"title": "Optimized Control of Vortex Shedding From an Inclined Flat Plate",
"author": [
{
"family_name": "Joe",
"given_name": "Won Tae",
"clpid": "Joe-Won-Tae"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "MacMynowski",
"given_name": "Douglas G.",
"orcid": "0000-0003-1987-9417",
"clpid": "MacMartin-D-G"
}
],
"abstract": "Optimal control theory is combined with the numerical simulation of an incompressible viscous flow to control vortex shedding in order to maximize lift. A two-dimensional flat plate model is considered at a high angle of attack and a Reynolds number of 300. Actuation is provided by unsteady mass injection near the trailing edge and is modeled by a compact body force. The adjoint of the linearized perturbed equations is solved backwards in time to obtain the gradient of the lift to changes in actuation (the jet velocity), and this information is used to iteratively improve the controls. The optimized control waveform is nearly periodic and locked to vortex shedding. We investigate how features of the optimized waveform modify the vortex shedding and lead to higher lift, and compare the results with sinusoidal open- and closed-loop control from a previous study. In the cases investigated, the optimized control is able to achieve higher average lift than the sinusoidal forcing with lower momentum coefficients. In order to obtain a practically implementable control scheme, the optimized waveform is also implemented in a simple closed-loop controller where the control signal is shifted or deformed periodically to adjust to the (instantaneous) frequency of the lift fluctuations. The feedback utilizes a narrowband filter and an Extended Kalman Filter to robustly estimate the phase of vortex shedding and achieve phase-locked, high lift flow states. Finally, the sensitivity of the flow to the phase shift and other features of the optimized waveform are examined.",
"doi": "10.2514/6.2009-4027",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2009-06"
},
{
"id": "authors:gbcy2-76j32",
"collection": "authors",
"collection_id": "gbcy2-76j32",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102318572",
"type": "conference_item",
"title": "Oscillatory Control and the Effects of Actuation Frequency on a Wall-Mounted Hump",
"author": [
{
"family_name": "Franck",
"given_name": "Jennifer",
"clpid": "Franck-J-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "A large eddy simulation (LES) is used to explore the effects of high frequency actuation on a wall-mounted hump geometry. Low frequency forcing at F^+ ~ O(1) has been shown to increase entrainment through regular shedding of large-scale structures. Using a LES technique previously validated on the baseline and controlled flow over the wall-mounted hump geometry, the effectiveness of high frequency actuation is explored and compared with previous investigations. It is found that the high frequency actuation does not produce distinct vortical structures at the actuation frequency. The resulting mean flow is relatively unaltered by the application of high frequency actuation, although the local flow surrounding the actuation location is slightly modified.",
"doi": "10.2514/6.2009-4019",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2009-06"
},
{
"id": "authors:1bd7n-63c93",
"collection": "authors",
"collection_id": "1bd7n-63c93",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102319429",
"type": "conference_item",
"title": "Alternate Designs of Ultrasonic Absorptive Coatings for Hypersonic Boundary Layer Control",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Inkman",
"given_name": "Matthew",
"clpid": "Inkman-M"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Fedorov",
"given_name": "Alexander V.",
"clpid": "Fedorov-A-V"
}
],
"abstract": "Numerical simulations of the linear and nonlinear two-dimensional Navier-Stokes equations are used to parametrically investigate hypersonic boundary layers over ultrasonic absorptive coatings consisting of a uniform array of rectangular pores (slots) with a range of porosities and pore aspect ratios. Based on our previous work, we employ a temporally evolving approximation appropriate to slowly-growing second-mode instabilities. We consider coatings operating in attenuative regimes where the pores are relatively deep and acoustic waves and second mode instabilities are attenuated by viscous effects inside the pores, as well as cancellation/reinforcement regimes with alternating regions of local minima and maxima of the coating acoustic absorption, depending on the frequency of the acoustic waves. The focus is on reinforcement cases which represent a worst case scenario (minimal second-mode damping). For all but one of the cases considered, the linear simulations confirm the results of linear instability theory that employs an approximate porous-wall boundary condition. A particular case with a relatively shallow cavities and very high porosity showed the existence of a shorter wavelength instability that is not predicted by theory. Finally, nonlinear simulations of the same cases led to the same conclusions as linear analysis; in particular, we did not observe any \"tripping\" of the boundary layer by small scale disturbances associated with individual pores.",
"doi": "10.2514/6.2009-4217",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2009-06"
},
{
"id": "authors:mjba7-nzm77",
"collection": "authors",
"collection_id": "mjba7-nzm77",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100819-150529622",
"type": "article",
"title": "Numerical simulation of the sound radiated by a turbulent vortex ring",
"author": [
{
"family_name": "Ran",
"given_name": "Hongyu",
"clpid": "Ran-Hongyu"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The acoustic field radiated by a turbulent vortex ring is studied. Direct Numerical Simulations\n(ONS) of the fully compressible, three-dimensional Navier-Stokes equations are used to generate\nan axisymmetric vortex ring to which 3D stochastic disturbances are added. The disturbances\ncause instability and turbulent transition of the vortex ring. Detailed information about temporal\nevolution of sound pressure level, spectrum and directivity associated with modes of oscillation\nand their turbulent breakdown are investigated. The peak frequency agrees well with experiments.\nand the modal directivities agree well with predictions of vortex sound theory. Based on the self-similar\ndecay of the turbulent near field, the self-similar decay of the sound field is investigated.\nWe also explore the connections with jet noise by modeling the jet as a de-correlated train of\nvortex rings.",
"issn": "1475-472X",
"publisher": "Multi-Science Publishing",
"publication": "International Journal of Aeroacoustics",
"publication_date": "2009-06",
"series_number": "4",
"volume": "8",
"issue": "4",
"pages": "317-336"
},
{
"id": "authors:phrw0-8sg81",
"collection": "authors",
"collection_id": "phrw0-8sg81",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100819-150126006",
"type": "article",
"title": "Turbulence and sound-field POD analysis of a turbulent jet",
"author": [
{
"family_name": "Freund",
"given_name": "J. B.",
"clpid": "Freund-J-B"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "A Proper Orthogonal Decomposition (POD) is constructed for a Mach 0.9 turbulent jet using a\nwell-validated direct numerical simulation database. Norms are defined based on near-field\nvolume integrals of pressure, turbulence kinetic energy, streamwisc velocity, and total enthalpy,\ntwo-dimensional integrals of streamswise velocity (to match experimental measurements), and\nfar-field integrals of pressure over a sphere. We find substantially different POD modes for the\ndifferent norms, and their efficiency at representing the full data is strongly dependent upon the\nnorm and specifically which data we attempt to represent. To reproduce near-field turbulence\nstatistics requires relatively few modes computed by a kinetic energy or pressure norm. However.\na large number of the POD modes computed using a near-field norm are required to represent the\nsound field. The dominant near-field POD modes computed with either the near-field pressure\nnorm or the sound field norm have the structure of wave packets.",
"issn": "1475-472X",
"publisher": "Multi-Science Publishing",
"publication": "International Journal of Aeroacoustics",
"publication_date": "2009-06",
"series_number": "4",
"volume": "8",
"issue": "4",
"pages": "337-354"
},
{
"id": "authors:3bc9z-pvj11",
"collection": "authors",
"collection_id": "3bc9z-pvj11",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102318476",
"type": "conference_item",
"title": "Parabolized Stability Equation Models for Turbulent Jets and Their Radiated Sound",
"author": [
{
"family_name": "Gudmundsson",
"given_name": "Kristjan",
"clpid": "Gudmundsson-K"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "In this paper we present several refinements to a wave-packet model of sound generation from large-scale turbulence. We examine heated and unheated jets at Mach numbers of 0.5 and 0.9. Pressure fluctuations associated with large-scale structures are modeled with the Parabolized Stability Equations (PSE) for linear disturbances to the turbulent mean-flow. We show that PSE provides better agreement with near-field microphone-array data at low frequencies than previous models based on linear stability theory. We examine the extent to which microphone data is contaminated by fluctuations uncorrelated with largescale structures. By filtering out the uncorrelated fluctuations, via the proper orthogonal decomposition (POD), better agreement between data and theory is obtained.",
"doi": "10.2514/6.2009-3380",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2009-05"
},
{
"id": "authors:q9w9t-kra38",
"collection": "authors",
"collection_id": "q9w9t-kra38",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102317615",
"type": "conference_item",
"title": "Computational Modeling and Experiments of Natural Convection for a Titan Montgolfiere",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Appel\u00f6",
"given_name": "Daniel",
"clpid": "Appel\u00f6-D"
},
{
"family_name": "Nott",
"given_name": "Julian",
"clpid": "Nott-J"
},
{
"family_name": "Hall",
"given_name": "Jeffrey",
"clpid": "Hall-J"
}
],
"abstract": "Computational models are developed to predict the natural convection heat transfer and buoyancy for a Montgolfiere under conditions relevant to the Titan atmosphere. Idealized single and double-walled balloon geometries are simulated using algorithms suitable for both laminar and (averaged) turbulent convection. Steady-state performance results are compared to existing heat transfer coefficient correlations. The laminar results, in particular, are used to test the validity of the correlations in the absence of uncertainties associated with turbulence modeling. Some discrepancies are observed, especially for convection in the gap, and appear to be primarily associated with temperature nonuniformity on the balloon surface. The predicted buoyancy for the single-walled balloon in the turbulent convection regime, predicted with a standard k \u2212 \u03b5 turbulence model, was within 10% of predictions based on the empirical correlations. There was also good agreement with recently conducted experiments in a cryogenic facility designed to simulate the Titan atmosphere.",
"doi": "10.2514/6.2009-2806",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2009-05"
},
{
"id": "authors:vpng6-8s224",
"collection": "authors",
"collection_id": "vpng6-8s224",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320667",
"type": "conference_item",
"title": "Supersonic Jet Noise from Round and Chevron Nozzles: Experimental Studies",
"author": [
{
"family_name": "Schlinker",
"given_name": "R. H.",
"clpid": "Schlinker-R-H"
},
{
"family_name": "Simonich",
"given_name": "J. C.",
"clpid": "Simonich-J-C"
},
{
"family_name": "Shannon",
"given_name": "D. W.",
"clpid": "Shannon-D-W"
},
{
"family_name": "Reba",
"given_name": "R. A.",
"clpid": "Reba-R-A"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Gudmundsson",
"given_name": "K.",
"clpid": "Gudmundsson-K"
},
{
"family_name": "Ladeinde",
"given_name": "F.",
"clpid": "Ladeinde-F"
}
],
"abstract": "High speed exhaust noise reduction continues to be a research challenge for supersonic cruise business jets as well as for current and future tactical military aircraft. Significant noise reduction may be possible from advanced concepts for controlling instability generated large-scale turbulence structures in the jet shear layer, generally accepted to be the source of aft-angle noise. In response to this opportunity, our team is focused on experimental diagnostic studies and unique instability modeling suited for identifying control strategies to reduce large scale structure noise. The current paper benchmarks the jet noise from supersonic nozzles designed to provide the supporting experimental data and validation of the modeling. Laboratory scale jet noise experiments are presented for a Mach number of Mj = 1.5 with stagnation temperature ratios ranging from Tr = 0.75 to 2. The baseline configuration is represented by a round converging-diverging (CD) ideal expansion nozzle. A round CD nozzle with chevrons is included as the first of several planned non-circular geometries directed at demonstrating the impact on large scale structure noise and validating noise prediction methods for geometries of future technological interest. Overexpanded and underexpanded conditions were tested on both nozzle configurations. The resulting data base provides an opportunity to benchmark the statistical characteristics of round and chevron nozzle data. The current paper examines far field spectra, directivity patterns, and overall sound pressure level dependence comparing observed characteristics with the fine scale turbulence noise and large-scale turbulence structure noise characteristics identified by Tam. In addition, the paper probes the effect of chevrons on the developing flow field and suppression of screech tones. Measurements are also reported from a far-field narrow aperture phased array system used to map the acoustic source distribution on the jet axis. The dominant source region, situated between the end of the potential core and the sonic point, was found to agree with the peak amplitude location of the jet near field wavepackets measured using a unique near field array. This observation supports the cause-effect link between large-scale turbulence structures in the shear layer and their dominant contribution to aft radiated far field noise.",
"doi": "10.2514/6.2009-3257",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2009-05"
},
{
"id": "authors:524xd-fsr23",
"collection": "authors",
"collection_id": "524xd-fsr23",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102318035",
"type": "conference_item",
"title": "In vivo simulation of shock wave lithotripsy: Wave focusing in inhomogeneous materials",
"author": [
{
"family_name": "Krimmel",
"given_name": "Jeffrey",
"clpid": "Krimmel-J"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Shock wave generation and focusing in electrohydraulic, electromagnetic, and piezoelectric lithotripters are simulated numerically. Inhomogeneities associated with wave propagation in vivo are modeled using data from The Visible Human Project. The approximate time\u2010domain relaxation model of Yang and Cleveland (2005) was used to simulate attenuation and dispersion in the tissuelike media. The simulations utilize a MUSCL\u2010type shock capturing scheme with adaptive mesh refinement (AMR). In vitro focal region pressure measurements compare favorably with available experimental data for each lithotripter type. Preliminary in vivo simulation results show significant dispersion associated with the nonuniform sound speed, including increases of up to 50% in focal pressure amplitudes and the presence of multiple pressure minima/maxima in the focal waveform. We will also discuss the extension of the AMR framework to account for cavitation via a previously developed ensemble\u2010averaged continuous two\u2010phase flow model.",
"doi": "10.1121/1.4783996",
"publication_date": "2009-04-09"
},
{
"id": "authors:frnmk-28536",
"collection": "authors",
"collection_id": "frnmk-28536",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20090629-092825317",
"type": "article",
"title": "Three-dimensional flows around low-aspect-ratio flat-plate wings at low Reynolds numbers",
"author": [
{
"family_name": "Kunihiko",
"given_name": "Taira",
"clpid": "Kunihiko-Taira"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Three-dimensional flows over impulsively translated low-aspect-ratio flat plates are investigated for Reynolds numbers of 300 and 500, with a focus on the unsteady vortex dynamics at post-stall angles of attack. Numerical simulations, validated by an oil tow-tank experiment, are performed to study the influence of aspect ratio, angle of attack and planform geometry on the wake vortices and the resulting forces on the plate. Immediately following the impulsive start, the separated flows create wake vortices that share the same topology for all aspect ratios. At large time, the tip vortices significantly influence the vortex dynamics and the corresponding forces on the wings. Depending on the aspect ratio, angle of attack and Reynolds number, the flow at large time reaches a stable steady state, a periodic cycle or aperiodic shedding. For cases of high angles of attack, an asymmetric wake develops in the spanwise direction at large time. The present results are compared to higher Reynolds number flows. Some non-rectangular planforms are also considered to examine the difference in the wakes and forces. After the impulsive start, the time at which maximum lift occurs is fairly constant for a wide range of flow conditions during the initial transient. Due to the influence of the tip vortices, the three-dimensional dynamics of the wake vortices are found to be quite different from the two-dimensional von K\u00e1rm\u00e1n vortex street in terms of stability and shedding frequency.",
"doi": "10.1017/S0022112008005314",
"issn": "0022-1120",
"publisher": "Cambridge",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2009-03-25",
"volume": "623",
"pages": "187-207"
},
{
"id": "authors:nx7jr-csp53",
"collection": "authors",
"collection_id": "nx7jr-csp53",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091009-082632397",
"type": "article",
"title": "Effect of Tip Vortices in Low-Reynolds-Number Poststall Flow Control",
"author": [
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We numerically investigate the application of steady blowing to three-dimensional stalled flows around low-aspect-ratio rectangular flat-plate wings at a Reynolds number of 300. The objective of this study is to explore\ntechniques to enhance lift by directly modifying the dynamics of the wake vortices. Out of various combinations of\nforcing location and direction considered, we identify two configurations that provide significant lift enhancement. In\nthese cases, actuation appears to strengthen the tip vortices for increased downward induced velocity upon the\nleading-edge vortices. This in turn moves the low-pressure core directly above the top surface of the wing to greatly\nenhance lift.",
"doi": "10.2514/1.40615",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2009-03",
"series_number": "3",
"volume": "47",
"issue": "3",
"pages": "749-756"
},
{
"id": "authors:nw5da-r9t24",
"collection": "authors",
"collection_id": "nw5da-r9t24",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320309",
"type": "conference_item",
"title": "On the Effect of Tip Vortices in Low-Reynolds-Number Post-Stall Flow Control",
"author": [
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We numerically investigate the application of steady blowing to three-dimensional stalled flows around low-aspect-ratio rectangular flat-plate wings at a Reynolds number of 300. The objective of this study is to explore techniques to enhance lift by directly modifying the dynamics of the wake vortices. Out of various combinations of forcing location and direction considered, we identify two configurations that provide significant lift enhancement. In these cases, actuation appears to strengthen the tip vortices for increased downward induced velocity upon the leading-edge vortices. This in turn moves the low-pressure core directly above the top surface of the wing to greatly enhance lift.",
"doi": "10.2514/6.2009-376",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2009-01"
},
{
"id": "authors:pxaz0-anz31",
"collection": "authors",
"collection_id": "pxaz0-anz31",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102319638",
"type": "conference_item",
"title": "Low Reynolds Number Wing Response to an Oscillating Freestream With and Without Feed Forward Control",
"author": [
{
"family_name": "Williams",
"given_name": "David",
"clpid": "Williams-D"
},
{
"family_name": "Quach",
"given_name": "Vien",
"clpid": "Quach-V"
},
{
"family_name": "Kerstens",
"given_name": "Wesley",
"clpid": "Kerstens-W"
},
{
"family_name": "Buntain",
"given_name": "Seth",
"clpid": "Buntain-S"
},
{
"family_name": "Tadmor",
"given_name": "Gilead",
"clpid": "Tadmor-G"
},
{
"family_name": "Rowley",
"given_name": "Clarence",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The unsteady lift of a low Reynolds number wing in an oscillating freestream is documented in terms of its amplitude and phase. The phase variation of the lift relative to the freestream velocity shows a larger phase difference than predicted by classical unsteady flow theory. A constant time delay between the lift and the actuator was observed to be \u03c4^+ = t_(delay)U/c = 5.3 when normalized by the freestream speed and chord. Feed forward control of pulsed-jet actuators is used to modulate the lift coefficient of the wing, in an attempt to suppress the lift oscillations. Suppression of the fluctuating lift at the fundamental frequency was partially successful, but additional \"noise\" was added to harmonics of the lift signal by the controller.",
"doi": "10.2514/6.2009-143",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2009-01"
},
{
"id": "authors:ckqq1-wqs11",
"collection": "authors",
"collection_id": "ckqq1-wqs11",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:JOHjasa08",
"type": "article",
"title": "Shock-induced collapse of a gas bubble in shockwave lithotripsy",
"author": [
{
"family_name": "Johnsen",
"given_name": "Eric",
"clpid": "Johnsen-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The shock-induced collapse of a pre-existing nucleus near a solid surface in the focal region of a lithotripter is investigated. The entire flow field of the collapse of a single gas bubble subjected to a lithotripter pulse is simulated using a high-order accurate shock- and interface-capturing scheme, and the wall pressure is considered as an indication of potential damage. Results from the computations show the same qualitative behavior as that observed in experiments: a re-entrant jet forms in the direction of propagation of the pulse and penetrates the bubble during collapse, ultimately hitting the distal side and generating a water-hammer shock. As a result of the propagation of this wave, wall pressures on the order of 1 GPa may be achieved for bubbles collapsing close to the wall. The wall pressure decreases with initial stand-off distance and pulse width and increases with pulse amplitude. For the stand-off distances considered in the present work, the wall pressure due to bubble collapse is larger than that due to the incoming shockwave; the region over which this holds may extend to ten initial radii. The present results indicate that shock-induced collapse is a mechanism with high potential for damage in shockwave lithotripsy.",
"doi": "10.1121/1.2973229",
"issn": "0001-4966",
"publisher": "Acoustical Society of America",
"publication": "Journal of the Acoustical Society of America",
"publication_date": "2008-10",
"series_number": "4",
"volume": "124",
"issue": "4",
"pages": "2011-2020"
},
{
"id": "authors:ay8fn-69b90",
"collection": "authors",
"collection_id": "ay8fn-69b90",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126161",
"type": "conference_item",
"title": "Interaction of Acoustic Disturbances with Micro-Cavities for Ultrasonic Absorptive Coatings",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Fedorov",
"given_name": "Alexander V.",
"clpid": "Fedorov-A-V"
}
],
"abstract": "Numerical simulations are performed to investigate the interaction of acoustic waves with an array of equally-spaced two-dimensional micro-cavities on an otherwise flat plate without external boundary-layer flow. This acoustic scattering problem is important in the design of ultrasonic absorptive coatings (UAC) for hypersonic laminar flow control. The reflection coefficient, characterizing the ratio of the reflected wave amplitude to the incident wave amplitude, is computed as a function of the acoustic wave frequency and angle of incidence, for coatings of different porosity, at various acoustic Reynolds numbers relevant to hypersonic flight. Overall, the numerical results validate predictions from existing theoretical modeling. In general, the amplitude of the reflection coefficient has local minima at some specific frequencies. A simple model to predict these frequencies is presented. The simulations also highlight the presence of resonant acoustic modes caused by coupling of small-scale scattered waves near the UAC surface. Finally, the cavity depth and the porosity are identified as the most important parameters for UAC design. Guidelines for the choice of these parameters are suggested.",
"doi": "10.2514/6.2008-3903",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-06"
},
{
"id": "authors:6h8ep-hra38",
"collection": "authors",
"collection_id": "6h8ep-hra38",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320405",
"type": "conference_item",
"title": "Control of a Semi-Circular Planform Wing in a \"Gusting\" Unsteady Free Stream Flow II: Modeling and Feedback Design",
"author": [
{
"family_name": "Tadmor",
"given_name": "Gilead",
"clpid": "Tadmor-G"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
},
{
"family_name": "Collins",
"given_name": "Jesse",
"clpid": "Collins-Jesse"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
}
],
"abstract": "Active flow control has been demonstrated in Part I of this article to modify the lift, drag and pitching moments on a semi-circular wing during \"gusting\" flow conditions. The low aspect ratio wing, AR = 2.54, is mounted on a captive trajectory system that responds to the instantaneous lift force and pitching moment and the \"gusting\" flow is simulated by a 0.2 Hz oscillation of the free stream speed of the wind tunnel. The mean chord Reynolds number of the wing is 70,600. Active flow control occurs along the leading edge of the airfoil, which contains 16 spatially localized micro-valve actuators. Details of the experimental setup, a quasi steady state lift model and results involving open-loop proof of concept validation are provided in Part I of this paper. Here we outline principles and considerations associated with close loop design that will be discussed in our talk.",
"doi": "10.2514/6.2008-3977",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-06"
},
{
"id": "authors:qw3ea-1hn26",
"collection": "authors",
"collection_id": "qw3ea-1hn26",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102319947",
"type": "conference_item",
"title": "Control of a Semi-Circular Planform Wing in a \"Gusting\" Unsteady Freestream Flow: I - Experimental Issues",
"author": [
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
},
{
"family_name": "Collins",
"given_name": "Jesse",
"clpid": "Collins-Jesse"
},
{
"family_name": "Tadmor",
"given_name": "Gilead",
"clpid": "Tadmor-G"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Active flow control is used to modify the lift, drag and pitching moments on a semicircular wing during \"gusting\" flow conditions. A longitudinal oscillating flow component has an amplitude of 10 percent of the freestream speed and a frequency giving k = 0.048 (f = 0.2 Hz). The aspect ratio of the wing is AR = 2.54, and the chord Reynolds number of the wing is 70,600. Pulsed-blowing flow control actuation occurs along the leading edge of the airfoil via 16 spatially localized micro-valve actuators. Feed-forward control based on a quasi-steady lift model is used to stabilize lift fluctuations generated by an oscillating free stream, which simulates the longitudinal component of a gusting flow. The quasi-steady system model reduces the amplitude of the fundamental and first harmonics of lift oscillations, but does not account for time delays. The time delay between the lift and the freestream oscillation was measured to be \u03c4_(u)^(+) = 4.8. The time delay between the lift and the actuator input signal was found to be \u03c4_(a)^(+) = 11.3.",
"doi": "10.2514/6.2008-3976",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-06"
},
{
"id": "authors:gzafe-1pf52",
"collection": "authors",
"collection_id": "gzafe-1pf52",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320576",
"type": "conference_item",
"title": "Fast Approximated POD for a Flat Plate Benchmark with a Time Varying Angle of Attack",
"author": [
{
"family_name": "Tadmor",
"given_name": "Gilead",
"clpid": "Tadmor-G"
},
{
"family_name": "Bissex",
"given_name": "Daniel",
"clpid": "Bissex-Daniel"
},
{
"family_name": "Noack",
"given_name": "Bernd R.",
"clpid": "Noack-Bernd-R"
},
{
"family_name": "Morzy\u0144ski",
"given_name": "Marek",
"clpid": "Morzy\u0144ski-Marek"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
}
],
"abstract": "An approximate POD algorithm provides an empirical Galerkin approximation with guaranteed a priori lower bound on the required resolution. The snapshot ensemble is partitioned into several sub-ensembles. Cross correlations between these sub-ensembles are approximated in terms of a far smaller correlation matrix. Computational speedup is nearly linear in the number of partitions, up to a saturation that can be estimated a priori. The algorithm is particularly suitable for analyzing long transient trajectories of high dimensional simulations, but can be applied also for spatial partitioning and parallel processing of very high spatial dimension data. The algorithm is demonstrated using transient data from two simulations. First, a two dimensional simulation of the flow over a flat plate, as it transitions from AOA = 30\u00b0 to a horizontal position and back. Second, a three dimensional simulation of a flat plate with aspect ratio two as it transitions from a horizontal position to AOA = 30\u00b0.",
"doi": "10.2514/6.2008-4191",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-06"
},
{
"id": "authors:x6sqk-8vq79",
"collection": "authors",
"collection_id": "x6sqk-8vq79",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320488",
"type": "conference_item",
"title": "Temporal-Harmonic Specific POD Mode Extraction",
"author": [
{
"family_name": "Tadmor",
"given_name": "Gilead",
"clpid": "Tadmor-G"
},
{
"family_name": "Bissex",
"given_name": "Daniel",
"clpid": "Bissex-Daniel"
},
{
"family_name": "Noack",
"given_name": "Bernd R.",
"clpid": "Noack-Bernd-R"
},
{
"family_name": "Morzy\u0144ski",
"given_name": "Marek",
"clpid": "Morzy\u0144ski-Marek"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
}
],
"abstract": "While POD / PCA / KL approximations are statistically energetically optimal, statistical optimality is indeed the sole consideration these (equivalent) methods invoke. This type of approximation is neither geared for, nor is it optimized to extract modes based on their significance to an underlying system dynamics. Furthermore, as computational considerations limit the size of empirical ensembles used for mode extraction, the resulting mode set is significantly effected by the arbitrariness of the ensemble selection. System theoretic model reductions methods aim to home on dynamically significant modes by direct interrogation of the underlying equation, such as the linearized Navier-Stokes equations. An alternative / complimentary approach is to impose a priori knowledge of structural properties, such as symmetry and periodicity, on the mode-extraction procedure. The idea is that these conditions will force the selection of physically meaningful modes, and thus enables an effective appeal to first principles. Here we focus on systems known to be periodically dominant, and describe a simple method to extract modes associated with temporal harmonics. The method accommodates time variations in the dominant frequency(ies) and exploits a preliminary data compression, such as by the standard POD procedure.",
"doi": "10.2514/6.2008-4190",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-06"
},
{
"id": "authors:v3r9s-ztr60",
"collection": "authors",
"collection_id": "v3r9s-ztr60",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320932",
"type": "conference_item",
"title": "Closed-Loop Control of Leading Edge Vorticity on a 3D Wing: Simulations and Low-Dimensional Models",
"author": [
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Ahuja",
"given_name": "Sunil",
"clpid": "Ahuja-Sunil"
},
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We study model-based feedback control of the low-Reynolds-number flow over a flat plate at large angles of attack, in both two and three dimensions. Our long-term goal is to be able to manipulate the leading-edge vortices that form on low-aspect-ratio wings at high angles of attack, and that often contribute to exceptionally large lift coefficients. Intwo-dimensional simulations, we present a model-based feedback controller that uses an observer to reconstruct the entire flow field from velocity measurements at three locations, and stabilizes the flow at an angle of attack for which the natural flow state is periodic shedding. In three-dimensional simulations, we use open-loop forcing to study actuator placement, and conclude that trailing-edge actuation is more effective than leading-edge actuation in influencing the forces on the plate, as well as the wake structures. Finally, we present initial results towards extending our model-based control design to the 3D setting, and apply a selective frequency damping method to find unstable equilibrium flow fields in 3D simulations.",
"doi": "10.2514/6.2008-3981",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-06"
},
{
"id": "authors:fpvvg-zzx85",
"collection": "authors",
"collection_id": "fpvvg-zzx85",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126067",
"type": "conference_item",
"title": "Stability of Temporally Evolving Supersonic Boundary Layers over Micro-Cavities for Ultrasonic Absorptive Coatings",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Fedorov",
"given_name": "Alexander V.",
"clpid": "Fedorov-A-V"
}
],
"abstract": "Ultrasonic absorptive coatings, consisting of regularly-spaced arrays of micro-cavities, have previously been shown to effectively damp second-mode instability for the purpose of delaying transition in hypersonic boundary layers. However, previous simulations and stability analysis have used approximate porous-wall boundary conditions. Here we investigate the feasibility of using direct numerical simulation to directly compute the hypersonic boundary layer including the micro-cavities. In order to keep the problem computationally tractable, we restrict our attention to the two-dimensional case (which is relevant since the second-mode is initially two dimensional), and we show that temporally evolving layers display qualitatively similar behavior to spatially developing boundary layer and instabilities. We validate the numerical method by comparing the simulation results to temporal linear stability analysis of the (frozen) velocity and temperature profiles from the direct numerical simulation. Two-dimensional linear simulations of the boundary layer on a flat plate and over a porous coating are performed, and it is shown that the presence of the cavities attenuates the instability waves, as expected from theory.",
"doi": "10.2514/6.2008-4337",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-06"
},
{
"id": "authors:v9x61-yz433",
"collection": "authors",
"collection_id": "v9x61-yz433",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102318220",
"type": "conference_item",
"title": "Damage potential of single\u2010bubble collapse in shockwave lithotripsy",
"author": [
{
"family_name": "Johnsen",
"given_name": "Eric",
"clpid": "Johnsen-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "In shockwave lithotripsy, the combined effect of focused shockwaves and cavitation pulverizes kidney stones. Although cavitation is known to play an important role in stone comminution, the underlying mechanism is not fully understood. The goal of the present study is to quantify the potential damage caused by Rayleigh collapse (RC) and shock\u2010induced collapse (SIC) of a single bubble near a stone. A high\u2010order accurate, quasi\u2010conservative, shock\u2010 and interface\u2010capturing scheme [E. Johnsen and T. Colonius, J. Comput. Phys. 2006] is employed to simulate both phenomena. A high\u2010speed re\u2010entrant jet forms during the collapse and hits the distal side of the bubble, thereby generating a water\u2010hammer pressure wave. A high pressure is measured along the stone surface upon the impact of this wave, thus providing potential for erosion. In SIC, this pressure may reach 1 GPa and bubbles within approximately 15 initial radii generate a pressure higher than the incoming pulse. In addition, by using the present results as time\u2010dependent boundary conditions for an elastic wave propagation code, it is shown that a tension large enough to lead to failure may be achieved within small stones or fragments.",
"doi": "10.1121/1.2933980",
"publication_date": "2008-05-09"
},
{
"id": "authors:adbbn-2va10",
"collection": "authors",
"collection_id": "adbbn-2va10",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102317947",
"type": "conference_item",
"title": "Numerical simulation of shock wave generation and focusing in shock wave lithotripsy",
"author": [
{
"family_name": "Krimmel",
"given_name": "Jeffrey",
"clpid": "Krimmel-J"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Shock wave lithotripsy is a procedure where focused shock waves are fired at kidney stones in order to pulverize them. Lithotripters with different source mechanisms and reflector shapes (or lenses) are in clinical use, but prediction of focal region pressure is made difficult by nonlinearity and cavitation. We report on development of a numerical simulation framework aimed at accurate prediction of focal region pressures and bubble dynamics. Shock wave generation and beam focusing are simulated via the Euler equations with MUSCL\u2010type shock\u2010capturing scheme and adaptive mesh refinement (AMR). Electrohydraulic, electromagnetic, and piezoelectric\u2010array lithotripters are modeled with axisymmetric geometries. In the electrohydraulic case, an expanding bubble model simulates spark firing. In the piezoelectric case, a boundary condition prescribing the motion of individual elements is used. Calculated peak pressures and pulse widths agree well with experimental data for the electrohydraulic and electromagnetic lithotripters. For the piezoelectric case, peak pressures are increasingly over\u2010predicted by the model when more elements are fired, and reasons for this discrepancy will be discussed. Finally, we compare the spatial and temporal characteristics of the focal pressure fields for several clinical lithotripters in the context of observed stone comminution efficacy and tissue damage.",
"doi": "10.1121/1.2933977",
"publication_date": "2008-05-09"
},
{
"id": "authors:7anqp-90624",
"collection": "authors",
"collection_id": "7anqp-90624",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320761",
"type": "conference_item",
"title": "Decomposition of High Speed Jet Noise: Source Characteristics and Propagation Effects",
"author": [
{
"family_name": "Schlinker",
"given_name": "R. H.",
"clpid": "Schlinker-R-H"
},
{
"family_name": "Simonich",
"given_name": "J. C.",
"clpid": "Simonich-J-C"
},
{
"family_name": "Reba",
"given_name": "R. A.",
"clpid": "Reba-R-A"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Ladeinde",
"given_name": "F.",
"clpid": "Ladeinde-F"
}
],
"abstract": "Current research programs directed at supersonic engine exhaust noise reduction are demonstrating benefits of 3-4 dBA using passive methods to increase jet mixing and break up shock cells in over-expanded flows. While progress is being made, high speed jet noise continues to be a research challenge for small business jets and tactical military aircraft. The current work benchmarks high speed jet noise using laboratory scale jets for the purpose of a) identifying source and propagation mechanisms, and b) providing validation data for simulation/modeling methods. Laboratory scale experiments are presented over a Mach number range of M = 0.68 to 1.5 with static temperature ratio ranging from Tr = 0.68 to 2. A unique near field rotating phased microphone array technique was used to identify the large-scale turbulence structure noise source and Mach waves in supersonic shock-free jets. A companion paper documents the near field pressure statistics and projection of the convected wave packet to the far field. Validation against the directly measured far field levels quantitatively establishes the large scale structure noise contributions. The combined studies underpin a long term effort to develop modeling methods and new concepts for jet noise suppression based on controlling the evolution of the large-scale turbulence structures.",
"doi": "10.2514/6.2008-2890",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-05"
},
{
"id": "authors:knvkc-frk46",
"collection": "authors",
"collection_id": "knvkc-frk46",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100505-140942697",
"type": "article",
"title": "A fast immersed boundary method using a nullspace approach and multi-domain far-field boundary conditions",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
}
],
"abstract": "We report on the continued development of a projection approach for implementing the immersed boundary method for incompressible flows in two and three dimensions. Boundary forces and pressure are regarded as Lagrange multipliers that enable the no-slip and divergence-free constraints to be implicitly determined to arbitrary precision with no associated time-step restrictions. In order to accelerate the method, we further implement a nullspace (discrete streamfunction) method that allows the divergence-free constraint to be automatically satisfied to machine roundoff. By employing a fast sine transform technique, the linear system to determine the forces can be solved efficiently with direct or iterative techniques. A multi-domain technique is developed in order to improve far-field boundary conditions that are compatible with the fast sine transform and account for the extensive potential flow induced by the body as well as vorticity that advects/diffuses to large distance from the body. The multi-domain and fast techniques are validated by comparing to the exact solutions for the potential flow induced by stationary and propagating Oseen vortices and by an impulsively-started circular cylinder. Speed-ups of more than an order-of-magnitude are achieved with the new method.",
"doi": "10.1016/j.cma.2007.08.014",
"issn": "0045-7825",
"publisher": "Elsevier",
"publication": "Computer Methods in Applied Mechanics and Engineering",
"publication_date": "2008-04-15",
"series_number": "25-28",
"volume": "197",
"issue": "25-28",
"pages": "2131-2146"
},
{
"id": "authors:rj4h4-z6k80",
"collection": "authors",
"collection_id": "rj4h4-z6k80",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:COLpof08",
"type": "article",
"title": "Statistical equilibrium of bubble oscillations in dilute bubbly flows",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Hagmeijer",
"given_name": "Rob",
"clpid": "Hagmeijer-R"
},
{
"family_name": "Ando",
"given_name": "Keita",
"clpid": "Ando-Keita"
},
{
"family_name": "Brennen",
"given_name": "Christopher E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "The problem of predicting the moments of the distribution of bubble radius in bubbly flows is considered. The particular case where bubble oscillations occur due to a rapid (impulsive or step change) change in pressure is analyzed, and it is mathematically shown that in this case, inviscid bubble oscillations reach a stationary statistical equilibrium, whereby phase cancellations among bubbles with different sizes lead to time-invariant values of the statistics. It is also shown that at statistical equilibrium, moments of the bubble radius may be computed using the period-averaged bubble radius in place of the instantaneous one. For sufficiently broad distributions of bubble equilibrium (or initial) radius, it is demonstrated that bubble statistics reach equilibrium on a time scale that is fast compared to physical damping of bubble oscillations due to viscosity, heat transfer, and liquid compressibility. The period-averaged bubble radius may then be used to predict the slow changes in the moments caused by the damping. A benefit is that period averaging gives a much smoother integrand, and accurate statistics can be obtained by tracking as few as five bubbles from the broad distribution. The period-averaged formula may therefore prove useful in reducing computational effort in models of dilute bubbly flow wherein bubbles are forced by shock waves or other rapid pressure changes, for which, at present, the strong effects caused by a distribution in bubble size can only be accurately predicted by tracking thousands of bubbles. Some challenges associated with extending the results to more general (nonimpulsive) forcing and strong two-way coupled bubbly flows are briefly discussed.",
"doi": "10.1063/1.2912517",
"issn": "1070-6631",
"publisher": "American Institute of Physics",
"publication": "Physics of Fluids",
"publication_date": "2008-04",
"series_number": "4",
"volume": "20",
"issue": "4",
"pages": "Art. No. 040902"
},
{
"id": "authors:tzsbh-1f356",
"collection": "authors",
"collection_id": "tzsbh-1f356",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:BREjfm08",
"type": "article",
"title": "Three-dimensional instabilities in compressible flow over open cavities",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Direct numerical simulations are performed to investigate the three-dimensional stability of compressible flow over open cavities. A linear stability analysis is conducted to search for three-dimensional global instabilities of the two-dimensional mean flow for cavities that are homogeneous in the spanwise direction. The presence of such instabilities is reported for a range of flow conditions and cavity aspect ratios. For cavities of aspect ratio (length to depth) of 2 and 4, the three-dimensional mode has a spanwise wavelength of approximately one cavity depth and oscillates with a frequency about one order of magnitude lower than two-dimensional Rossiter (flow/acoustics) instabilities. A steady mode of smaller spanwise wavelength is also identified for square cavities. The linear results indicate that the instability is hydrodynamic (rather than acoustic) in nature and arises from a generic centrifugal instability mechanism associated with the mean recirculating vortical flow in the downstream part of the cavity. These three-dimensional instabilities are related to centrifugal instabilities previously reported in flows over backward-facing steps, lid-driven cavity flows and Couette flows. Results from three-dimensional simulations of the nonlinear compressible Navier\u2013Stokes equations are also reported. The formation of oscillating (and, in some cases, steady) spanwise structures is observed inside the cavity. The spanwise wavelength and oscillation frequency of these structures agree with the linear analysis predictions. When present, the shear-layer (Rossiter) oscillations experience a low-frequency modulation that arises from nonlinear interactions with the three-dimensional mode. The results are consistent with observations of low-frequency modulations and spanwise structures in previous experimental and numerical studies on open cavity flows.",
"doi": "10.1017/S0022112007009925",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2008-03-25",
"volume": "599",
"pages": "309-339"
},
{
"id": "authors:xqb9x-tw623",
"collection": "authors",
"collection_id": "xqb9x-tw623",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102318299",
"type": "conference_item",
"title": "Closed-Loop Control of Vortex Shedding on a Two-Dimensional Flat-Plate Airfoil at a Low Reynolds Number",
"author": [
{
"family_name": "Joe",
"given_name": "Won Tae",
"clpid": "Joe-Won-Tae"
},
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "MacMynowski",
"given_name": "Douglas G.",
"orcid": "0000-0003-1987-9417",
"clpid": "MacMartin-D-G"
},
{
"family_name": "Tadmor",
"given_name": "Gilead",
"clpid": "Tadmor-G"
}
],
"abstract": "Open- and closed-loop control of vortex shedding in two-dimensional flow over a flat plate at high angles of attack is numerically investigated at a Reynolds number of 300. Unsteady actuation is modeled as a body force near the leading or trailing edge, and is directed either upstream or downstream. For moderate angles of attack, sinusoidal forcing at the natural shedding frequency results in phase locking, with a periodic variation of lift at the same frequency. However, at sufficiently high angles of attack, subharmonics of the forcing frequency are also excited and the average lift over the forcing period varies from cycle to cycle in a complex manner. It is observed that the periods with the highest averaged lift are associated with particular phase difference between the forcing and the lift. We design a feedback algorithm to lock the forcing with the phase shift associated with the highest period-averaged lift. It is shown that the compensator results in a stable phaselocked limit cycle for a larger range of forcing frequencies than the open-loop control, and that it is able to stabilize otherwise unstable high-lift limit cycles that cannot be obtained with open-loop control. For example at an angle of attack of 40\u00b0, the feedback controller can increase the averaged lift coefficient from 1.35 to 2.43, an increase of 80%.",
"doi": "10.2514/6.2008-634",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-01"
},
{
"id": "authors:gbm0n-6cf77",
"collection": "authors",
"collection_id": "gbm0n-6cf77",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102321018",
"type": "conference_item",
"title": "A New Low Reynolds Number Facility for Active Flow Control Applications",
"author": [
{
"family_name": "Munson",
"given_name": "Matthew J.",
"clpid": "Munson-M-J"
},
{
"family_name": "Dickson",
"given_name": "William B.",
"clpid": "Dickson-W-B"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Gharib",
"given_name": "Morteza",
"orcid": "0000-0003-0754-4193",
"clpid": "Gharib-M"
}
],
"abstract": "Recent interest in gaining understanding of the dynamics and behavior of the leading-edge vortex structure observed in biological flight systems has prompted the construction of a new low Reynolds number facility. This facility, a recirculating oil tunnel, gives several distinct advantages over similar facilities, utilizing water or air as the working fluid, for this kind of study. Additionally, as understanding is gained, active flow control strategies leading to the stabilization of the leading-edge vortex structure will be investigated, and this facility is specially equipped to enable this study. The tunnel has been designed and installed at the California Institute of Technology Graduate Aeronautical Laboratories. Design features of the facility will be discussed, along with some preliminary measurements conducted on a NACA 0012 wing.",
"doi": "10.2514/6.2008-694",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-01"
},
{
"id": "authors:d2d1q-h1w55",
"collection": "authors",
"collection_id": "d2d1q-h1w55",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125978",
"type": "conference_item",
"title": "Unsteady Aerodynamic Forces on Small-Scale Wings: Experiments, Simulations, and Models",
"author": [
{
"family_name": "Brunton",
"given_name": "Steven L.",
"clpid": "Brunton-S-L"
},
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Collins",
"given_name": "Jesse",
"clpid": "Collins-Jesse"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
}
],
"abstract": "The goal of this work is to develop low order dynamical systems models for the unsteady lift and drag forces on small wings in various modes of flight, and to better understand the physical characteristics of unsteady laminar separation. Velocity field and body force data for a flat plate at static angle of attack and in sinusoidal pitch and plunge maneuvers are generated by 2D direct numerical simulations using an immersed boundary method at Re = 100. The lift of a sinusoidally plunging plate is found to deviate from the quasi-steady approximation at a reduced frequency of k = 0.5 over a range of Strouhal numbers. Lagrangian coherent structures illustrate formation and convection of a leading-edge vortex in sinusoidal pitch and plunge. A phenomenological ODE model with three states is shown to reproduce the lift on a flat plate at a static angle of attack above the stall angle. DNS for a 3D pitch-up maneuver of a rectangular plate at Re = 300 shows the effect of aspect ratio on vortical wake structure and lift. Wind tunnel experiments of a wing in single pitch-up and sinusoidal pitch maneuvers are compared with a dynamic model incorporating time delays and relaxation times to produce hysteresis.",
"doi": "10.2514/6.2008-520",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-01"
},
{
"id": "authors:4c369-hcr19",
"collection": "authors",
"collection_id": "4c369-hcr19",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320045",
"type": "conference_item",
"title": "Control of Flow Structure on a Semi-Circular Planform Wing",
"author": [
{
"family_name": "Williams",
"given_name": "D.",
"clpid": "Williams-D"
},
{
"family_name": "Collins",
"given_name": "J.",
"clpid": "Collins-J"
},
{
"family_name": "Jankhot",
"given_name": "C.",
"clpid": "Jankhot-C"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Tadmor",
"given_name": "Gilead",
"clpid": "Tadmor-G"
}
],
"abstract": "Active flow control is used to modify the lift, drag and pitching moments on a semicircular wing with aspect ratio, AR = 2, and chord Reynolds number is 68,000. The wing is mounted on a pitch/plunge sting mechanism that responds to the instantaneous loads and moments acting on the wing. The leading edge of the airfoil contains 16 spatially localized actuators that can be independently controlled. Smoke wire visualization, surface pressure and six-component force balance measurements are used to characterize the effects of openloop forcing. The lift coefficients on the steady wing are enhanced with the actuation, similar to the effect of dynamic stall vortex lift enhancement that occurs during a pitch up maneuver. Surface pressure measurements are being used to construct a flow model for use in feedback control. Progress toward the goal of designing a feedback controller to stabilize the flight of the model in an oscillatory freestream is discussed.",
"doi": "10.2514/6.2008-597",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-01"
},
{
"id": "authors:gp7xp-5dt27",
"collection": "authors",
"collection_id": "gp7xp-5dt27",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125724",
"type": "conference_item",
"title": "Large-Eddy Simulation of Separation Control for Compressible Flow Over a Wall-Mounted Hump",
"author": [
{
"family_name": "Franck",
"given_name": "Jennifer A.",
"clpid": "Franck-J-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Compressible large-eddy simulations of turbulent flow over a wall-mounted hump with active flow control are performed and compared to previous experiments. We consider a range of Mach numbers from 0.1 to 0.6. Control is applied just before the natural separation point via steady suction and zero-net mass flux oscillatory forcing. Compared with the baseline flow, control shortens the separation bubble length, but is generally found to be less effective at compressible Mach numbers. The LES matches well to the available experimental data for the baseline and steady suction cases. With oscillatory forcing, the LES captures the major flow physics of the large scale shedding of vortical structures, but over-predicts the separation bubble length at low Mach numbers.",
"doi": "10.2514/6.2008-555",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2008-01"
},
{
"id": "authors:thjxd-ev812",
"collection": "authors",
"collection_id": "thjxd-ev812",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100810-092143228",
"type": "book_section",
"title": "Non-spherical collapse of an air bubble subjected to a lithotripter pulse",
"book_title": "Biomedical and biotechnology engineering",
"author": [
{
"family_name": "Johnsen",
"given_name": "Eric",
"clpid": "Johnsen-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Kreider",
"given_name": "Wayne",
"clpid": "Kreider-W"
},
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-M-R"
}
],
"abstract": "In order to better understand the contribution of bubble collapse\nto stone comminution in shockwave lithotripsy, the shockinduced\nand Rayleigh collapse of a spherical air bubble is investigated\nusing numerical simulations, and the free-field collapse of\na cavitation bubble is studied experimentally. In shock-induced\ncollapse near a wall, it is found that the presence of the bubble\ngreatly amplifies the pressure recorded at the stone surface; the\nfunctional dependence of the wall pressure on the initial standoff\ndistance and the amplitude are presented. In Rayleigh collapse\nnear a solid surface, the proximity of the wall retards the\nflow and leads to a more prominent jet. Experiments show that\nre-entrant jets form in the collapse of cavitation bubbles excited\nby lithotripter shockwaves in a fashion comparable to previous\nstudies of collapse near a solid surface.",
"doi": "10.1115/IMECE2007-43156",
"isbn": "978-0-7918-4296-6",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "2008",
"pages": "285-294"
},
{
"id": "authors:g69gt-k6264",
"collection": "authors",
"collection_id": "g69gt-k6264",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:PREpof07",
"type": "article",
"title": "A reduced-order model of diffusive effects on the dynamics of bubbles",
"author": [
{
"family_name": "Preston",
"given_name": "A. T.",
"clpid": "Preston-A-T"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "C. E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "We propose a new reduced-order model for spherical bubble dynamics that accurately captures the effects of heat and mass diffusion. The objective is to reduce the full system of partial differential equations to a set of coupled ordinary differential equations that are efficient enough to implement into complex bubbly flow computations. Comparisons to computations of the full partial differential equations and of other reduced-order models are used to validate the model and establish its range of validity.",
"doi": "10.1063/1.2825018",
"issn": "1070-6631",
"publisher": "American Institute of Physics",
"publication": "Physics of Fluids",
"publication_date": "2007-12",
"series_number": "12",
"volume": "19",
"issue": "12",
"pages": "Art. No. 123302"
},
{
"id": "authors:qtb98-cpe50",
"collection": "authors",
"collection_id": "qtb98-cpe50",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125075",
"type": "article",
"title": "A Cumulative Shear Mechanism for Tissue Damage Initiation in Shock-Wave Lithotripsy",
"author": [
{
"family_name": "Freund",
"given_name": "Jonathan B.",
"clpid": "Freund-J-B"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Evan",
"given_name": "Andrew P.",
"clpid": "Evan-A-P"
}
],
"abstract": "Evidence suggests that inertial cavitation plays an important role in the renal injury incurred during shock-wave lithotripsy. However, it is unclear how tissue damage is initiated, and significant injury typically occurs only after a sufficient dose of shock waves. Although it has been suggested that shock-induced shearing might initiate injury, estimates indicate that individual shocks do not produce sufficient shear to do so. In this paper, we hypothesize that the cumulative shear of the many shocks is damaging. This mechanism depends on whether there is sufficient time between shocks for tissue to relax to its unstrained state. We investigate the mechanism with a physics-based simulation model, wherein the basement membranes that define the tubules and vessels in the inner medulla are represented as elastic shells surrounded by viscous fluid. Material properties are estimated from in-vitro tests of renal basement membranes and documented mechanical properties of cells and extracellular gels. Estimates for the net shear deformation from a typical lithotripter shock (similar to 0.1 %) are found from a separate dynamic shock simulation. The results suggest that the larger interstitial volume (similar to 40%) near the papilla tip gives the tissue there a relaxation time comparable to clinical shock delivery rates (similar to 1 Hz), thus allowing shear to accumulate. Away from the papilla tip, where the interstitial volume is smaller (similar to 20%), the model tissue relaxes completely before the next shock would be delivered. Implications of the model are that slower delivery rates and broader focal zones should both decrease injury, consistent with some recent observations.",
"doi": "10.1016/j.ultrasmedbio.2007.03.001",
"issn": "0301-5629",
"publisher": "Elsevier",
"publication": "Ultrasound in Medicine and Biology",
"publication_date": "2007-09",
"series_number": "9",
"volume": "33",
"issue": "9",
"pages": "1495-1503"
},
{
"id": "authors:5cggc-2dg45",
"collection": "authors",
"collection_id": "5cggc-2dg45",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165128384",
"type": "article",
"title": "The Immersed Boundary Method: A Projection Approach",
"author": [
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "A new formulation of the immersed boundary method with a structure algebraically identical to the traditional fractional step method is presented for incompressible flow over bodies with prescribed surface motion. Like previous methods, a boundary force is applied at the immersed surface to satisfy the no-slip constraint. This extra constraint can be added to the incompressible Navier\u2013Stokes equations by introducing regularization and interpolation operators. The current method gives prominence to the role of the boundary force acting as a Lagrange multiplier to satisfy the no-slip condition. This role is analogous to the effect of pressure on the momentum equation to satisfy the divergence-free constraint. The current immersed boundary method removes slip and non-divergence-free components of the velocity field through a projection. The boundary force is determined implicitly without any constitutive relations allowing the present formulation to use larger CFL numbers compared to some past methods. Symmetry and positive-definiteness of the system are preserved such that the conjugate gradient method can be used to solve for the flow field. Examples show that the current formulation achieves second-order temporal accuracy and better than first-order spatial accuracy in L2-norms for one- and two-dimensional test problems. Results from two-dimensional simulations of flows over stationary and moving cylinders are in good agreement with those from previous experimental and numerical studies.",
"doi": "10.1016/j.jcp.2007.03.005",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2007-08-10",
"series_number": "2",
"volume": "225",
"issue": "2",
"pages": "2118-2137"
},
{
"id": "authors:pne1h-27m31",
"collection": "authors",
"collection_id": "pne1h-27m31",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-081956579",
"type": "book_section",
"title": "Spatial Stability Analysis of Chevron Jet Profiles",
"book_title": "13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)",
"author": [
{
"family_name": "Gudmundsson",
"given_name": "Kristjan",
"clpid": "Gudmundsson-K"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We investigate the linear stability characteristics of mean flows produced by round, and chevron nozzles. We derive a Rayleigh equation for the chevron profile, which allows the\nfast solution of the chevron stability problem. Using PIV and RANS data, we compute the stability characteristics of various chevron/round nozzles. We find there are two main\ndifferences between the chevron and round jet: chevron jet growth rates are highly suppressed and peak growth rates shifted to lower frequencies, and phase speeds are somewhat\nincreased. Some preliminary implications on sound generation are discussed. We compare our instability wave results to microphone measurements taken with a phased hydrodynamic array. Our results indicate that the hydrodynamic pressure field of both round, and\nchevron jets is consistent with that of the instability modes of the turbulent, spreading mean flow.",
"doi": "10.2514/6.2007-3599",
"isbn": "978-1-62410-003-1",
"publisher": "American Institute of Aeronautics and Astronautics",
"place_of_publication": "Reston, VA",
"publication_date": "2007-05",
"pages": "1-14"
},
{
"id": "authors:rd6j7-tdz57",
"collection": "authors",
"collection_id": "rd6j7-tdz57",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126239",
"type": "conference_item",
"title": "Direct Numerical Simulations of Three-Dimensional Cavity Flows",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Three-dimensional direct numerical simulations of the full compressible Navier\u2013Stokes equations are performed for cavities that are homogeneous in the spanwise direction. The formation of oscillating spanwise structures is observed inside the cavity. We show that this 3D instability arises from a generic centrifugal instability mechanism associated with the mean recirculating vortical flow in the downstream part of the cavity. In general, the three-dimensional mode has a spanwise wavelength of approximately 1 cavity depth and oscillates with a frequency about an order-of-magnitude lower than 2D Rossiter (flow/acoustics) instabilities. The 3D mode properties are in excellent agreement with predictions from our previous linear stability analysis. When present, the shear-layer (Rossiter) oscillations experience a low-frequency modulation that arises from nonlinear interactions with the three-dimensional mode. We connect these results with the observation of low-frequency modulations and spanwise structures in previous experimental and numerical studies on open cavity flows. Preliminary results on the connections between the 3D centrifugal instabilities and the presence/suppression of the wake mode are also presented.",
"doi": "10.2514/6.2007-3405",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2007-05"
},
{
"id": "authors:zsnjw-pqj51",
"collection": "authors",
"collection_id": "zsnjw-pqj51",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20100923-144204048",
"type": "book_section",
"title": "Numerical study of the collapse of a bubble subjected to a lithotripter pulse",
"book_title": "Renal stone disease",
"author": [
{
"family_name": "Johnsen",
"given_name": "Eric",
"clpid": "Johnsen-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"contributor": [
{
"family_name": "Evan",
"given_name": "Andrew P.",
"clpid": "Evan-A-P"
},
{
"family_name": "Lingemen",
"given_name": "James E.",
"clpid": "Lingemen-J-E"
},
{
"family_name": "Williams",
"given_name": "James C., Jr.",
"clpid": "Williams-J-C-Jr"
}
],
"abstract": "The collapse of a bubble subjected to a lithotripter pulse is studied numerically. The goal is to record the pressure exerted along the stone, as a measure of potential stone damage. It is found that the pressure due to buble collapse is much larger than that of the lithotripter pulse. Furthermore, the pressure greatly depends on the geometry of the problem (initial stand-off distance and bubble size) and on the properties of the pulse (amplitude and width).",
"doi": "10.1063/1.2723596",
"isbn": "978-0-7354-0406-9",
"publisher": "American Institute of Physics",
"place_of_publication": "Melville, NY",
"publication_date": "2007-04-05",
"pages": "360-363"
},
{
"id": "authors:q6gyy-kp129",
"collection": "authors",
"collection_id": "q6gyy-kp129",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126320",
"type": "conference_item",
"title": "Three-Dimensional Linear Stability Analysis of Cavity Flows",
"author": [
{
"family_name": "Br\u00e8s",
"given_name": "Guillaume A.",
"orcid": "0000-0003-2507-8659",
"clpid": "Br\u00e8s-G-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Numerical Simulations of the two- and three-dimensional linearized Navier\u2013Stokes equations are performed to investigate instabilities of open cavity flows that are homogeneous in the spanwise direction. First, the onset of two-dimensional cavity instability is characterized over a range of Mach numbers, Reynolds numbers and cavity aspect ratios. The resulting oscillations are consistent with the typical Rossiter flow/acoustic resonant modes. We then identify the presence of three-dimensional instabilities of the two-dimensional basic flow and study their dependence on the parameter space. In general, the most amplified three-dimensional mode has a spanwise wavelength scaling with the cavity depth, and a frequency typically an order-of-magnitude smaller than two-dimensional Rossiter modes. The instability appears to arise from a generic centrifugal instability mechanism associated with a large vortex in the two-dimensional basic flow that occupies the downstream portion within the cavity.",
"doi": "10.2514/6.2007-1126",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2007-01"
},
{
"id": "authors:g50jc-hpg03",
"collection": "authors",
"collection_id": "g50jc-hpg03",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125547",
"type": "conference_item",
"title": "Low-Dimensional Models for Control of Leading-Edge Vortices: Equilibria and Linearized Models",
"author": [
{
"family_name": "Ahuja",
"given_name": "Sunil",
"clpid": "Ahuja-Sunil"
},
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Kevrekidis",
"given_name": "Ioannis G.",
"clpid": "Kevrekidis-I-G"
},
{
"family_name": "Wei",
"given_name": "Mingjun",
"clpid": "Wei-Mingjun"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Tadmor",
"given_name": "Gilead",
"clpid": "Tadmor-G"
}
],
"abstract": "When an airfoil is pitched up rapidly, a dynamic stall vortex forms at the leading edge and produces high transient lift before shedding and stall occur. The aim of this work is to develop low-dimensional models of the dynamics of these leading-edge vortices, which may be used to develop feedback laws to stabilize these vortices using closed-loop control, and maintain high lift. We first perform a numerical study of the two-dimensional incompressible flow past an airfoil at varying angles of attack, finding steady states using a timestepper-based Newton/GMRES scheme, and dominant eigenvectors using ARPACK. These steady states may be either stable or unstable; we develop models linearized about the stable steady states using a method called Balanced Proper Orthogonal Decomposition, an approximation of balanced truncation that is tractable for large systems. The balanced POD models dramatically outperform models using the standard POD/Galerkin procedure, and are used to develop observers that reconstruct the flow state from a single surface pressure measurement.",
"doi": "10.2514/6.2007-709",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2007-01"
},
{
"id": "authors:e5m7e-s3b33",
"collection": "authors",
"collection_id": "e5m7e-s3b33",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165127033",
"type": "conference_item",
"title": "Unsteadiness in Flow over a Flat Plate at Angle-of-Attack at Low Reynolds Numbers",
"author": [
{
"family_name": "Taira",
"given_name": "Kunihiko",
"orcid": "0000-0002-3762-8075",
"clpid": "Taira-Kunihiko"
},
{
"family_name": "Dickson",
"given_name": "William B.",
"clpid": "Dickson-W-B"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Dickinson",
"given_name": "Michael H.",
"orcid": "0000-0002-8587-9936",
"clpid": "Dickinson-M-H"
},
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
}
],
"abstract": "Flow over an impulsively started low-aspect-ratio flat plate at angle-of-attack is investigated for a Reynolds number of 300. Numerical simulations, validated by a companion experiment, are performed to study the influence of aspect ratio, angle of attack, and planform geometry on the interaction of the leading-edge and tip vortices and resulting lift and drag coefficients. Aspect ratio is found to significantly influence the wake pattern and the force experienced by the plate. For large aspect ratio plates, leading-edge vortices evolved into hairpin vortices that eventually detached from the plate, interacting with the tip vortices in a complex manner. Separation of the leading-edge vortex is delayed to some extent by having convective transport of the spanwise vorticity as observed in flow over elliptic, semicircular, and delta-shaped planforms. The time at which lift achieves its maximum is observed to be fairly constant over different aspect ratios, angles of attack, and planform geometries during the initial transient. Preliminary results are also presented for flow over plates with steady actuation near the leading edge.",
"doi": "10.2514/6.2007-710",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2007-01"
},
{
"id": "authors:zg6ay-f1h85",
"collection": "authors",
"collection_id": "zg6ay-f1h85",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126500",
"type": "conference_item",
"title": "Control of the Spanwise Distribution of Circulation on NACA 0012 and Flat Plate Wings",
"author": [
{
"family_name": "Williams",
"given_name": "D.",
"clpid": "Williams-D"
},
{
"family_name": "Doshi",
"given_name": "S.",
"clpid": "Doshi-S"
},
{
"family_name": "Collins",
"given_name": "J.",
"clpid": "Collins-J"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Open-loop active flow control is used to modify the spanwise distribution of circulation around an NACA 0012 and flat plate wing. The leading edge on both airfoils and tip regions of the NACA airfoil contain spatially localized actuators that can be independently controlled in terms of amplitude and frequency, allowing the spanwise distribution of circulation to be modified. Different orientations of the pulsed-blowing actuators were used to provide upstream, downstream, in-line with the flow, and outward span components of actuation. The actuation effectiveness was documented using force balance measurements of the lift and drag, smoke-wire visualization, surface pressure measurements and PIV velocity field measurements. Actuation with an upstream component is shown to be far more effective in reducing the separated region than actuation in the streamwise direction. Initial measurements of the change in circulation on the suction surface of the airfoil indicate that spatially localized forcing produces global changes over the wing, primarily associated with the reduction in size of the separated flow region.",
"doi": "10.2514/6.2007-1121",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2007-01"
},
{
"id": "authors:smjdh-yhx43",
"collection": "authors",
"collection_id": "smjdh-yhx43",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165128280",
"type": "article",
"title": "Implementation of WENO Schemes in Compressible Multicomponent Flow Problems",
"author": [
{
"family_name": "Johnsen",
"given_name": "Eric",
"clpid": "Johnsen-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "High-order accurate shock-capturing schemes are capable of properly resolving discontinuities with correct wave speeds in single-fluid Riemann problems. However, when different fluids are present, oscillations develop at interfaces. A class of existing interface-capturing methods that suppress these oscillations is based on first- and second-order accurate reconstructions with Roe solvers. In this paper, we extend these methods to high-order accurate WENO schemes and the HLLC approximate Riemann solver. In particular, we show that a finite volume formulation where the appropriately averaged primitive variables are reconstructed leads to the oscillation-free advection of an isolated interface. Furthermore, numerical experiments show no spurious oscillations for problems where shockwaves and interfaces interact. We solve the Euler equations supplemented by a stiffened equation of state to model flows of gas and liquid components. Our method is high-order accurate, quasi-conservative, shock-capturing and interface-capturing; these properties are additionally verified by considering one-dimensional multicomponent Riemann problems and a two-dimensional shock\u2013bubble interaction.",
"doi": "10.1016/j.jcp.2006.04.018",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2006-12-10",
"series_number": "2",
"volume": "219",
"issue": "2",
"pages": "715-732"
},
{
"id": "authors:3h917-p4w37",
"collection": "authors",
"collection_id": "3h917-p4w37",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165128473",
"type": "conference_item",
"title": "Numerical Study of the Collapse of a Bubble Subjected to a Lithotripter Pulse",
"author": [
{
"family_name": "Johnsen",
"given_name": "Eric",
"clpid": "Johnsen-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "In shock wave lithotripsy, the combined effect of focused shock waves and cavitation pulverizes kidney stones. Although cavitation has been shown to play an important role in the stone comminution process, the underlying mechanism has yet to be fully understood. The goal of the present study is to quantify the potential damage caused by the collapse of a single bubble near a solid surface. Using a high\u2010order accurate quasiconservative, shock\u2010 and interface\u2010capturing scheme [E. Johnsen and T. Colonius, J. Comput. Phys., in press (2006)], the response of an air bubble subjected to a lithotripter pulse is considered. In particular, quantities important in cavitation erosion, such as wall stresses and reentrant jet velocity, are measured as functions of the properties of the pulse (amplitude, wavelength) and the geometry of the problem (stand\u2010off distance from the wall, presence of neighboring bubbles). Preliminary two\u2010dimensional results for a ''cylindrical bubble'' show that a large water\u2010hammer pressure is measured along the wall. This pressure increases for smaller stand\u2010off distances and longer wavelengths. Further results for spherical bubbles will be presented at the meeting.",
"doi": "10.1121/1.4787344",
"publisher": "The Journal of the Acoustical Society of America",
"publication_date": "2006-11"
},
{
"id": "authors:z459a-4n506",
"collection": "authors",
"collection_id": "z459a-4n506",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:SUZjfm06b",
"type": "article",
"title": "Instability waves in a subsonic round jet detected using a near-field phased microphone array",
"author": [
{
"family_name": "Suzuki",
"given_name": "Takao",
"clpid": "Suzuki-Takao"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We propose a diagnostic technique to detect instability waves in a subsonic round jet using a phased microphone array. The detection algorithm is analogous to the beam-forming technique, which is typically used with a far-field microphone array to localize noise sources. By replacing the reference solutions used in the conventional beam-forming with eigenfunctions from linear stability analysis, the amplitudes of instability waves in the axisymmetric and first two azimuthal modes are inferred. Experimental measurements with particle image velocimetry and a database from direct numerical simulation are incorporated to design a conical array that is placed just outside the mixing layer near the nozzle exit. The proposed diagnostic technique is tested in experiments by checking for consistency of the radial decay, streamwise evolution and phase correlation of hydrodynamic pressure. The results demonstrate that in a statistical sense, the pressure field is consistent with instability waves evolving in the turbulent mean flow from the nozzle exit to the end of the potential core, particularly near the most amplified frequency of each azimuthal mode. We apply this technique to study the effects of jet Mach number and temperature ratio on the azimuthal mode balance and evolution of instability waves. We also compare the results from the beam-forming algorithm with the proper orthogonal decomposition and discuss some implications for jet noise.",
"doi": "10.1017/S0022112006001613",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2006-10",
"volume": "565",
"pages": "197-226"
},
{
"id": "authors:ghkwc-yh566",
"collection": "authors",
"collection_id": "ghkwc-yh566",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125634",
"type": "book_section",
"title": "Compressible Multicomponent Flow Calculations and Shock-Bubble Interaction",
"author": [
{
"family_name": "Johnsen",
"given_name": "Eric",
"clpid": "Johnsen-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We report on the development of a numerical method to simulate two-dimensional compressible multicomponent flows. Our scheme is shock- and interface-capturing, quasi-conservative and high-order accurate. We validate it for two-dimensional problems including shock-bubble interactions and examine the shockinduced asymetric collapse of a cylindrical gas bubble in water, where wave strengths and pulse durations are chosen to model conditions relevant to shockwave lithotripsy. In particular, we determine how the pressure at the surface of a nearby wall depends on the various properties of the pulse and on the geometry. We also describe the extension of the method to axisymmetric geometry and show preliminary results.",
"publisher": "Maritime Research Institute Netherlands",
"publication_date": "2006-09"
},
{
"id": "authors:t39zw-5gz04",
"collection": "authors",
"collection_id": "t39zw-5gz04",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-074713989",
"type": "book_section",
"title": "Linear Stability Analysis of Chevron Jet Profiles",
"book_title": "ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering",
"author": [
{
"family_name": "Gudmundsson",
"given_name": "Kristjan",
"clpid": "Gudmundsson-K"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We investigate the linear stability characteristics of the mean velocity profiles produced by chevron nozzles. We show that chevron instability waves can be decomposed into azimuthal modes analogously to those of round jets. This facilitates a direct comparison of growth rates and mode structure between different nozzles. We find that the three nozzles used in this study share a set of modes, referred to as primary modes. In addition, we find that there exist modes unique to the chevrons nozzles, termed secondary modes. While chevron jets possess a much larger number of unstable modes, the modes with lowest azimuthal structure show strong suppression of growth rates in two different chevron jets. Some preliminary implications on sound generation are discussed.",
"doi": "10.1115/FEDSM2006-98485",
"isbn": "0-7918-4751-9",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "2006-07",
"pages": "497-504"
},
{
"id": "authors:kq0p5-yz865",
"collection": "authors",
"collection_id": "kq0p5-yz865",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125363",
"type": "article",
"title": "Progress in Lithotripsy Research",
"author": [
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-M-R"
},
{
"family_name": "McAteer",
"given_name": "James A.",
"clpid": "McAteer-J-A"
},
{
"family_name": "Pishchalnikov",
"given_name": "Yuri A.",
"clpid": "Pishchalnikov-Y-A"
},
{
"family_name": "Hamilton",
"given_name": "Mark F.",
"clpid": "Hamilton-Mark-F"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Shock wave lithotripsy (SWL) for the non-invasive treatment of kidney stones was introduced in the United States in 1984. SWL virtually eliminated the need for open surgery to remove kidney stones, and it did not take long for physicians and patients to endorse this revolutionary technology. Early reports told of the efficient removal of even the most troublesome stones without apparent complications, and SWL quickly became the \"treatment modality of choice.\" It was not long, however, before concerned physicians began to report the occurrence of adverse effects in SWL, particularly involving vascular trauma and including cases of severe hemorrhage in the kidney and acute renal failure \u2014 significant side effects of serious consequence. Researchers quickly recognized the challenge and opportunity to determine the mechanisms of shock wave action in lithotripsy, and in 1988, the Acoustical Society of America held the first in a series of popular sessions devoted to the topic of shock waves in medicine. The goal of the inaugural session was to improve the fundamental understanding of lithotripsy \u2014 to bring better devices and treatments to patients. The goal of this paper is to report on progress in this effort.",
"issn": "1557-0215",
"publisher": "Acoustical Society of America",
"publication": "Acoustics Today",
"publication_date": "2006-04",
"series_number": "2",
"volume": "2",
"issue": "2",
"pages": "18-29"
},
{
"id": "authors:cs1cy-78146",
"collection": "authors",
"collection_id": "cs1cy-78146",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:ROWjfm06",
"type": "article",
"title": "Linear models for control of cavity flow oscillations",
"author": [
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Murray",
"given_name": "Richard M.",
"orcid": "0000-0002-5785-7481",
"clpid": "Murray-R-M"
},
{
"family_name": "MacMynowski",
"given_name": "Douglas G.",
"orcid": "0000-0003-1987-9417",
"clpid": "MacMartin-D-G"
}
],
"abstract": "Models for understanding and controlling oscillations in the flow past a rectangular cavity are developed. These models may be used to guide control designs, to understand performance limits of feedback, and to interpret experimental results. Traditionally, cavity oscillations are assumed to be self-sustained: no external disturbances are necessary to maintain the oscillations, and amplitudes are limited by nonlinearities. We present experimental data which suggests that in some regimes, the oscillations may not be self-sustained, but lightly damped: oscillations are sustained by external forcing, such as boundary-layer turbulence. In these regimes, linear models suffice to describe the behaviour, and the final amplitude of oscillations depends on the characteristics of the external disturbances. These linear models are particularly appropriate for describing cavities in which feedback has been used for noise suppression, as the oscillations are small and nonlinearities are less likely to be important. It is shown that increasing the gain too much in such feedback control experiments can lead to a peak-splitting phenomenon, which is explained by the linear models. Fundamental performance limits indicate that peak splitting is likely to occur for narrow-bandwidth actuators and controllers.",
"doi": "10.1017/S0022112005007299",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2006-01-25",
"volume": "547",
"pages": "317-330"
},
{
"id": "authors:8tye4-y3v75",
"collection": "authors",
"collection_id": "8tye4-y3v75",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165127273",
"type": "conference_item",
"title": "Relation Between Instability Waves and Low-Frequency Jet Noise Investigated with Phased-Microphone Arrays",
"author": [
{
"family_name": "Suzuki",
"given_name": "Takao",
"clpid": "Suzuki-Takao"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We study the relation between sound radiation patterns and the azimuthal-mode balance of instability-wave amplitude in a subsonic jet using mid-field and near-field phased- microphone arrays. To identify instability waves, we apply a least square optimization method, i.e. a beam-forming algorithm, to pressure signals obtained from a conical microphone array surrounding the jet from the nozzle exit to the end of the potential core. For the reference solutions, we use eigenfunctions based on linear stability analysis using the turbulent mean-velocity profiles and infer the amplitude of the axisymmetric and first two azimuthal modes associated with the Kelvin\u2014Helmholtz instabilities. Likewise, pressure signals obtained from the mid-field array are decomposed into the azimuthal modes, and the directivity of low-frequency noise, particularly that of coherent sound, is analyzed. The azimuthal mode balances of the instability waves and acoustic waves are then compared, and the effects of compressibility, jet temperature and nozzle type (i.e. straight and chevron nozzles) are investigated. The results show that the directivity of low-frequency jet noise changes from the quadrupole radiation patterns to highly directive ones as increasing Mach number, while all instability modes are suppressed owing to compressibility without substantially varying the azimuthal-mode balance. The correlation of the azimuthal-mode balance between instability waves and coherent sound is stronger at higher Mach numbers. We also find that the radiation patterns of low-frequency noise change from quadrupoles to dipoles as the temperature increases at a low Mach number.",
"doi": "10.2514/6.2006-622",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2006-01"
},
{
"id": "authors:0s615-kqj40",
"collection": "authors",
"collection_id": "0s615-kqj40",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165127504",
"type": "conference_item",
"title": "Modeling Jet Noise from Organized Structures Using Near-Field Hydrodynamic Pressure",
"author": [
{
"family_name": "Reba",
"given_name": "R.",
"clpid": "Reba-R-A"
},
{
"family_name": "Narayanan",
"given_name": "S.",
"clpid": "Narayanan-S"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Suzuki",
"given_name": "T.",
"clpid": "Suzuki-Takao"
}
],
"abstract": "A wave-packet ansatz is used to model noise generation by organized, large-scale structures. The spectrum of the acoustic field is expressed in terms of two-point space-time correlations of hydrodynamic pressure on a conical surface surrounding the jet plume. The surface is sufficiently near the turbulent flow region to be dominated by hydrodynamic disturbances, yet sufficiently far that the wave equation can be used to project the nearfield pressure to the acoustic field. In the present study, a 78-microphone array was used to measure hydrodynamic pressure on the conical surface at a variety of acoustic Mach numbers and temperature ratios. At each jet cross section, 6 microphones are staggered in the azimuthal direction allowing resolution of pressure up to azimuthal mode number m = 2. We compare recent jet noise measurements using an 80-microphone conical mid-field array with those derived from the near-field hydrodynamic array data, showing reasonably good predictions. Source model parameters are identified for various jet temperature ratios. Results show that changes in jet noise directivity with heating can be attributed to contraction of the wave-packet scale.",
"doi": "10.2514/6.2005-3093",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2005-05"
},
{
"id": "authors:yfga7-6tv34",
"collection": "authors",
"collection_id": "yfga7-6tv34",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:SUZjfm04",
"type": "article",
"title": "Vortex shedding in a two-dimensional diffuser: theory and simulation of separation control by periodic mass injection",
"author": [
{
"family_name": "Suzuki",
"given_name": "Takao",
"clpid": "Suzuki-Takao"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Pirozzoli",
"given_name": "Sergio",
"clpid": "Pirozzoli-S"
}
],
"abstract": "We develop a reduced-order model for large-scale unsteadiness (vortex shedding) in a two-dimensional diffuser and use the model to show how periodic mass injection near the separation point reduces stagnation pressure loss. The model estimates the characteristic frequency of vortex shedding and stagnation pressure loss by accounting for the accumulated circulation due to the vorticity flux into the separated region. The stagnation pressure loss consists of two parts: a steady part associated with the time-averaged static pressure distribution on the wall, and an unsteady part caused by vortex shedding. To validate the model, we perform numerical simulations of compressible unsteady laminar diffuser flows in two dimensions. The model and simulation show good agreement as we vary the Mach number and the area ratio of the diffuser. To investigate the effects of periodic mass injection near the separation point, we also perform simulations over a range of the injection frequencies. Periodic mass injection causes vortices to be pinched off with a smaller size as observed in experiments. Consequently, their convective velocity is increased, absorption of circulation from the wall is enhanced, and the reattached point is shifted upstream. Thus, in accordance with the model, the stagnation pressure loss, particularly the unsteady part, is substantially reduced even though the separation point is nearly unchanged. This study helps explain experimental results of separation control using unsteady mass injection in diffusers and on airfoils.",
"doi": "10.1017/S0022112004001405",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2004-12-10",
"volume": "520",
"pages": "187-213"
},
{
"id": "authors:fbxcw-3en51",
"collection": "authors",
"collection_id": "fbxcw-3en51",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126641",
"type": "article",
"title": "A Model for Kidney Tissue Damage under High Speed Loading",
"author": [
{
"family_name": "Weinberg",
"given_name": "Kerstin",
"clpid": "Weinberg-K"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Ortiz",
"given_name": "Michael",
"orcid": "0000-0001-5877-4824",
"clpid": "Ortiz-M"
}
],
"abstract": "In a medical procedure to comminute kidney stones the patient is subjected to hypersonic waves focused at the stone. Unfortunately such shock waves also damage the surrounding kidney tissue. We present here a model for the mechanical response of the soft tissue to such a high speed loading regime. \n\nThe material model combines shear induced plasticity with irreversible volumetric expansion as induced, e.g., by cavitating bubbles. The theory is based on a multiplicative decomposition of the deformation gradient and on an internal variable formulation of continuum thermodynamics. By the use of logarithmic and exponential mappings the stress update algorithms are extended from small\u2010strain to the finite deformation range. In that way the time\u2010discretized version of the porous\u2010viscoplastic constitutive updates is described in a fully variational manner. \n\nBy numerical experiments we study the shock\u2010wave propagation into the tissue and analyze the resulting stress states. A first finite element simulation shows localized damage in the human kidney.",
"doi": "10.1002/pamm.200410098",
"issn": "1617-7061",
"publisher": "Wiley",
"publication": "Proceedings in Applied Mathematics and Mechanics",
"publication_date": "2004-12",
"series_number": "1",
"volume": "4",
"issue": "1",
"pages": "234-235"
},
{
"id": "authors:twjng-6yq95",
"collection": "authors",
"collection_id": "twjng-6yq95",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-075725469",
"type": "article",
"title": "Computational aeroacoustics: progress on nonlinear problems of sound generation",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
}
],
"abstract": "Computational approaches are being developed to study a range of problems in aeroacoustics. These aeroacoustic problems may be classified based on the physical processes responsible for the sound radiation, and range from linear problems of radiation, refraction, and scattering in known base flows or by solid bodies, to sound generation by turbulence. In this article, we focus mainly on the challenges and successes associated with numerically simulating sound generation by turbulent flows. \n\nWe discuss a hierarchy of computational approaches that range from semi-empirical schemes that estimate the noise sources using mean-flow and turbulence statistics, to high-fidelity unsteady flow simulations that resolve the sound generation process by direct application of the fundamental conservation principles. We stress that high-fidelity methods such as Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) have their merits in helping to unravel the flow physics and the mechanisms of sound generation. They also provide rich databases for modeling activities that will ultimately be needed to improve existing predictive capabilities. \n\nSpatial and temporal discretization schemes that are well-suited for aeroacoustic calculations are analyzed, including the effects of artificial dispersion and dissipation on uniform and nonuniform grids. We stress the importance of the resolving power of the discretization as well as computational efficiency of the overall scheme. Boundary conditions to treat the flow of disturbances in and out of the computational domain, as well as methods to mimic anechoic domain extension are discussed. Test cases on some benchmark problems are included to provide a realistic assessment of several boundary condition treatments.\n\nFinally, highlights of recent progress are given using selected model problems. These include subsonic cavity noise and jet noise. In the end, the current challenges in aeroacoustic modeling and in simulation algorithms are revisited with a look toward the future developments.",
"doi": "10.1016/j.paerosci.2004.09.001",
"issn": "0376-0421",
"publisher": "Elsevier",
"publication": "Progress in Aerospace Sciences",
"publication_date": "2004-08",
"series_number": "6",
"volume": "40",
"issue": "6",
"pages": "345-416"
},
{
"id": "authors:4ex9f-gvt30",
"collection": "authors",
"collection_id": "4ex9f-gvt30",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126795",
"type": "conference_item",
"title": "Three-dimensional instabilities of compressible flow over open cavities: direct solution of the BiGlobal eigenvalue problem",
"author": [
{
"family_name": "Theofilis",
"given_name": "V.",
"clpid": "Theofilis-V"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We report progress in our ongoing effort to compute and understand the instabilities of open cavity flows from incompressible to supersonic speeds. We consider three-dimensional instabilities of nominally two dimensional (spanwise homogeneous) cavity flows (BiGlobal instabilities). Experiments, DNS/LES computations, and preliminary instability computations have shown that the modes of oscillation are influenced by complex interactions between the shear layer and the recirculating flow within the cavity. We present here a framework for computation of the two-dimensional eigenvalue problem for the compressible open cavity. We validate the numerical scheme by computing several canonical flows: square duct flow, boundary layers at speeds from incompressible to supersonic, and two-dimensional parallel shear layers. We present preliminary results for the three-dimensional modes of the compressible open cavity flow with length-to-depth ratio of two at a Mach number of 0.325.",
"doi": "10.2514/6.2004-2544",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2004-06"
},
{
"id": "authors:5g3ht-by565",
"collection": "authors",
"collection_id": "5g3ht-by565",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165127351",
"type": "conference_item",
"title": "Identification of Jet Instability Waves and Design of a Microphone Array",
"author": [
{
"family_name": "Suzuki",
"given_name": "Takao",
"clpid": "Suzuki-Takao"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We propose a diagnostic technique to detect instability waves in a round jet using a conical microphone array. The detection algorithm is analogous to the beam-forming technique, which is used with a far-field microphone array to localize noise sources. By replacing the reference solutions used in the conventional beam-forming with eigenfunctions from a linear stability analysis, the amplitude of the low-frequency azimuthal instability waves can be inferred. We use a DNS database and experimental measurements of the mean flow to design a phased microphone array which is placed just outside the shear layer near the nozzle exit. We validate the technique in experiments by checking for consistency of the radial decay, phase correlation, and streamwise evolution of the hydrodynamic pressure. The comparison between the experiment and linear stability analysis shows good agreement, particularly near the most amplified frequency of each azimuthal mode.",
"doi": "10.2514/6.2004-2960",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2004-05"
},
{
"id": "authors:y1sv4-q3929",
"collection": "authors",
"collection_id": "y1sv4-q3929",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165128101",
"type": "conference_item",
"title": "Numerical Simulation of Sound Radiated from a Turbulent Vortex Ring",
"author": [
{
"family_name": "Ran",
"given_name": "Hongyu",
"clpid": "Ran-Hongyu"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The acoustic field radiated by a turbulent vortex ring is studied. Direct Numerical Simulations (DNS) of the fully compressible, three-dimensional Navier-Stokes equations are used to generate an axisymmetric vortex ring to which 3D stochastic disturbances are added. The disturbances cause instability and turbulent transition of the vortex ring. Detailed information about temporal evolution of sound pressure level, spectrum and directivity associated with each mode is investigated. The peak frequency agrees well with experiments, and the directivity of each azimuthal mode agrees well with predictions of vortex sound theory. Based on the self-similar decay of the turbulent near field, the selfsimilar decay of the sound field is investigated. We also explore the connections with jet noise by modeling the jet as a de-correlated train of vortex rings.",
"doi": "10.2514/6.2004-2918",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2004-05"
},
{
"id": "authors:2fex1-0xr95",
"collection": "authors",
"collection_id": "2fex1-0xr95",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-075224908",
"type": "article",
"title": "Model reduction for compressible flows using POD and Galerkin projection",
"author": [
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Murray",
"given_name": "Richard M.",
"orcid": "0000-0002-5785-7481",
"clpid": "Murray-R-M"
}
],
"abstract": "We present a framework for applying the method of proper orthogonal decomposition (POD) and Galerkin projection to compressible fluids. For incompressible flows, only the kinematic variables are important, and the techniques are well known. In a compressible flow, both the kinematic and thermodynamic variables are dynamically important, and must be included in the configuration space. We introduce an energy-based inner product which may be used to obtain POD modes for this configuration space. We then obtain an approximate version of the Navier\u2013Stokes equations, valid for cold flows at moderate Mach number, and project these equations onto a POD basis. The resulting equations of motion are quadratic, and are much simpler than projections of the full compressible Navier\u2013Stokes equations.",
"doi": "10.1016/j.physd.2003.03.001",
"issn": "0167-2789",
"publisher": "Elsevier",
"publication": "Physica D",
"publication_date": "2004-02-15",
"series_number": "1-2",
"volume": "189",
"issue": "1-2",
"pages": "115-129"
},
{
"id": "authors:6s5ph-btg61",
"collection": "authors",
"collection_id": "6s5ph-btg61",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:COLarfm04",
"type": "article",
"title": "Modeling Artificial Boundary Conditions for Compressible Flow",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We review artificial boundary conditions (BCs) for simulation of inflow, outflow, and far-field (radiation) problems, with an emphasis on techniques suitable for compressible turbulent shear flows. BCs based on linearization near the boundary are usually appropriate for inflow and radiation problems. A variety of accurate techniques have been developed for this case, but some robustness and implementation issues remain. At an outflow boundary, the linearized BCs are usually not accurate enough. Various ad hoc models have been proposed for the nonlinear case, including absorbing layers and fringe methods. We discuss these techniques and suggest directions for future modeling efforts.",
"doi": "10.1146/annurev.fluid.36.050802.121930",
"issn": "0066-4189",
"publisher": "Annual Reviews, Inc.",
"publication": "Annual Review of Fluid Mechanics",
"publication_date": "2004-01",
"volume": "36",
"pages": "315-345"
},
{
"id": "authors:dt21v-dxe02",
"collection": "authors",
"collection_id": "dt21v-dxe02",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165127197",
"type": "conference_item",
"title": "Closed-Loop Control of Vortex Shedding in a Separated Diffuser Using an Inverse Method",
"author": [
{
"family_name": "Suzuki",
"given_name": "Takao",
"clpid": "Suzuki-Takao"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "MacMartin",
"given_name": "Douglas G.",
"orcid": "0000-0003-1987-9417",
"clpid": "MacMartin-D-G"
}
],
"abstract": "We propose a closed-loop control algorithm for vortex shedding in a separated diffuser. We introduce pulses of zero-net-mass injection (consecutive blowing and suction) together with an inverse vortex imaging method. This method estimates the circulation of a vortex in the separated region based on pressure at a limited number of observer points at the wall. The closed-loop algorithm determines when to start the pulse so that the vortex is pinched off with a size which minimizes the stagnation pressure loss. We examine the proposed method in a simplified flow by performing direct numerical simulations of two-dimensional diffusers. In order to investigate the robustness of the closed-loop control algorithm, we impose high frequency acoustic disturbance upstream of the separation point. The disturbances significantly reduce the effectiveness of open-loop control compared to the case where no external disturbances are added. By using closed-loop control, however, performance is once again substantially recovered in the presence of disturbances.",
"doi": "10.2514/6.2004-577",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2004-01"
},
{
"id": "authors:fm63k-rhr43",
"collection": "authors",
"collection_id": "fm63k-rhr43",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126954",
"type": "conference_item",
"title": "Progress in Modeling and Simulation of Shock Wave Lithotripsy (SWL)",
"author": [
{
"family_name": "Tanguay",
"given_name": "Michel",
"clpid": "Tanguay-M"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Past research in shock wave lithotripsy (SWL) has shown that cavitation plays an essential role in the comminution of kidney stones. To provide a better understanding of the role of cloud cavitation dynamics in SWL, the flow in the focal region of a lithotripter was modeled using an ensemble averaged two-phase flow model for the bubbly mixture combined with a high-order accurate shock capturing technique. The domain and initial conditions used in the numerical model reflect the appropriate dimensions and intensity of a Dornier HM3 electrohydraulic lithotripter. The impact of factors such as the size and number of bubble nuclei in the liquid, the intensity of the shock wave and the pulse rate frequency (PRF) on the cavitating flow field is analyzed. Conclusions regarding the impact of these parameters on the potential for stone comminution are also presented.",
"publisher": "Caltech Library",
"publication_date": "2003-11"
},
{
"id": "authors:x7w07-vzt76",
"collection": "authors",
"collection_id": "x7w07-vzt76",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:PREcav03",
"type": "conference_item",
"title": "Reduced-Order Modeling of Diffusive Effects on the Dynamics of Bubbles",
"author": [
{
"family_name": "Preston",
"given_name": "A.",
"clpid": "Preston-A-T"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "C. E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "The Rayleigh-Plesset equation and its extensions have been used extensively to model spherical bubble dynamics, yet radial diffusion equations must be solved to correctly capture damping effects due to mass and thermal diffusion. The latter are too computationally intensive to implement into a continuum model for bubbly cavitating flows, since the diffusion equations must be solved at each position in the flow. The goal of the present research is to derive a reduced-order model that accounts for thermal and mass diffusion. Motivated by results of applying the Proper Orthogonal Decomposition to data from full radial computations, we derive a model based upon estimates of the average heat transfer coefficients. The model captures the damping effects of the diffusion processes in two ordinary differential equations, and gives better results than previous models.",
"publisher": "Caltech Library",
"publication_date": "2003-11"
},
{
"id": "authors:d1bjf-kac10",
"collection": "authors",
"collection_id": "d1bjf-kac10",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-131110058",
"type": "book_section",
"title": "Cavitation in shock wave lithotripsy: the critical role of bubble activity in stone breakage and kidney trauma",
"book_title": "2003 IEEE Symposium on Ultrasonics",
"author": [
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-M-R"
},
{
"family_name": "Cleveland",
"given_name": "Robin O.",
"clpid": "Cleveland-R-O"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Crum",
"given_name": "Lawrence A.",
"clpid": "Crum-L-A"
},
{
"family_name": "Evan",
"given_name": "Andrew P.",
"clpid": "Evan-A-P"
},
{
"family_name": "Lingeman",
"given_name": "James E.",
"clpid": "Lingeman-J-E"
},
{
"family_name": "McAteer",
"given_name": "James A.",
"clpid": "McAteer-J-A"
},
{
"family_name": "Sapozhnikov",
"given_name": "Oleg A.",
"clpid": "Sapozhnikov-O-A"
},
{
"family_name": "Williams",
"given_name": "James C., Jr.",
"clpid": "Williams-J-C-Jr"
}
],
"abstract": "Objective: Shock Wave Lithotripsy (SWL) is the use of shock waves to fragment kidney stones. We have undertaken a study of the physical mechanisms responsible for stone comminution and tissue injury in SWL. SWL was originally developed on the premise that stone fragmentation could be induced by a short duration, high amplitude positive pressure pulse. Even though the SWL waveform carries a prominent tensile component, it has long been thought that SW damage to stones could be explained entirely on the basis of mechanisms such as spallation, pressure gradients, and compressive fracture. We contend that not only is cavitation also involved in SWL, bubble activity plays a critical role in stone breakage and is a key mechanism in tissue damage. Methods: Our evidence is based upon a series of experiments in which we have suppressed or minimized cavitation, and discovered that both stone comminution and tissue injury is similarly suppressed or minimized. Some examples of these experiments are (1) application of overpressure, (2) time reversal of acoustic waveform, (3) acoustically-transparent, cavitation-absorbing films, and (4) dual pulses. In addition, using passive and active ultrasound, we have observed the existence of cavitation, in vivo, and at the site of tissue injury. Results: Numerical and experimental results showed mitigation of bubble collapse intensity by time-reversing the lithotripsy pulse and in vivo treatment showed a corresponding drop from 6.1% \u00b1 1.7% to 0.0% in the hemorrhagic lesion. The time-reversed wave did not break stones. Stone comminution and hemolysis were reduced to levels very near sham levels with the application of hydrostatic pressure greater than the near 10-MPa amplitude of the negative pressure of the lithotripter shock wave. A Mylar sheet 3-mm from the stone surface did not inhibit erosion and internal cracking, but a sheet in contact with the stone did. In water, mass lost from stones in a dual pulse lithotripter is 8 times greater than with a single lithotripter, but in glycerol, which reduces the pressures generated in bubble implosion, the enhancement is lost. Conclusion: This cavitation-inclusive mechanistic understanding of SWL is gaining acceptance and has had clinical impact. Treatment at slower SW rate gives cavitation bubble clusters time to dissolve between pulses and increases comminution. Some SWL centers now treat patients at slower SW rate to take advantage of this effect. An elegant cavitation-aware strategy to reduce renal trauma in SWL is being tested in experimental animals. Starting treatment at low amplitude causes vessels to constrict and this interferes with cavitation-mediated vascular injury. Acceptance of the role of cavitation in SWL is beginning to be embraced by the lithotripter industry, as new dual-pulse lithotripters\u2014based on the concept of cavitation control\u2014 have now been introduced.",
"doi": "10.1109/ultsym.2003.1293503",
"isbn": "0-7803-7922-5",
"publisher": "IEEE",
"place_of_publication": "Piscataway, NJ",
"publication_date": "2003-10",
"pages": "724-727"
},
{
"id": "authors:5hjh7-bg971",
"collection": "authors",
"collection_id": "5hjh7-bg971",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125806",
"type": "conference_item",
"title": "Cloud cavitation effects in shockwave lithotripsy",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Tanguay",
"given_name": "Michel",
"clpid": "Tanguay-M"
}
],
"abstract": "Cavitation has already been identified as an important damage mechanism in the comminution of kidney stones in shockwave lithotripsy (SWL). However, the precise conditions that maximize the damage caused by the collapsing bubbles are still unknown. Numerical simulations are used to investigate shock propagation and the consequent growth and collapse of a bubble cloud in the focal region of a lithotripter. In the simulations, a continuum two\u2010phase flow model for the ensemble\u2010averaged macroscale is coupled to a Gilmore model for individual spherical bubble dynamics at the microscale. The simulations show agreement with experimental pressure measurements and high\u2010speed photography of the bubble cloud. At void fractions commensurate with experiments, it is found that the collective collapse of the bubble cloud provides a significant increase to the energy available for comminution (beyond what a single bubble would produce). Relatively small increases in the pressure at the center of the cloud in advance of collapse (two orders of magnitude smaller than the initial shock) can more than double the energy of the collapsing bubble.",
"doi": "10.1121/1.4779511",
"publication_date": "2003-10"
},
{
"id": "authors:epcjn-2qn64",
"collection": "authors",
"collection_id": "epcjn-2qn64",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165128182",
"type": "conference_item",
"title": "Dynamics of Concerted Bubble Cluster Collapse in Shock Wave Lithotripsy",
"author": [
{
"family_name": "Pishchalnikov",
"given_name": "Yuri A.",
"clpid": "Pishchalnikov-Y-A"
},
{
"family_name": "McAteer",
"given_name": "James A.",
"clpid": "McAteer-J-A"
},
{
"family_name": "Evan",
"given_name": "Andrew P.",
"clpid": "Evan-A-P"
},
{
"family_name": "Sapozhnikov",
"given_name": "Oleg A.",
"clpid": "Sapozhnikov-O-A"
},
{
"family_name": "Cleveland",
"given_name": "Robin O.",
"clpid": "Cleveland-R-O"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-M-R"
},
{
"family_name": "Crum",
"given_name": "Lawrence A.",
"clpid": "Crum-L-A"
}
],
"abstract": "Cavitation bubble cluster collapse at the surface of artificial kidney stones during shock wave lithotripsy was investigated in vitro by means of multiframe high\u2010speed photography, passive cavitation detection (PCD), and pressure waveform measurements using a fiber\u2010optic probe hydrophone (FOPH). It was observed that after the passage of the lithotripter shock pulse the stone was covered by numerous individual bubbles. During their growth phase the bubbles coalesced into bubble clusters, with the biggest cluster at the proximal face of the stone. High\u2010speed camera images suggested that cluster collapse started at the periphery and ended with a violent collapse in a small region in the center of the surface of the stone. Shadowgraphy resolved numerous secondary shock waves emitted during this focused collapse. Shock wave emission during cluster collapse was confirmed by PCD. Measurement with the FOPH showed that these shock waves were typically of short duration (0.2 \u03bcs). The majority of the shock waves emanating from cluster collapse were low amplitude but some shock waves registered amplitudes on the order of the incident shock pulse (tens of MPa).",
"doi": "10.1121/1.4777748",
"publication_date": "2003-10"
},
{
"id": "authors:00sd9-5vh54",
"collection": "authors",
"collection_id": "00sd9-5vh54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125458",
"type": "conference_item",
"title": "Cavitation in shock wave lithotripsy",
"author": [
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-M-R"
},
{
"family_name": "Crum",
"given_name": "Lawrence A.",
"clpid": "Crum-L-A"
},
{
"family_name": "Sapozhnikov",
"given_name": "Oleg A.",
"clpid": "Sapozhnikov-O-A"
},
{
"family_name": "Evan",
"given_name": "Andrew P.",
"clpid": "Evan-A-P"
},
{
"family_name": "McAteer",
"given_name": "James A.",
"clpid": "McAteer-J-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Cleveland",
"given_name": "Robin O.",
"clpid": "Cleveland-R-O"
}
],
"abstract": "A case is presented for the important role of cavitation in stone comminution and tissue injury in shock wave lithotripsy (SWL). Confocal hydrophones and a coincidence algorithm were used to detect cavitation in kidney parenchyma. Elevated hydrostatic pressure dissolved cavitation nuclei and suppressed cell injury and stone comminution in vitro. A low\u2010insertion\u2010loss, thin, mylar film nearly eliminated stone erosion and crack formation only when in direct contact with the stone. This result indicates not only that cavitation is important in both cracking and erosion but also that bubbles act at the surface. Time inversion of the shock wave by use of a pressure\u2010release reflector reduced the calculated pressure at bubble collapse and the measured depth of bubble\u2010induced pits in aluminum. Correspondingly tissue injury in vivo was nearly eliminated. Cavitation was localized and intensified by the use of synchronously triggered, facing lithotripters. This dual pulse lithotripter enhanced comminution at its focus and reduced lysis in surrounding blood samples. The enhancement of comminution was lost when stones were placed in glycerol, which retarded bubble implosion. Thus, cavitation is important in comminution and injury and can be controlled to optimize efficacy and safety.",
"doi": "10.1121/1.4778635",
"publication_date": "2003-10"
},
{
"id": "authors:5y0p5-1gd86",
"collection": "authors",
"collection_id": "5y0p5-1gd86",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125193",
"type": "article",
"title": "Inverse-Imaging Method for Detection of a Vortex in a Channel",
"author": [
{
"family_name": "Suzuki",
"given_name": "Takao",
"clpid": "Suzuki-Takao"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "A simple vortex-imaging algorithm using a least-square method is considered. The position and the circulation of a vortex convected in a channel are identified from the time history of pressure at a limited number of points on the wall. The capabilities of the algorithm are demonstrated using two-dimensional direct numerical simulations. A few observer points on one side of the wall are sufficient to detect the position and the circulation of a compact vortex to a reasonable degree of accuracy. An advanced algorithm can even detect two nearby vortices to the same degree of accuracy. Because the algorithm assumes a point vortex solution, the accuracy of the detection deteriorates as the vorticity distribution spreads.",
"doi": "10.2514/2.7292",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2003-09",
"series_number": "9",
"volume": "41",
"issue": "9",
"pages": "1743-1751"
},
{
"id": "authors:ngawq-0xp65",
"collection": "authors",
"collection_id": "ngawq-0xp65",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170409-075315005",
"type": "article",
"title": "Cavitation Bubble Cluster Activity in the Breakage of Kidney Stones by Lithotripter Shock Waves",
"author": [
{
"family_name": "Pishchalnikov",
"given_name": "Yuriy A.",
"clpid": "Pishchalnikov-Y-A"
},
{
"family_name": "Sapozhnikov",
"given_name": "Oleg A.",
"clpid": "Sapozhnikov-O-A"
},
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-M-R"
},
{
"family_name": "Williams",
"given_name": "James C., Jr.",
"clpid": "Williams-J-C-Jr"
},
{
"family_name": "Cleveland",
"given_name": "Robin O.",
"clpid": "Cleveland-R-O"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Crum",
"given_name": "Lawrence A.",
"clpid": "Crum-L-A"
},
{
"family_name": "Evan",
"given_name": "Andrew P.",
"clpid": "Evan-A-P"
},
{
"family_name": "McAteer",
"given_name": "James A.",
"clpid": "McAteer-J-A"
}
],
"abstract": "Background and Purpose: There is strong evidence that cavitation bubble activity contributes to stone breakage and that shockwave-bubble interactions are involved in the tissue trauma associated with shockwave lithotripsy. Cavitation control may thus be a way to improve lithotripsy. \n\nMaterials and Methods: High-speed photography was used to analyze cavitation bubble activity at the surface of artificial and natural kidney stones during exposure to lithotripter shockwaves in vitro. \n\nResults: Numerous individual bubbles formed on the surfaces of stones, but these bubbles did not remain independent but rather combined to form clusters. Bubble clusters formed at the proximal and distal ends and at the sides of stones. Each cluster collapsed to a narrow point of impact. Collapse of the proximal cluster eroded the leading face of the stone, and the collapse of clusters at the sides of stones appeared to contribute to the growth of cracks. Collapse of the distal cluster caused minimal damage. \n\nConclusion: Cavitation-mediated damage to stones is attributable, not to the action of solitary bubbles, but to the growth and collapse of bubble clusters.",
"doi": "10.1089/089277903769013568",
"pmcid": "PMC2442573",
"issn": "1557-900X",
"publisher": "Mary Ann Leibert",
"publication": "Journal of Endourology",
"publication_date": "2003-09",
"series_number": "7",
"volume": "17",
"issue": "7",
"pages": "435-446"
},
{
"id": "authors:ypx61-vnr37",
"collection": "authors",
"collection_id": "ypx61-vnr37",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126872",
"type": "conference_item",
"title": "An Algorithm for the Recovery of 2- and 3-D BiGlobal Instabilities of Compressible Flow Over 2-D Open Cavities",
"author": [
{
"family_name": "Theofilis",
"given_name": "V.",
"clpid": "Theofilis-V"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "The identification of numerical residuals from direct numerical simulations (DNS) with the least-damped BiGlobal eigenmodes of an underlying steady-state permits extraction of both the steady-state and amplitude functions of the BiGlobal eigenmodes from simple algebraic operations. Algorithms for the calculation of the basic state and the spatial structure of the related BiGlobal eigenmodes from transient DNS data have been constructed and presented.\n\nHere we extend initial calculations for the (closed) incompressible lid-driven cavity to the related (compressible) open-cavity flow. Order-of-magnitude savings are demonstrated when using of the discussed algorithm for the calculation of the basic state, compared with straightforward time-integration of the equations of motion until convergence in time. Further, employing this algorithm, different classes of instabilities in the open cavity are unified in the framework of BiGlobal instability analysis.",
"doi": "10.2514/6.2003-4143",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2003-06"
},
{
"id": "authors:ttbjb-5ef11",
"collection": "authors",
"collection_id": "ttbjb-5ef11",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165127116",
"type": "conference_item",
"title": "Inverse Technique for Vortex Imaging and Its Application to Feedback Flow Control",
"author": [
{
"family_name": "Suzuki",
"given_name": "Takao",
"clpid": "Suzuki-Takao"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "MacMartin",
"given_name": "Douglas G.",
"orcid": "0000-0003-1987-9417",
"clpid": "MacMartin-D-G"
}
],
"abstract": "A simple vortex imaging algorithm using a least square method is proposed for feedback flow control. The position and the circulation of a vortex convected in a channel are identified from the time history of pressure at a limited number of points on the wall. The capabilities of the algorithm are demonstrated using two-dimensional direct numerical simulations. A few observer points on one side of the wall are sufficient to detect the position and the circulation of a compact vortex to a reasonable degree of accuracy. This inverse algorithm is introduced to feedback separation control for a diffuser flow. The algorithm is modified for a curved channel, and the so-called \"estimator-corrector\" and \"fast algorithm\" are applied to reduce the uncertainty of prediction with less computational time. The DNS results demonstrate that the feedback control using the inverse technique can enhance the robustness against unsteady disturbances and lessen stagnation pressure loss.",
"doi": "10.2514/6.2003-4260",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2003-06"
},
{
"id": "authors:10ec8-7j479",
"collection": "authors",
"collection_id": "10ec8-7j479",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165128014",
"type": "conference_item",
"title": "A Study of the Role of Organized Structures in Jet Noise Generation",
"author": [
{
"family_name": "Reba",
"given_name": "R.",
"clpid": "Reba-R-A"
},
{
"family_name": "Narayanan",
"given_name": "S.",
"clpid": "Narayanan-S"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Dunlop",
"given_name": "M. J.",
"clpid": "Dunlop-M-J"
}
],
"abstract": "We present analytical, experimental and computational studies aimed at understanding the role of large-scale, organized structures in noise generation from high-speed, compressible jets. Two-point near-field pressure data from experiments are analyzed and used to identify parameters in a wave-packet based model for noise generation from organized, large-scale structures. The statistical spectrum of far field pressure is expressed in terms of two-point space-time correlations of the near-field pressure on a surface enclosing the jet. The surface is assumed to be sufficiently near the turbulent region tobe dominated by non-propagating hydrodynamic disturbances, yet sufficiently far such that linear behavior can be assumed in extending the near-field pressure to the far field. Validity of such assumptions is investigated by interrogating the jet DNS database of Freund [J. Fluid Mech. 438:277-305 2001]. The DNS data analysis is also used to investigate the impact of limited spatial resolution in the experiments. The analytical model is used to study far field noise generation from organized structures. Results show that, for sufficiently short structure lifetime, aft angle far field pressure spectra tend to exhibit frequency scaling with Helmholtz number, rather than Strouhal number.",
"doi": "10.2514/6.2003-3314",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2003-05"
},
{
"id": "authors:zejsc-4v390",
"collection": "authors",
"collection_id": "zejsc-4v390",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125289",
"type": "conference_item",
"title": "On the Noise Generated by Shear-Layer Instabilities in Turbulent Jets",
"author": [
{
"family_name": "Bertolotti",
"given_name": "Fabio P.",
"clpid": "Bertolotti-F-P"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Solutions to the linearized equations of motion are used to study sound radiation by convected disturbances in the jet core. The spectrum of eigenmodes reveals the presence of modes that represent convected vortical and entropic motions in the potential core of the jet. We investigate the near-field acoustics produced by these core modes using the Parabolozied Stability Equations. At the conditions of commercial jet engines during take-off, the core modes radiate sound effectively along Mach lines due to the jet centerline velocity being supersonic relative to the fee-stream speed of sound. Summing three of these modes to create two distinct disturbances - one that is velocity dominated, and another that is entropy dominated - one observes that entropy variations radiate sound more effectively than vortical variations. \n\nThe results yield a first insight into the impact of large-scale mixing inhomogeneities on the acoustic field. Such disturbances are created by devices in the jet engine itself, such as flow mixers, turbine exit vanes, and combustion-chamber (i.e. pattern factors).",
"doi": "10.2514/6.2003-1062",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2003-01"
},
{
"id": "authors:pjbqf-bcj08",
"collection": "authors",
"collection_id": "pjbqf-bcj08",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165127428",
"type": "conference_item",
"title": "Large-Scale Unsteadiness in a Two-Dimensional Diffuser: Numerical Study Toward Active Separation Control",
"author": [
{
"family_name": "Suzuki",
"given_name": "Takao",
"clpid": "Suzuki-Takao"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "We develop a reduced order model for large-scale unsteadiness (vortex shedding) in a two-dimensional diffuser and study the mechanisms of active flow separation control. This model can estimate the vortex shedding frequency for inviscid flows by accounting for the accumulated vorticity flux in the diffuser. The model can also predict the stagnation pressure loss, which consists of two parts: A steady part corresponds to static pressure loss on the detached area, and an unsteady part is associated with vortex shedding. To validate this model, we perform direct numerical simulation (DNS) of compressible, laminar diffuser flows. The comparison between the model and DNS shows good agreement at various Mach numbers and area ratios of the diffuser in terms of vortex shedding time scale and stagnation pressure loss. To investigate the effects of periodic mass injection near the separation point, we also perform DNS over a wide range of the forcing frequency. The DNS results show that periodic mass injection can pinch off vortices with a smaller size; accordingly, their convective velocity is increased, absorption of circulation from the wall is enhanced, and the extent of the separated region is reduced. As a result, the stagnation pressure recovery, particularly the unsteady part, is substantially improved as predicted by the model.",
"doi": "10.2514/6.2003-1138",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2003-01"
},
{
"id": "authors:w3btx-2kq60",
"collection": "authors",
"collection_id": "w3btx-2kq60",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-123721078",
"type": "book_section",
"title": "On the choice of norm for modeling compressible flow dynamics at reduced-order using the POD",
"book_title": "Proceedings of the 41st IEEE Conference on Decision and Control",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Rowley",
"given_name": "Clancy W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Freund",
"given_name": "Jonathan B.",
"clpid": "Freund-J-B"
},
{
"family_name": "Murray",
"given_name": "Richard M.",
"orcid": "0000-0002-5785-7481",
"clpid": "Murray-R-M"
}
],
"abstract": "We use POD (proper orthogonal decomposition)/Galerkin projection to investigate and derive reduced-order models of the dynamics of compressible flows. We examine DNS data for two flows, a turbulent M=0.9 jet and self-sustained oscillations in the flow over an open cavity, and show how different choices of norm lead to different definitions of the energetic structures, and, for the cavity, to different reduced-order models of the dynamics. For the jet, we show that the near-field dynamics are fairly well represented by relatively few modes, but that key processes of interest, such as acoustic radiation, are not well captured by norms that are defined based on volume integrals of pressure and velocity. For the cavity flow, we demonstrate that vector-valued POD modes lead to reduced-order models that are much more effective (accurate and stable) than scalar-valued modes defined independently for different flow variables.",
"doi": "10.1109/CDC.2002.1184376",
"isbn": "0-7803-7516-5",
"publisher": "IEEE",
"place_of_publication": "Piscataway, NJ",
"publication_date": "2002-12",
"pages": "3273-3278"
},
{
"id": "authors:thx55-z3525",
"collection": "authors",
"collection_id": "thx55-z3525",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059532",
"type": "conference_item",
"title": "Numerical Simulation of Shock and Bubble Dynamics in Shockwave Lithotripsy",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Tanguay",
"given_name": "Michel",
"clpid": "Tanguay-M"
}
],
"abstract": "Theoretical evaluation of the efficacy of stone comminution (and potential for tissue damage) during shockwave lithotripsy requires knowledge of the complex stress fields associated with both the incident focussing shock and the dynamics of cavitation bubbles that it induces. While simple models from geometrical acoustics and subsequent modeling of spherical bubbles in isolation (Gilmore equation) can provide estimates, high\u2010speed photography in vitro reveals a far more complex flow with bubble number densities that are sufficiently high such that collective effects associated with a cloud of bubbles are important. This talk will describe a modeling effort aimed at estimating stresses from these complex lithotripter generated flow fields. We compute the time\u2010dependent, compressible, ensemble\u2010averaged two\u2010phase flow equations with a finite\u2010difference scheme. Detailed modeling of the dynamics of bubbles (on the microscale) and high\u2010order weighted essentially nonoscillatory shock\u2010capturing schemes are employed. The model is compared to hydrophone and passive cavitation detection measurements, as well as qualitative comparison with high\u2010speed photography. Finally, we explore collective bubble mechanisms ranging from defocusing and shielding of the stone (for high bubble densities in the focal region) to enhanced stresses due to concerted cloud collapse in a dual\u2010pulse lithotripsy configuration.",
"doi": "10.1121/1.4779204",
"publication_date": "2002-10-25"
},
{
"id": "authors:sbjcv-sdt76",
"collection": "authors",
"collection_id": "sbjcv-sdt76",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-081643851",
"type": "article",
"title": "A Super-Grid-Scale Model for Simulating Compressible Flow on Unbounded Domains",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Ran",
"given_name": "Hongyu",
"clpid": "Ran-Hongyu"
}
],
"abstract": "A new buffer region (absorbing layer, sponge layer, fringe region) technique for computing compressible flows on unbounded domains is proposed. We exploit the connection between coordinate mapping from bounded to unbounded domains and filtering of the equations of motion in Fourier space in order to develop a model to damp flow disturbances (advective and acoustic) that propagate outside an arbitrarily defined near field. This effectively simulates a free-space boundary condition. Damping the solution in the far field is accomplished in a simple and effective way by applying a filter (similar to that used in large-eddy simulation) on a mesh in Fourier space, followed by a secondary filtering of the equations on the physical grid and implementation of a model for the unresolved scales. The final form of the buffer region is given in real space, independent of any discretization of the equations. Here we use a dealiased, Fourier spectral collocation method to demonstrate the efficacy of the buffer region for several model problems: acoustic wave propagation, convection of a finite-amplitude vortex, and a viscous starting jet in two dimensions. The results compare favorably to previous nonreflecting and absorbing boundary conditions.",
"doi": "10.1006/jcph.2002.7161",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2002-10-10",
"series_number": "1",
"volume": "182",
"issue": "1",
"pages": "191-212"
},
{
"id": "authors:tkjgt-qg954",
"collection": "authors",
"collection_id": "tkjgt-qg954",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:ELDjot02",
"type": "article",
"title": "A dilating vortex particle method for compressible flow",
"author": [
{
"family_name": "Eldredge",
"given_name": "Jeff D.",
"clpid": "Eldredge-J-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Leonard",
"given_name": "Anthony",
"clpid": "Leonard-A"
}
],
"abstract": "Vortex methods have become useful tools for the computation of incompressible fluid flow. In this work, a vortex particle method for the simulation of unsteady two-dimensional compressible flow is developed. By decomposing the velocity into irrotational and solenoidal parts, and using particles that are able to change volume and that carry vorticity, dilatation, enthalpy, entropy and density, the equations of motion are satisfied. Spatial derivatives are treated using the method of particle strength exchange with high-order-accurate, non-dissipative kernels. The new vortex method is applied to co-rotating and leapfrogging vortices in compressible flow, with the far acoustic field computed using a two-dimensional Kirchhoff surface.",
"issn": "1468-5248",
"publisher": "IOP",
"publication": "Journal of Turbulence",
"publication_date": "2002-09-20",
"series_number": "3",
"volume": "2002",
"issue": "3",
"pages": "Art. No. 036"
},
{
"id": "authors:3cj7q-41a41",
"collection": "authors",
"collection_id": "3cj7q-41a41",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092058511",
"type": "article",
"title": "An evaluation of linear instability waves as sources of sound in a supersonic turbulent jet",
"author": [
{
"family_name": "Mohseni",
"given_name": "Kamran",
"orcid": "0000-0002-1382-221X",
"clpid": "Mohseni-K"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Freund",
"given_name": "Jonathan B.",
"clpid": "Freund-J-B"
}
],
"abstract": "Mach wave radiation from supersonic jets is revisited to better quantify the extent to which linearized equations represent the details of the actual mechanism. To this end, we solve the linearized Navier\u2013Stokes equations (LNS) with precisely the same mean flow and inflow disturbances as a previous direct numerical simulation (DNS) of a perfectly expanded turbulent M = 1.92 jet [Freund et al., AIAA J. 38, 2023 (2000)]. We restrict our attention to the first two azimuthal modes, n = 0 and n = 1, which constitute most of the acoustic field. The direction of peak radiation and the peak Strouhal number matches the DNS reasonably well, which is in accord with previous experimental justification of the linear theory. However, it is found that the sound pressure level predicted by LNS is significantly lower than that from DNS. In order to investigate the discrepancy, individual frequency components of the solution are examined. These confirm that near the peak Strouhal number, particularly for the first helical mode n = 1, the amplification of disturbances in the LNS closely matches the DNS. However, away from the peak frequency (and generally for the azimuthal mode n = 0), modes in the LNS are damped while those in the DNS grow at rates comparable to those at the peak Strouhal number.",
"doi": "10.1063/1.1501545",
"issn": "1070-6631",
"publisher": "American Institute of Physics",
"publication": "Physics of Fluids",
"publication_date": "2002-09-05",
"series_number": "10",
"volume": "14",
"issue": "10",
"pages": "3593-3600"
},
{
"id": "authors:qp5x4-psg54",
"collection": "authors",
"collection_id": "qp5x4-psg54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100972",
"type": "conference_item",
"title": "Model-based control of cavity oscillations. II - System identification and analysis",
"author": [
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Murray",
"given_name": "Richard M.",
"orcid": "0000-0002-5785-7481",
"clpid": "Murray-R-M"
},
{
"family_name": "MacMartin",
"given_name": "Douglas G.",
"orcid": "0000-0003-1987-9417",
"clpid": "MacMartin-D-G"
},
{
"family_name": "Fabris",
"given_name": "Drazin",
"clpid": "Fabris-Drazin"
}
],
"abstract": "Experiments using active control to reduce oscillations in the flow past a rectangular cavity have uncovered surprising phenomena: in the controlled system, often new frequencies of oscillation appear, and often the main frequency of oscillation is split into two sideband frequencies. The goal of this paper is to explain these effects using physics-based models, and to use these ideas to guide control design.\n\nWe present a linear model for the cavity flow, based on the physical mechanisms of the familiar Rossiter model. Experimental data indicates that under many operating conditions, the oscillations are not self-sustained, but in fact are caused by amplification of external disturbances. We present some experimental results demonstrating the peak-splitting phenomena mentioned above, use the physics-based model to study the phenomena, and discuss fundamental performance limitations which limit the achievable performance of any control scheme.",
"doi": "10.2514/6.2002-972",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2002-08-22"
},
{
"id": "authors:t2g4t-tfa93",
"collection": "authors",
"collection_id": "t2g4t-tfa93",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059690",
"type": "conference_item",
"title": "POD Analysis of Sound Generation by a Turbulent Jet",
"author": [
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Freund",
"given_name": "J. B.",
"clpid": "Freund-J-B"
}
],
"abstract": "A Proper Orthogonal Decomposition (POD) is constructed for a Mach 0.9 turbulent jet using a well-validated direct numerical simulation database. Norms are defined based on near-field volume integrals of pressure, turbulence kinetic energy, streamwise velocity, and total enthalpy, two-dimensional integrals of streamswise velocity (to match experimental measurements), and far-field integrals of pressure over a sphere. We find substantially different POD modes for the different norms, and their efficiency at representing the full data is strongly dependent upon the norm and specifically which data we attempt to represent. To reproduce near-field turbulence statistics requires relatively few modes computed by a kinetic energy or pressure norm. However, a large number of the POD modes computed using a near-field norm are required to represent the sound field. The dominant near-field POD modes computed with either the near-field pressure norm or the sound field norm have the structure of wave packets.",
"doi": "10.2514/6.2002-72",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2002-08-22"
},
{
"id": "authors:tbabg-06308",
"collection": "authors",
"collection_id": "tbabg-06308",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190708-164305261",
"type": "article",
"title": "A General Deterministic Treatment of Derivatives in Particle Methods",
"author": [
{
"family_name": "Eldredge",
"given_name": "Jeff D.",
"clpid": "Eldredge-J-D"
},
{
"family_name": "Leonard",
"given_name": "Anthony",
"clpid": "Leonard-A"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "A unified approach to approximating spatial derivatives in particle methods using integral operators is presented. The approach is an extension of particle strength exchange, originally developed for treating the Laplacian in advection-diffusion problems. Kernels of high order of accuracy are constructed that can be used to approximate derivatives of any degree. A new treatment for computing derivatives near the edge of particle coverage is introduced, using \"one-sided\" integrals that only look for information where it is available. The use of these integral approximations in wave propagation applications is considered and their error is analyzed in this context using Fourier methods. Finally, simple tests are performed to demonstrate the characteristics of the treatment, including an assessment of the effects of particle dispersion, and their results are discussed.",
"doi": "10.1006/jcph.2002.7112",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2002-08-08",
"series_number": "2",
"volume": "180",
"issue": "2",
"pages": "686-709"
},
{
"id": "authors:jw299-fhy21",
"collection": "authors",
"collection_id": "jw299-fhy21",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:PREfedsm02",
"type": "conference_item",
"title": "A Reduced-Order Model of Heat Transfer Effects on the Dynamics of Bubbles",
"author": [
{
"family_name": "Preston",
"given_name": "A.",
"clpid": "Preston-A-T"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "C. E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "The Rayleigh-Plesset equation has been used extensively to model spherical bubble dynamics, yet it has been shown that it cannot correctly capture damping effects due to mass and thermal diffusion. Radial diffusion equations may be solved for a single bubble, but these are too computationally expensive to implement into a continuum model for bubbly cavitating flows since the diffusion equations must be solved at each position in the flow. The goal of the present research is to derive reduced-order models that account for thermal and mass diffusion. We present a model that can capture the damping effects of the diffusion processes in two ODE's, and gives better results than previous models.",
"publisher": "Caltech Library",
"publication_date": "2002-07-14"
},
{
"id": "authors:pyp8a-pv568",
"collection": "authors",
"collection_id": "pyp8a-pv568",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190708-164305134",
"type": "article",
"title": "A Vortex Particle Method for Two-Dimensional Compressible Flow",
"author": [
{
"family_name": "Eldredge",
"given_name": "Jeff D.",
"clpid": "Eldredge-J-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Leonard",
"given_name": "Anthony",
"clpid": "Leonard-A"
}
],
"abstract": "A vortex particle method is developed for simulating two-dimensional, unsteady compressible (low. The method uses the Helmholtz decomposition of the velocity field to separately treat the irrotational and solenoidal portions of the Now, and the particles are allowed to change volume to conserve mass. In addition to having vorticity and dilatation properties, the particles also carry density, enthalpy, and entropy. The resulting evolution equations contain terms that are computed with techniques used in some incompressible methods. Truncation of unbounded domains via a nonreflecting boundary condition is also considered. The fast multipole method is adapted to compressible particles in order to make the method computationally efficient. The new method is applied to several problems, including sound generation by corotating vortices and generation of vorticity by baroclinic torque.",
"doi": "10.1006/jcph.2002.7060",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2002-07-01",
"series_number": "2",
"volume": "179",
"issue": "2",
"pages": "371-399"
},
{
"id": "authors:bd1ek-16283",
"collection": "authors",
"collection_id": "bd1ek-16283",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059614",
"type": "book_section",
"title": "Reconstruction of large-scale structures and acoustic radiation from a turbulent M = 0.9 jet using proper orthogonal decomposition",
"book_title": "Advances in Turbulence IX: Proceedings of the Ninth European Turbulence Conference",
"author": [
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Freund",
"given_name": "J. B.",
"clpid": "Freund-J-B"
}
],
"contributor": [
{
"family_name": "Castro",
"given_name": "I. P."
},
{
"family_name": "Hancock",
"given_name": "P. E."
},
{
"family_name": "Thomas",
"given_name": "T. G."
}
],
"abstract": "The Proper Orthogonal Decomposition (POD) uses data to generate an optimal set of basis functions that represent the \"energy\" of the data, defined by a user-selected norm. This basis is optimal in the sense that a finite number of these modes represent more of the energy than any other set of orthogonal modes. The POD can be seen, on one hand, as a way to define energetic structures in a flow, essentially a generalization of the traditional Fourier-based spectrum to treat data that is inhomogeneous in one or more coordinate directions. But the POD modes are perhaps more useful in quantitatively modeling the dynamics of the flow, via Galerkin projection of the governing equations onto a relatively small number of modes in order to generate a reduced-order model.",
"isbn": "9788495999078",
"publisher": "International Center for Numerical Methods in Engineering (CIMNE)",
"place_of_publication": "Barcelona, Spain",
"publication_date": "2002-07",
"pages": "257-260"
},
{
"id": "authors:ecfj8-zwn42",
"collection": "authors",
"collection_id": "ecfj8-zwn42",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102590",
"type": "book_section",
"title": "Large Eddy Simulation of the Compressible Flow Over an Open Cavity",
"book_title": "ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. Volume 1: Fora, Parts A and B",
"author": [
{
"family_name": "Oh",
"given_name": "Keon-Je",
"clpid": "Oh-Keon-Je"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Large eddy simulation is used to investigate the compressible flow over a open cavity. The sub-grid scale stresses are modeled using the dynamic model. The compressible Navier-Stokes equations are solved with the sixth order accurate compact finite difference scheme in the space and the 4th order Runge-Kutta scheme in the time. The buffer zone techniques are used for non-reflecting boundary conditions. The results show a typical flow pattern of the shear layer mode of oscillation over the cavity. The votical disturbances, the roll-up of vorticity, and impingement and scattering of vorticity at the downstream cavity edge can be seen in the shear layer, while the flow inside the cavity is relatively quiescent. The predicted acoustic resonant frequencies are in good agreement with those of the empirical formula. The mean flow streamlines are nearly horizontal along the mouth of the cavity. The pressure has its minimum value in the vortex core inside the cavity. The variation of the model coefficient predicted by the dynamic model is quite large between 0 and 0.3. The model coefficient increases in the stream-wise evolution of the shear layer and sharply decreases near the wall due to the wall effect.",
"doi": "10.1115/FEDSM2002-31352",
"isbn": "0791836150",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "2002-07",
"pages": "1173-1178"
},
{
"id": "authors:aeb7v-9ss96",
"collection": "authors",
"collection_id": "aeb7v-9ss96",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100453",
"type": "book_section",
"title": "Numerical Investigation of Bubble Cloud Dynamics in Shock Wave Lithotripsy",
"book_title": "ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. Volume 1: Fora, Parts A and B",
"author": [
{
"family_name": "Tanguay",
"given_name": "Michel",
"clpid": "Tanguay-M"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "To provide greater understanding of some of the phenomena in Extracorporeal Shock Wave Lithotripsy (ESWL), we implemented a two-phase continuum model for cavitating flow and applied it to the simulation of bubble cloud dynamics in an electro-hydraulic lithotripter. Through the combination of a WENO shock capturing scheme, curvilinear coordinates system and ensemble averaged mixture model, we computed the evolution of the lithotripsy shock wave and the concomitant cavitation field. In this paper, we present the results for three different configurations: a single-pulse lithotripter (free field), a single-pulse lithotripter with rigid artificial kidney stone at the focal point, and a dual-pulse lithotripter. Qualitative and quantitative comparisons of the numerical results to experimental observations are also included.",
"doi": "10.1115/FEDSM2002-31010",
"isbn": "0791836150",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "2002-07",
"pages": "389-394"
},
{
"id": "authors:pqx7k-n4685",
"collection": "authors",
"collection_id": "pqx7k-n4685",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102208",
"type": "conference_item",
"title": "Cavitation bubble cluster activity in the breakage of stones by shock wave lithotripsy",
"author": [
{
"family_name": "Pishchalnikov",
"given_name": "Yuriy A.",
"clpid": "Pishchalnikov-Y-A"
},
{
"family_name": "Sapozhnikov",
"given_name": "Oleg A.",
"clpid": "Sapozhnikov-O-A"
},
{
"family_name": "Williams",
"given_name": "James C.",
"clpid": "Williams-J-C-Jr"
},
{
"family_name": "Evan",
"given_name": "Andrew P.",
"clpid": "Evan-A-P"
},
{
"family_name": "McAteer",
"given_name": "James A.",
"clpid": "McAteer-J-A"
},
{
"family_name": "Cleveland",
"given_name": "Robin O.",
"clpid": "Cleveland-R-O"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-M-R"
},
{
"family_name": "Crum",
"given_name": "Lawrence A.",
"clpid": "Crum-L-A"
}
],
"abstract": "High\u2010speed photography was used to investigate cavitation at the surface of artificial and natural kidney stones during exposure to lithotripter shock pulses in vitro. It was observed that numerous individual bubbles formed over virtually the entire surface of the stone, but these bubbles did not remain independent and combined with one another to form larger bubbles and bubble clusters. The movement of bubble boundaries across the surface left portions of the stone bubble free. The biggest cluster grew to envelop the proximal end of the stone (6.5 mm diameter artificial stone) then collapsed to a small spot that over multiple shots formed a crater in that face of the stone. The bubble clusters that developed at the sides of stones tended to align along fractures and to collapse into these cracks. High\u2010speed camera images demonstrated that cavitation\u2010mediated damage to stones was due not to the action of solitary, individual bubbles, but to the forceful collapse of dynamic clusters of bubbles.",
"doi": "10.1121/1.4778494",
"publication_date": "2002-05-06"
},
{
"id": "authors:1gt3e-gqy44",
"collection": "authors",
"collection_id": "1gt3e-gqy44",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102278",
"type": "article",
"title": "Cavitation Damage to Kidney Stones in SWL Involves the Action of Bubble Clusters: New Observations Using Ultra-High Speed Imaging in Vitro",
"author": [
{
"family_name": "Pishchalnikov",
"given_name": "Yuriy A.",
"clpid": "Pishchalnikov-Y-A"
},
{
"family_name": "Sapozhnikov",
"given_name": "Oleg A.",
"clpid": "Sapozhnikov-O-A"
},
{
"family_name": "Bailey",
"given_name": "Michael R.",
"clpid": "Bailey-M-R"
},
{
"family_name": "Williams",
"given_name": "James C.",
"clpid": "Williams-J-C-Jr"
},
{
"family_name": "Cleveland",
"given_name": "Robin O.",
"clpid": "Cleveland-R-O"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Crum",
"given_name": "Lawrence A.",
"clpid": "Crum-L-A"
},
{
"family_name": "Evan",
"given_name": "Andrew P.",
"clpid": "Evan-A-P"
},
{
"family_name": "McAteer",
"given_name": "James A.",
"clpid": "McAteer-J-A"
}
],
"abstract": "There is strong evidence io support the idea that cavitation plays a role in stone breakage in SWL. In order to better understand how cavitation bubbles interact with stones we recorded ultra-high speed movies of the bubble activity induced by single shock waves fired by an electrohydraulic lithotripter.",
"issn": "0022-5347",
"publisher": "Elsevier",
"publication": "Journal of Urology Supplement",
"publication_date": "2002-04",
"series_number": "4",
"volume": "167",
"issue": "4",
"pages": "S261-S262"
},
{
"id": "authors:jzmer-yr644",
"collection": "authors",
"collection_id": "jzmer-yr644",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:ROWjfm02",
"type": "article",
"title": "On self-sustained oscillations in two-dimensional compressible flow over rectangular cavities",
"author": [
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Basu",
"given_name": "Amit J.",
"clpid": "Basu-A-J"
}
],
"abstract": "Numerical simulations are used to investigate the resonant instabilities in two-dimensional flow past an open cavity. The compressible Navier\u2013Stokes equations are solved directly (no turbulence model) for cavities with laminar boundary layers upstream. The computational domain is large enough to directly resolve a portion of the radiated acoustic field, which is shown to be in good visual agreement with schlieren photographs from experiments at several different Mach numbers. The results show a transition from a shear-layer mode, primarily for shorter cavities and lower Mach numbers, to a wake mode for longer cavities and higher Mach numbers. The shear-layer mode is characterized well by the acoustic feedback process described by Rossiter (1964), and disturbances in the shear layer compare well with predictions based on linear stability analysis of the Kelvin\u2013Helmholtz mode. The wake mode is characterized instead by a large-scale vortex shedding with Strouhal number independent of Mach number. The wake mode oscillation is similar in many ways to that reported by Gharib & Roshko (1987) for incompressible flow with a laminar upstream boundary layer. Transition to wake mode occurs as the length and/or depth of the cavity becomes large compared to the upstream boundary-layer thickness, or as the Mach and/or Reynolds numbers are raised. Under these conditions, it is shown that the Kelvin\u2013Helmholtz instability grows to sufficient strength that a strong recirculating flow is induced in the cavity. The resulting mean flow is similar to wake profiles that are absolutely unstable, and absolute instability may provide an explanation of the hydrodynamic feedback mechanism that leads to wake mode. Predictive criteria for the onset of shear-layer oscillations (from steady flow) and for the transition to wake mode are developed based on linear theory for amplification rates in the shear layer, and a simple model for the acoustic efficiency of edge scattering.",
"doi": "10.1017/S0022112001007534",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2002-03-25",
"volume": "455",
"pages": "315-346"
},
{
"id": "authors:r6jj4-0v905",
"collection": "authors",
"collection_id": "r6jj4-0v905",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126408",
"type": "conference_item",
"title": "Model-based control of cavity oscillations. I - Experiments",
"author": [
{
"family_name": "Williams",
"given_name": "David R.",
"clpid": "Williams-D-R"
},
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Murray",
"given_name": "Richard M.",
"orcid": "0000-0002-5785-7481",
"clpid": "Murray-R-M"
},
{
"family_name": "MacMartin",
"given_name": "Douglas G.",
"orcid": "0000-0003-1987-9417",
"clpid": "MacMartin-D-G"
},
{
"family_name": "Fabris",
"given_name": "Drazin",
"clpid": "Fabris-Drazin"
},
{
"family_name": "Albertson",
"given_name": "Julie",
"clpid": "Albertson-Julie"
}
],
"abstract": "An experimental investigation of acoustic mode noise suppression was conducted in a cavity using a digital controller with a linear control algorithm. The control algorithm was based on flow field physics similar to the Rossiter model for acoustic resonance. Details of the controller and results from its implementation are presented in the companion paper by Rowley, et al.\n\nHere the experiments and some details of the flow field development are described, which were done primarily at Mach number 0.34 corresponding to single mode resonance in the cavity. A novel method using feedback control to suppress the resonant mode and open-loop forcing to inject a non-resonant mode was developed for system identification. The results were used to obtain empirical transfer functions of the components of resonance, and measurements of the shear layer growth for use in the design of the control algorithm.",
"doi": "10.2514/6.2002-971",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2002-01"
},
{
"id": "authors:26e04-3q183",
"collection": "authors",
"collection_id": "26e04-3q183",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:PREpf02",
"type": "article",
"title": "A Numerical Investigation of Unsteady Bubbly Cavitating Nozzle Flows",
"author": [
{
"family_name": "Preston",
"given_name": "A. T.",
"clpid": "Preston-A-T"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "C. E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "The effects of unsteady bubbly dynamics on cavitating flow through a converging-diverging nozzle are investigated numerically. A continuum model that couples the Rayleigh-Plesset equation with the continuity and momentum equations is used to formulate unsteady, quasi-one-dimensional partial differential equations. Flow regimes studied include those where steady-state solutions exist, and those where steady-state solutions diverge at the so-called flashing instability. these latter flows consist of unsteady bubbly shock waves traveling downstream in the diverging section of the nozzle. An approximate analytical expression is developed to predict the critical backpressure for choked flow. The results agree with previous barotropic models for those flows where bubbly dynamics are not important, but show that in many instances the neglect of bubbly dynamics cannot be justified. Finally the computations show reasonable agreement with an experiment that measures the spatial variation of pressure, velocity and void fraction for steady shockfree flows, and good agreement with an experiment that measures the throat pressure and shock position for flows with bubbly shocks. In the model, damping of the bubbly raidal motion is restricted to a simple \"effective\" viscosity, but many features of the flow are shown to be independent of the specific damping mechanism.",
"doi": "10.1063/1.1416497",
"issn": "1070-6631",
"publisher": "American Institute of Physics",
"publication": "Physics of Fluids",
"publication_date": "2002-01",
"series_number": "1",
"volume": "14",
"issue": "1",
"pages": "300-311"
},
{
"id": "authors:h85w1-x5r17",
"collection": "authors",
"collection_id": "h85w1-x5r17",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126719",
"type": "conference_item",
"title": "A unifying perspective of linear flow instabilities",
"author": [
{
"family_name": "Theofilis",
"given_name": "V.",
"clpid": "Theofilis-V"
},
{
"family_name": "Sherwin",
"given_name": "S. J.",
"clpid": "Sherwin-S-J"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"publisher": "Caltech Library",
"publication_date": "2002"
},
{
"id": "authors:3y6g3-xxv50",
"collection": "authors",
"collection_id": "3y6g3-xxv50",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104729692",
"type": "conference_item",
"title": "A Vortex Particle Method for Compressible Flows",
"author": [
{
"family_name": "Eldredge",
"given_name": "Jeff",
"clpid": "Eldredge-J-D"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Leonard",
"given_name": "Anthony",
"clpid": "Leonard-A"
}
],
"abstract": "A vortex particle method for the simulation of two-dimensional compressible flows is developed. The computational elements are Lagrangian particles that carry vorticity,dilatation,enthalpy,entropy and density. The velocity field is decomposed into irrotational and solenoidal parts,which allows its calculation in terms of the particles' vorticity and dilatation. The particle coverage is truncated and incident acoustic waves are absorbed using a suitable boundary treatment. A Kirchhoff surface formulation is developed for computing the far-field sound. The method is applied to a co-rotating vortex pair and the results are discussed.",
"doi": "10.2514/6.2001-2641",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2001-06"
},
{
"id": "authors:rs2a0-agd96",
"collection": "authors",
"collection_id": "rs2a0-agd96",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:PREcav01",
"type": "conference_item",
"title": "Toward Efficient Computation of Heat and Mass Transfer Effects in the Continuum Model for Bubbly Cavitating Flows",
"author": [
{
"family_name": "Preston",
"given_name": "Al",
"clpid": "Preston-A-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "Christopher E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "The Rayleigh-Plesset equation is used extensively to model spherical bubble dynamics, yet is has been shown that it cannot correctly capture damping effects due to mass and thermal diffusion. Full single bubble models have been successfully used to study these diffusion effects, but these are to computationally expensive to implement into the continuum model for bubbly cavitating flow since the diffusion equations must be solved in the radial direction at each position in the flow. The focus of the present research is the development of simpler and more efficient bubbly dynamic models that capture the important aspects of the diffusion processes. We present some preliminary results from a full bubbly model that has been developed to provide insight into possible simplifications. This in turn can be used to develop and validate simpler models. The full model is contrasted to the Rayleigh-Plesset equations, and a suggestion for possible improvement to the Rayleigh-Plesset equation is made.",
"publisher": "Caltech Library",
"publication_date": "2001-06"
},
{
"id": "authors:476q0-75d28",
"collection": "authors",
"collection_id": "476q0-75d28",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104731145",
"type": "conference_item",
"title": "Dynamical models for control of cavity oscillations",
"author": [
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Murray",
"given_name": "Richard M.",
"orcid": "0000-0002-5785-7481",
"clpid": "Murray-R-M"
}
],
"abstract": "We investigate nonlinear dynamical models for self-sustained oscillations in the flow past a rectangular cavity. The models are based on the method of Proper Orthogonal Decomposition (POD) and Galerkin projection, and we introduce an inner product and formulation of the equations of motion which enables one to use vector-valued POD modes for compressible flows. We obtain models between 3 and 20 states, which accurately describe both the short-time and long-time dynamics. This is a substantial improvement over previous models based on scalar-valued POD modes, which capture the dynamics for short time, but deviate for long time.",
"doi": "10.2514/6.2001-2126",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2001-05"
},
{
"id": "authors:trj71-n4y75",
"collection": "authors",
"collection_id": "trj71-n4y75",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104728798",
"type": "conference_item",
"title": "Computation of the Sources of Sound in Turbulent Flow",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Direct numerical simulations of turbulent flows and their radiated acoustic fields offer a detailed description of the acoustic sources at low Reynolds number. High Reynolds number jets will remain inaccessible to direct computation for many years to come and there is thus a great need for good models of the acoustic sources. The low Reynolds number simulations can provide insight and data for such source modeling efforts. In this brief survey of research in this area issues that were anticipated in the research of Professor David Crighton for whom this session has been dedicated are discussed. These include the technical challenges that must be overcome in order to accurately compute aeroacoustic flows the modeling of acoustic sources in jets and mixing layers as wave packets and the scattering and refraction of sound by turbulence.",
"doi": "10.1121/1.4744852",
"publication_date": "2001-05"
},
{
"id": "authors:57se5-p6j06",
"collection": "authors",
"collection_id": "57se5-p6j06",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104731478",
"type": "conference_item",
"title": "On the Role of Nonlinearity in Mach Wave Radiation in a Mach = 1.92 Jet",
"author": [
{
"family_name": "Mohseni",
"given_name": "Kamran",
"orcid": "0000-0002-1382-221X",
"clpid": "Mohseni-K"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Freund",
"given_name": "Jonathan B.",
"clpid": "Freund-J-B"
}
],
"abstract": "Mach wave radiation in a turbulent fully expanded supersonic jet is revisited. Our goal is to determine the extent to which predictions for the radiated sound that are based on linearized analysis agree with solution of the full nonlinear equations. To this end, we solve the linearized Navier-Stokes equations (LNS) with precisely the same mean flow and inflow disturbances as a previous direct numerical simulation (DNS) of a turbulent M = 1.92 jet.1 We restrict our attention to the first two azimuthal modes, n = 0 and n = 1, which constitute most of the acoustic field. The direction of peak radiation and the peak Strouhal number matches the DNS reasonably well, which is in accord with previous experimental justification of the linear theory. However, it is found that the sound pressure level predicted by LNS is significantly lower than that from DNS. Thus, linear theory misses a substantial component of the noise. In order to investigate the discrepancy, the behavior of individual frequency components of the solution are examined. Near the peak Strouhal number, particularly for the azimuthal mode n = 1, the amplification of disturbances in the LNS closely matches those from the DNS data. However, away from the peak frequency (and generally for the azimuthal mode n = 0), the DNS data shows amplification rates roughly comparable to those at the peak Strouhal number, while those from the linear computations are damped.",
"doi": "10.2514/6.2001-377",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2001-01"
},
{
"id": "authors:vvney-2rv11",
"collection": "authors",
"collection_id": "vvney-2rv11",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730673",
"type": "conference_item",
"title": "An overview of simulation, modeling, and active control of flow/acoustic resonance in open cavities",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "An overview of some recent advances in simulation, modeling, and control of flow/acoustic resonance in flows over open cavities is provided. A wide variety of experiments utilizing differing actuator concepts, with both open and closed-loop control, have shown that significant attenuation of tones and broadband noise is possible. These are discussed in connection with recent advances in theoretical modeling and numerical simulation. Such work may ultimately provide accurate low-order models of cavity resonance that are suitable for robust and effective control over a wide range of flow conditions. Several areas that will require further advances in our understanding of the flow physics are highlighted.",
"doi": "10.2514/6.2001-76",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2001-01"
},
{
"id": "authors:gfe62-pb328",
"collection": "authors",
"collection_id": "gfe62-pb328",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:MOHjfm01",
"type": "article",
"title": "Numerical experiments on vortex ring formation",
"author": [
{
"family_name": "Mohseni",
"given_name": "Kamran",
"orcid": "0000-0002-1382-221X",
"clpid": "Mohseni-K"
},
{
"family_name": "Ran",
"given_name": "Hongyu",
"clpid": "Ran-Hongyu"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Numerical simulations are used to study the formation of vortex rings that are generated by applying a non-conservative force of long duration, simulating experimental vortex ring generation with large stroke ratio. For sufficiently long-duration forces, we investigate the extent to which properties of the leading vortex ring are invariant to the force distribution. The results confirm the existence of a universal 'formation number' defined by Gharib, Rambod & Shariff (1998), beyond which the leading vortex ring is separated from a trailing jet. We find that the formation process is governed by two non-dimensional parameters that are formed with three integrals of the motion (energy, circulation, and impulse) and the translation velocity of the leading vortex ring. Limiting values of the normalized energy and circulation of the leading vortex ring are found to be around 0.3 and 2.0, respectively, in agreement with the predictions of Mohseni & Gharib (1998). It is shown that under this normalization smaller variations in the circulation of the leading vortex ring are obtained than by scaling the circulation with parameters associated with the forcing. We show that by varying the spatial extent of the forcing or the forcing amplitude during the formation process, thicker rings with larger normalized circulation can be generated. Finally, the normalized energy and circulation of the leading vortex rings compare well with the same properties for vortices in the Norbury family with the same mean core radius.",
"doi": "10.1017/S0022112000003025",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "2001",
"volume": "430",
"pages": "267-282"
},
{
"id": "authors:dv11f-bt291",
"collection": "authors",
"collection_id": "dv11f-bt291",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:COLpf00",
"type": "article",
"title": "Acoustic Saturation in Bubbly Cavitating Flow Adjacent to an Oscillating Wall",
"author": [
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "d'Auria",
"given_name": "F.",
"clpid": "d'Auria-F"
},
{
"family_name": "Brennen",
"given_name": "C.E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "Bubbly cavitating flow generated by the normal oscillation of a wall bounding a semi-infinite domain of fluid is computed using a continuum two-phase flow model. Bubble dynamics are computed, on the microscale, using the Rayleigh-Plesset equation. A Lagrangian finite volume\nscheme and implicit adaptive time marching are employed to accurately resolve bubbly shock waves and other steep gradients in the flow. The one-dimensional, unsteady computations show that when the wall oscillation frequency is much smaller than the bubble natural frequency, the power radiated away from the wall is limited by an acoustic saturation effect (the radiated power becomes\nindependent of the amplitude of vibration), which is similar to that found in a pure gas. That is, for large enough vibration amplitude, nonlinear steepening of the generated waves leads to shocking of the wave train, and the dissipation associated with the jump conditions across each shock limits the radiated power. In the model, damping of the bubble volume oscillations is restricted to a simple \"effective\" viscosity. For wall oscillation frequency less than the bubble natural frequency, the saturation amplitude of the radiated field is nearly independent of any specific damping mechanism. Finally, implications for noise radiation from cavitating flows are discussed.",
"doi": "10.1063/1.1313561",
"issn": "1070-6631",
"publisher": "American Institute of Physics",
"publication": "Physics of Fluids",
"publication_date": "2000-11",
"series_number": "11",
"volume": "12",
"issue": "11",
"pages": "2752-2761"
},
{
"id": "authors:vwmha-e2379",
"collection": "authors",
"collection_id": "vwmha-e2379",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:PREfedsm00",
"type": "conference_item",
"title": "A Numerical Investigation of Unsteady Bubbly Cavitating Nozzle Flows",
"author": [
{
"family_name": "Preston",
"given_name": "Al",
"clpid": "Preston-A-T"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "Christopher E.",
"clpid": "Brennen-C-E"
}
],
"abstract": "The effects of unsteady bubble dynamics on cavitating flow through a converging-diverging nozzle are investigated numerically. A continuum model that couples the Rayleigh-Plesset equation with the continuity and momentum equations is used to formulate unsteady, quasi-one-dimensional partial differential equations. These equations are solved numerically using a Lagrangian finite volume method. Special formulations are used at the boundary cells to allow Eulerian boundary conditions to be specified. Flow regimes studied include those where steady state solutions exist, and those where steady state solutions diverge at the so-called flashing instability. These latter flows consist of unsteady bubbly shock waves travelling downstream in the diverging section of the nozzle. The computations show reasonable agreement with an experiment that measures the spatial variation of pressure, velocity and void fraction for steady shockfree flows, and good agreement with an experiment that measures the shock position and throat pressure for flows with bubbly shocks.",
"publisher": "Caltech Library",
"publication_date": "2000-06"
},
{
"id": "authors:n9cw0-6z661",
"collection": "authors",
"collection_id": "n9cw0-6z661",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104731320",
"type": "conference_item",
"title": "POD Based Models of Self-Sustained Oscillations in the Flow Past an Open Cavity",
"author": [
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Murray",
"given_name": "Richard M.",
"orcid": "0000-0002-5785-7481",
"clpid": "Murray-R-M"
}
],
"abstract": "The goal of this work is to provide accurate dynamical models of oscillations in the flow past a rectangular cavity, for the purpose of bifurcation analysis and control. We have performed an extensive set of direct numerical simulations which provide the data used to derive and evaluate the models. Based on the method of Proper Orthogonal Decomposition (POD) and Galerkin projection, we obtain low-order models (from 6 to 60 states) which capture the dynamics very accurately over a few periods of oscillation, but deviate for long time.",
"doi": "10.2514/6.2000-1969",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "2000-06"
},
{
"id": "authors:fekcd-0mg70",
"collection": "authors",
"collection_id": "fekcd-0mg70",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104729599",
"type": "article",
"title": "Quasi\u2010linear gradients for capillary liquid chromatography with mass and tandem mass spectrometry",
"author": [
{
"family_name": "Zhou",
"given_name": "Jie",
"clpid": "Zhou-J"
},
{
"family_name": "Rusnak",
"given_name": "Felicia",
"clpid": "Rusnak-F"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Hathaway",
"given_name": "Gary M.",
"clpid": "Hathaway-G"
}
],
"abstract": "Gradient elution, capillary liquid chromatography mass spectrometry was performed with linear, static gradients constructed by laminar flowing ten, 1.5 mu L volume steps of decreasing organic concentration into tubing of small internal diameter. Sample loading, gradient formation, and sample elution were accomplished entirely by means of a commercially available micro-autosampler and single-syringe drive pump. The procedure was simple, fast, stable, and reproducible. Essentially linear gradients were produced without the use of additional valves, mixers, pumps or software. It took less than 10 minutes to form a gradient and less than 30 minutes to construct the set of individual buffer vials. The gradients were shown to be stable to storage. One hour after forming, peak retention times were reproduced to +/-0.5%. Long-term retention time reproducibility was found to vary by +/-2%, Chromatographic resolution was comparable or superior to that obtained by gradient elution with conventional dynamic mixing and split how, The procedure was adapted with a 'peak parking' method which extended the time for generating peptide fragmentation data up to 10 minutes per peptide with the triple quadruple mass spectrometer, Using this technique, collision data were collected at the 25 femtomole level on nine of ten tryptic peptides in a single run.",
"doi": "10.1002/(SICI)1097-0231(20000331)14:6%3C432::AID-RCM886%3E3.0.CO;2-T",
"issn": "0951-4198",
"publisher": "Wiley",
"publication": "Rapid Communications in Mass Spectrometry",
"publication_date": "2000-03-15",
"series_number": "6",
"volume": "14",
"issue": "6",
"pages": "432-438"
},
{
"id": "authors:qddde-84t61",
"collection": "authors",
"collection_id": "qddde-84t61",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20170408-150651603",
"type": "article",
"title": "Application of Lighthill's Equation to a Mach 1.92 Turbulent Jet",
"author": [
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Freund",
"given_name": "J. B.",
"clpid": "Freund-J-B"
}
],
"abstract": "It has often been suggested that simulations of turbulent jets could provide the necessary sound source information for jet noise predictions via Lighthill's acoustic analogy. Such an application of Lighthill's equation is useful for two reasons. First, it provides a framework for identifying and modeling acoustic sources in a turbulent flow. Second, it may provide a less expensive means of computing the sound generated by turbulent flows because the flow equations would need to be computed only in the source region.",
"doi": "10.2514/2.966",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "2000-02",
"series_number": "2",
"volume": "38",
"issue": "2",
"pages": "368-370"
},
{
"id": "authors:ag9g2-5de13",
"collection": "authors",
"collection_id": "ag9g2-5de13",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104729508",
"type": "article",
"title": "Discretely Nonreflecting Boundary Conditions for Linear Hyperbolic Systems",
"author": [
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Many compressible flow and aeroacoustic computations rely on accurate nonreflecting or radiation boundary conditions. When the equations and boundary conditions are discretized using a finite-difference scheme, the dispersive nature of the discretized equations can lead to spurious numerical reflections not seen in the continuous boundary value problem. Here we construct discretely nonreflecting boundary conditions, which account for the particular finite-difference scheme used, and are designed to minimize these spurious numerical reflections. Stable boundary conditions that are local and nonreflecting to arbitrarily high order of accuracy are obtained, and test cases are presented for the linearized Euler equations. For the cases presented. reflections for a pressure pulse leaving the boundary are reduced by up to two orders of magnitude over typical ad hoc closures, and for a vorticity pulse, reflections are reduced by up to four orders of magnitude.",
"doi": "10.1006/jcph.1999.6383",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2000-01-20",
"series_number": "2",
"volume": "157",
"issue": "2",
"pages": "500-538"
},
{
"id": "authors:8bt2k-c4t50",
"collection": "authors",
"collection_id": "8bt2k-c4t50",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104731562",
"type": "article",
"title": "Numerical Treatment of Polar Coordinate Singularities",
"author": [
{
"family_name": "Mohseni",
"given_name": "Kamran",
"orcid": "0000-0002-1382-221X",
"clpid": "Mohseni-K"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "[no abstract]",
"doi": "10.1006/jcph.1999.6382",
"issn": "0021-9991",
"publisher": "Elsevier",
"publication": "Journal of Computational Physics",
"publication_date": "2000-01-20",
"series_number": "2",
"volume": "157",
"issue": "2",
"pages": "787-795"
},
{
"id": "authors:tmf91-jbj73",
"collection": "authors",
"collection_id": "tmf91-jbj73",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190214-124414387",
"type": "article",
"title": "Transition of Chaotic Flow in a Radially Heated Taylor-Couette System",
"author": [
{
"family_name": "Kedia",
"given_name": "R.",
"clpid": "Kedia-R"
},
{
"family_name": "Hunt",
"given_name": "M. L.",
"orcid": "0000-0001-5592-2334",
"clpid": "Hunt-M-L"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Numerical simulations have been performed to study the stability of heated, incompressible Taylor-Couette flow for a radius ratio of 0.7 and a Prandtl number of 0.7. As Gr is increased, the Taylor cell that has the same direction of circulation as the natural convection current increases in size and the counterrotating cell becomes smaller. The flow remains axisymmetric and the average heat transfer decreases with the increase in Gr. When the cylinder is impulsively heated, the counterrotating cell vanishes and n = 1 spiral is formed for Gr = 1000. This transition marks an increase in the heat transfer due to an increase in the radial velocity component of the fluid. By slowly varying the Grashof number, the simulations demonstrate the existence of a hysteresis loop. Two different stable states with same heat transfer are found to exist at the same Grashof number. A time-delay analysis of the radial velocity and the local heat transfer coefficient time is performed to determine the dimension at two Grashof numbers. For a fixed Reynolds number of 100, the two-dimensional projection of the reconstructed attractor shows a limit cycle for Gr = \u22121700. The limit cycle behavior disappears at Gr = \u22122100, and the reconstructed attractor becomes irregular. The attractor dimension increases to about 3.2 from a value of 1 for the limit cycle case; similar values were determined for both the local heat transfer and the local radial velocity, indicating that the dynamics of the temperature variations can be inferred from that of the velocity variations.",
"doi": "10.1115/1.2826018",
"issn": "0022-1481",
"publisher": "American Society of Mechanical Engineers",
"publication": "Journal of Heat Transfer",
"publication_date": "1999-08",
"series_number": "3",
"volume": "121",
"issue": "3",
"pages": "574-582"
},
{
"id": "authors:emfpy-s6r46",
"collection": "authors",
"collection_id": "emfpy-s6r46",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730500",
"type": "book_section",
"title": "Computation of Sound Generation and Flow/Acoustic Instabilities in the Flow Past an Open Cavity",
"book_title": "Proceedings of FEDSM99",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Basu",
"given_name": "Amit J.",
"clpid": "Basu-A-J"
},
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
}
],
"abstract": "The modes of oscillation and radiated acoustic fields of compressible flows over open cavities are investigated computationally. The compressible Navier-Stokes equations are solved directly (no turbulence model) for two dimensional open cavities with laminar boundary layers upstream. The computational domain is large enough to directly resolve a portion of the radiated acoustic field. The results show a bifurcation from a shear layer mode, for shorter cavities and lower Mach numbers, to a wake mode for longer cavities and higher Mach numbers. The shear layer mode is well characterized by Rossiter modes and these oscillations lead to intense upstream acoustic radiation dominated by a single frequency. The wake mode is characterized instead by a large-scale vortex shedding with Strouhal number nearly independent the Mach number. The vortex shedding causes the boundary layer to periodically separate upstream of the cavity. Acoustic radiation is more intense, with multiple frequencies present. The wake mode oscillation is similar to that reported by Gharib & Roshko (1987) for incompressible cavity flows with laminar upstream boundary layers.",
"isbn": "9780791819616",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "1999-07"
},
{
"id": "authors:c363f-5m005",
"collection": "authors",
"collection_id": "c363f-5m005",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730595",
"type": "conference_item",
"title": "Numerical investigation of the flow past a cavity",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Basu",
"given_name": "Amit J.",
"clpid": "Basu-A-J"
},
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
}
],
"abstract": "Numerical simulations are used to investigate the resonant instabilities in the flow past an open cavity. The compressible Navier-Stokes equations are solved directly (no turbulence model) for two-dimensional cavities with laminar boundary layers upstream. The computational domain is large enough to directly resolve a portion of the radiated acoustic field. The results show a transition from a shear layer mode, for shorter cavities and lower Mach numbers, to a wake mode for longer cavities and higher Mach numbers. The shear layer mode is well characterized by Rossiter modes. The wake mode is characterized instead by a large-scale vortex shedding with Strouhal number independent of the Mach number. The vortex shedding causes the boundary layer to periodically separate upstream of the cavity. The wake mode oscillation is similar to that reported by Gharib and Roshko (J. Fluid Mech., 177, 1987) for incompressible ow with a laminar upstream boundary layer. The results suggest that laminar separation upstream of the cavity edge is the cause of the transition to wake mode.",
"doi": "10.2514/6.1999-1912",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "1999-05"
},
{
"id": "authors:77968-z4137",
"collection": "authors",
"collection_id": "77968-z4137",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730754",
"type": "conference_item",
"title": "Direct numerical simulation of sound generation in turbulent shear flows",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Direct numerical simulations of turbulent shear flows and their radiated acoustic fields have provided new insights into the mechanisms of sound generation, as well as the efficacy and limitations of the acoustic analogy approach. At present, these computations are expensive, and limited to relatively low Reynolds number and canonical flows. The computational approach consists of using high\u2010order accurate numerical methods, together with accurate and robust nonreflecting and buffer\u2010zone boundary conditions. This talk will focus on the results of computations of sound generated in mixing layers, jets, and open cavity flows. The relationship between linear stability waves in the flow and the radiated acoustic field is examined, in the context of a forced subsonic mixing layer and a fully turbulent supersonic round jet. For the subsonic flow, the acoustic sources can be modeled as wave packets, which radiate a superdirective acoustic field. For the supersonic jet, the directly computed (i.e., nonlinear source) acoustic field is compared to predictions based on radiating stability waves. Finally, the flow/acoustic instabilities in the subsonic flow over an open cavity are examined, and control strategies for reducing the internal acoustic load are explored.",
"doi": "10.1121/1.425824",
"publication_date": "1999-01-25"
},
{
"id": "authors:scsks-hk971",
"collection": "authors",
"collection_id": "scsks-hk971",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:BRE22snh99",
"type": "book_section",
"title": "Cloud Cavitation Phenomena",
"book_title": "Twenty-Second Symposium on Naval Hydrodynamics",
"author": [
{
"family_name": "Brennen",
"given_name": "C.",
"clpid": "Brennen-C-E"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Wang",
"given_name": "Y.-C.",
"clpid": "Wang-Y-C"
},
{
"family_name": "Preston",
"given_name": "A.",
"clpid": "Preston-A-T"
}
],
"abstract": "This paper describes investigations of the dynamics and acoustics of clouds of cavitation bubbles. Recent experimental and computational findings show that the collapse of clouds of cavitating bubbles can involve the formation of bubbly shock waves and that the focussing of these shock waves is responsible for the enhanced noise and damage in cloud cavitation. The recent experiments and computations of Reisman et al. (1) complement the work begun by Morch and Kedrinskii and their co-workers (2,3,4) and demonstrate that the very large impulsive pressures generated in bubbly cloud cavitation are caused by shock waves generated by the collapse mechanics of the bubbly cavitating mixture. Here we describe computational investigations conducted to explore these and other phenomena in greater detail as part of an attempt to find ways of ameliorating the most destructive effect associated with cloud cavitation.\n\nUnderstanding such bubbly flow and shock wave processes is important because these flow structures propagate the noise and produce the impulsive loads on nearby solid surfaces in a cavitating flow. How these shocks are formed and propagate in the much more complex cloud geometry associated with cavitating foils, propeller or pump blades is presently not clear. However, the computational investigations reveal some specific mechanisms which may be active in the dynamics and acoustics of these more complex flows.",
"isbn": "0309065372",
"publisher": "National Academy Press",
"place_of_publication": "Washington, DC",
"publication_date": "1999",
"pages": "239-253"
},
{
"id": "authors:4mf66-2m871",
"collection": "authors",
"collection_id": "4mf66-2m871",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104731244",
"type": "conference_item",
"title": "Numerically nonreflecting boundary conditions for multidimensional aeroacoustic computations",
"author": [
{
"family_name": "Rowley",
"given_name": "Clarence W.",
"orcid": "0000-0002-9099-5739",
"clpid": "Rowley-C-W"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Many compressible flow and aeroacoustic computations rely on accurate nonreflecting or radiation boundary conditions. When the equations and boundary conditions are discretized using a finite- difference scheme, the dispersive nature of the discretized equations can lead to spurious numerical reflections not seen in the continuous boundary value problem. These reflections can lead to poor convergence to a stationary state, and can lead to self-forcing of flows. We have constructed numerically nonreflecting boundary conditions which account for the particular finite-difference scheme used, and are designed to minimize these spurious numerical reflections. These extend our earlier work on one- dimensional boundary conditions to the multidimensional case. Stable boundary conditions which are nonreflecting to arbitrarily high-order-of-accuracy are obtained. Various test cases are presented which show excellent results.",
"doi": "10.2514/6.1998-2220",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "1998-06"
},
{
"id": "authors:f4qvs-qak45",
"collection": "authors",
"collection_id": "f4qvs-qak45",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:COLfed98",
"type": "book_section",
"title": "Computation of Shock Waves in Cavitating Flows",
"book_title": "Proceedings Of The 1998 ASME Fluids Engineering Division Summer Meeting",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Brennen",
"given_name": "Christopher E.",
"clpid": "Brennen-C-E"
},
{
"family_name": "d'Auria",
"given_name": "Fabrizio",
"clpid": "d'Auria-F"
}
],
"abstract": "Realistic cavitating flows are dominated by a large number of interacting bubbles. These clouds of bubbles exhibit highly nonlinear behavior with sudden changes in void fraction. Because of the potential damage caused by the coherent collapse of bubble clouds, there is a need for effective numerical models to predict their behavior. This paper presents a newly developed computational methodology to solve a continuum model of bubbly cavitating flow in which a Lagrangian finite volume technique is used to accurately and efficiently track all flow variables in space and time. We also present results for the solution of a one-dimensional model problem, namely cavitating shock waves produced by the normal motion of a wall bounding a semi-infinite domain of fluid. The roles of wave steepening and damping mechanisms in the collapse of bubble clouds are highlighted.",
"isbn": "0791819507",
"publisher": "American Society of Mechanical Engineers",
"place_of_publication": "New York, NY",
"publication_date": "1998-06",
"pages": "1-9"
},
{
"id": "authors:wh4re-8ma30",
"collection": "authors",
"collection_id": "wh4re-8ma30",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104729403",
"type": "article",
"title": "Numerical Simulations of Heat Transfer in Taylor-Couette Flow",
"author": [
{
"family_name": "Kedia",
"given_name": "R.",
"clpid": "Kedia-R"
},
{
"family_name": "Hunt",
"given_name": "M. L.",
"orcid": "0000-0001-5592-2334",
"clpid": "Hunt-M-L"
},
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Numerical simulations have been performed to study the effects of the gravitational and the centrifugal potentials on the stability of heated, incompressible Taylor-Couette flow. The flow is confined between two differentially heated, concentric cylinders, and the inner cylinder is allowed to rotate. The Navier-Stokes equations and the coupled energy equation are solved using a spectral method. To validate the code, comparisons are made with existing linear stability analysis and with experiments. The code is used to calculate the local and average heat transfer coefficients for a fixed Reynolds number (Re = 100) and a range of Grashof numbers. The investigation is primarily restricted to radius ratios 0.5 and 0.7 for fluids with Prandtl number of about 0.7. The variation of the local coefficients of heat transfer on the cylinder surface is investigated, and maps showing different stable states of the flow are presented. Results are also presented in terms of the equivalent conductivity, and show that heat transfer decreases with Grashof number in axisymmetric Taylor vortex flow regime, and increases with Grashof number after the flow becomes nonaxisymmetric.",
"doi": "10.1115/1.2830066",
"issn": "0022-1481",
"publisher": "American Society of Mechanical Engineers",
"publication": "Journal of Heat Transfer",
"publication_date": "1998-02-01",
"series_number": "1",
"volume": "120",
"issue": "1",
"pages": "65-71"
},
{
"id": "authors:ndh7z-em264",
"collection": "authors",
"collection_id": "ndh7z-em264",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:CEBcav98",
"type": "conference_item",
"title": "Computing Shock Waves in Cloud Cavitation",
"author": [
{
"family_name": "Brennen",
"given_name": "Christopher E.",
"clpid": "Brennen-C-E"
},
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "d'Auria",
"given_name": "Fabrizio",
"clpid": "d'Auria-F"
}
],
"abstract": "This paper presents a numerical investigation of some of the phenomena involved in the nonlinear dynamics of a homogeneous bubbly mixture bounded by an oscillatory wall. This problem represents an idealization of the flow in a typical vibratory cavitation damage device. Results are presented showing that wave steepening and ultimately shock wave formation occur as the magnitude of the excitation increases. The propagation characteristics of the waves through the bubbly medium have also been studied. Strong pressure peaks of short duration, corresponding to the coherent collapse of the bubble clusters, are computed and accurately resolved, both in space and time. As the amplitude of the excitation is increased a series of period doubling bifurcations occurs. The nonlinear dynamics of the oscillating bubble cluster are observed to follow a subharmonic route to chaos.",
"publisher": "Caltech Library",
"publication_date": "1998"
},
{
"id": "authors:d19fp-g3k15",
"collection": "authors",
"collection_id": "d19fp-g3k15",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104729942",
"type": "book_section",
"title": "Evaluation of Noise Radiation Mechanisms in Turbulent Jets",
"author": [
{
"family_name": "Colonius",
"given_name": "T.",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Mohseni",
"given_name": "K.",
"orcid": "0000-0002-1382-221X",
"clpid": "Mohseni-K"
},
{
"family_name": "Freund",
"given_name": "J. B.",
"clpid": "Freund-J-B"
},
{
"family_name": "Lele",
"given_name": "S. K.",
"clpid": "Lele-S-K"
},
{
"family_name": "Moin",
"given_name": "P.",
"orcid": "0000-0002-0491-7065",
"clpid": "Moin-Parviz"
}
],
"abstract": "Data from the direct numerical simulation (DNS) of a turbulent, compressible (Mach = 1.92) jet has been analyzed to investigate the process of sound generation. The overall goals are to understand how the different scales of turbulence contribute to the acoustic field, and to understand the role that linear instability waves play in the noise produced by supersonic turbulent jets. Lighthill's acoustic analogy was used to predict the radiate sound from turbulent source terms computed from the DNS data. Preliminary computations (for the axisymmetric mode of the acoustic field) showgood agreement between the acoustic field determined from DNS and acoustic analogy. Further work is needed to refine the calculations and investigate the source terms. Work was also begun to test the validity of linear stability wave models of sound generation in supersonic jets. An adjoint-based method was developed to project the DNS data onto the most unstable linear stability mode at different streamwise positions. This will allow the evolution of the wave and its radiated acoustic field, determined by solving the linear equations, to be compared directly with the evolution of the near and far-field fluctuations in the DNS.",
"publisher": "Center for Turbulence Research",
"publication_date": "1998"
},
{
"id": "authors:xdd1q-1ph06",
"collection": "authors",
"collection_id": "xdd1q-1ph06",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104729015",
"type": "article",
"title": "Numerically Nonreflecting Boundary and Interface Conditions for Compressible Flow and Aeroacoustic Computations",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Accurate nonreflecting or radiation boundary conditions are important for effective computation of aeroacoustic and compressible flow problems. The performance of such boundary conditions is often degraded upon discretization of the equations with finite difference and time marching methods. In particular, poorly resolved, spurious sawtooth waves are generated at boundaries due to the dispersive nature of the finite difference approximation. These disturbances can lead to spurious self-sustained oscillations in the flow (self-forcing), poor convergence to steady state, and long time instability of the numerics. Exact discretely nonreflecting boundary closures (boundary conditions for a downwind artificial boundary and an upwind physical boundary) are derived by considering a one-dimensional hyperbolic equation discretized with finite difference schemes and Runge-Kutta time advancements. The current methodology leads to stable local finite difference-like boundary closures, which are nonreflecting to an essentially arbitrarily high order of accuracy. These conditions can also be applied at interfaces where there is a discontinuity in the wave speed (a shock) or where there is an abrupt change in the grid spacing. Compared to other boundary treatments, the present boundary and interface conditions can reduce spurious reflected energy in the computational domain by many orders of magnitude.",
"doi": "10.2514/2.235",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "1997-07",
"series_number": "7",
"volume": "35",
"issue": "7",
"pages": "1126-1133"
},
{
"id": "authors:n2nnq-xsr39",
"collection": "authors",
"collection_id": "n2nnq-xsr39",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:COLjfm97",
"type": "article",
"title": "Sound generation in a mixing layer",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
},
{
"family_name": "Moin",
"given_name": "Parviz",
"orcid": "0000-0002-0491-7065",
"clpid": "Moin-Parviz"
}
],
"abstract": "The sound generated by vortex pairing in a two-dimensional compressible mixing layer is investigated. Direct numerical simulations (DNS) of the Navier-Stokes equations are used to compute both the near-field region and a portion of the acoustic field. The acoustic analogy due to Lilley (1974) is also solved with acoustic sources determined from the near-field data of the DNS. It is shown that several commonly made simplifications to the acoustic sources can lead to erroneous predictions for the acoustic field. Predictions based on the quadrupole form of the source terms derived by Goldstein (1976a, 1984) are in excellent agreement with the acoustic field from the DNS. However, despite the low Mach number of the flow, the acoustic far field generated by the vortex pairings cannot be described by considering compact quadrupole sources. The acoustic sources have the form of modulated wave packets and the acoustic far field is described by a superdirective model (Crighton & Huerre 1990). The presence of flow-acoustic interactions in the computed source terms causes the acoustic field predicted by the acoustic analogy to be very sensitive to small changes in the description of the source.",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "1997-01-10",
"volume": "330",
"pages": "375-409"
},
{
"id": "authors:r5sat-9t240",
"collection": "authors",
"collection_id": "r5sat-9t240",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730993",
"type": "conference_item",
"title": "Numerically nonreflecting boundary and interface conditions",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "Accurate nonreflecting or radiation boundary conditions are important for effective computation of aeroacoustic and compressible flow problems. In the present work, exact 'discretely nonreflecting boundary closures are derived by considering a one dimensional hyperbolic equation discretized with finite difference schemes and Runge-Kutta time advancements. The current methodology leads to stable local finite-difference-like boundary closures which are nonreflecting to an essentially arbitrarily high order of accuracy. These conditions can also be applied at interfaces where there is a discontinuity in the wave speed or where there is an abrupt change in the grid spacing. compared to other boundary treatments, the present boundary and interface conditions can reduce spurious reflected energy in the computational domain by many orders of magnitude.",
"doi": "10.2514/6.1996-1661",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "1996-05"
},
{
"id": "authors:ewbg6-j9t46",
"collection": "authors",
"collection_id": "ewbg6-j9t46",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104731067",
"type": "article",
"title": "Aeroacoustics",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
}
],
"abstract": "[no abstract]",
"issn": "0740-722X",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication": "Aerospace America",
"publication_date": "1995-12",
"series_number": "12",
"volume": "33",
"issue": "12",
"pages": "8"
},
{
"id": "authors:a7hqa-d3188",
"collection": "authors",
"collection_id": "a7hqa-d3188",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730109",
"type": "book_section",
"title": "The Sound Generated by a Two-Dimensional Shear Layer: A Comparison of Direct Computations and Acoustic Analogies",
"book_title": "First Joint CEAS/AIAA Aeroacoustics Conference (16th AIAA Aeroacoustics Conference) Proceedings",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
},
{
"family_name": "Moin",
"given_name": "Parviz",
"orcid": "0000-0002-0491-7065",
"clpid": "Moin-Parviz"
}
],
"abstract": "The sound generated by vortex pairing in a two-dimensional mixing layer is studied by solving the Navier-Stokes equations (DNS) for the layer and a portion of its acoustic field, and by solving acoustic analogies with source terms determined from the DNS. Predictions for the acoustic field based on Lilley's equation are in excellent agreement with the DNS results giving detailed verification of Lilley's acoustic analogy for the first time. We show that parts of the full source term which arise when the left-hand-side of Lilley's equation is linearized should not be neglected solely because they are attributable to refraction and scattering, nor because they are proportional to the dilatation. Lilley's source, -2u_(i,j)u_(j,k)u_(k,i), appears to be mainly responsible for the overall directivity of the acoustic field produced by the vortex pairings, which is highly focused at shallow angles to the streamwise axis. Scattering of the waves by the flow appears also to be significant, causing the directivity to be more omnidirectional than the Lilley source alone would predict. We also show how small errors in determining the sources, especially those due to scattering, can sometimes lead to large errors in the predictions.",
"isbn": "9783922010852",
"publisher": "Deutsche Gesellschaft f\u00fcr Luft- und Raumfahrt",
"place_of_publication": "Bonn, Germany",
"publication_date": "1995-06"
},
{
"id": "authors:9p1ar-z7w60",
"collection": "authors",
"collection_id": "9p1ar-z7w60",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730264",
"type": "book_section",
"title": "The Sound Generated by a Two-Dimensional Shear Layer: The Far Field Directivity from Computations and Acoustic Analogies",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
},
{
"family_name": "Moin",
"given_name": "Parviz",
"orcid": "0000-0002-0491-7065",
"clpid": "Moin-Parviz"
}
],
"abstract": "The sound generated by vortex pairing in a two- dimensional mixing layer is studied by direct numerical simulation of the Navier-Stokes equations (DNS) for the layer and a portion of its acoustic field, and by solving Lilley's equation (with source terms determined from the DNS) for the entire acoustic field. Predictions for the acoustic field based on Lilley's equation are in good agreement with the DNS results. The radiated acoustic field at the pairing frequencies is highly directive and cannot be produced by point quadrupole sources. Instead, it is of the superdirective character considered by Crighton and Huerre (1990, J. Fluid Mech., 220), where the magnitude of the pressure varies like the exponential of the cosine of the angle between the observation point and the downstream axis. By making modifications to this basic directivity, we account, in part, for shear in the mean velocity and the convection of the acoustic waves by the different freestream velocities on either side of the layer, and obtain a good overall agreement between the theory and the computations.",
"publisher": "ASME",
"publication_date": "1995"
},
{
"id": "authors:t35gg-bna56",
"collection": "authors",
"collection_id": "t35gg-bna56",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104729111",
"type": "article",
"title": "The scattering of sound waves by a vortex: numerical simulations and analytical solutions",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
},
{
"family_name": "Moin",
"given_name": "Parviz",
"orcid": "0000-0002-0491-7065",
"clpid": "Moin-Parviz"
}
],
"abstract": "The scattering of plane sound waves by a vortex is investigated by solving the compressible Navier-Stokes equations numerically, and analytically with asymptotic expansions. Numerical errors associated with discretization and boundary conditions are made small by using high-order-accurate spatial differentiation and time marching schemes along with accurate non-reflecting boundary conditions. The accuracy of computations of flow fields with acoustic waves of amplitude five orders of magnitude smaller than the hydrodynamic fluctuations is directly verified. The properties of the scattered field are examined in detail. The results reveal inadequacies in previous vortex scattering theories when the circulation of the vortex is non-zero and refraction by the slowly decaying vortex flow field is important. Approximate analytical solutions that account for the refraction effect are developed and found to be in good agreement with the computations and experiments.",
"doi": "10.1017/S0022112094003514",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "1994-02-10",
"volume": "260",
"pages": "271-298"
},
{
"id": "authors:27xtm-nzx97",
"collection": "authors",
"collection_id": "27xtm-nzx97",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730351",
"type": "conference_item",
"title": "Direct computation of the sound generated by two-dimensional shear layer",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
},
{
"family_name": "Moin",
"given_name": "Parviz",
"orcid": "0000-0002-0491-7065",
"clpid": "Moin-Parviz"
}
],
"abstract": "The sound generated by a two dimensional shear layer is investigated by Direct Numerical Simulation (DNS) of the compressible Navier-Stokes equations. A high-order-accurate numerical scheme and non-reflecting boundary conditions are used to accurately compute both the near field hydrodynamics and the acoustic waves produced by the layer. The directly computed acoustic field shows that the acoustic waves which are generated at the fundamental frequency (most unstable mode), and its first two sub-harmonics, originate near the region where the instability wave at these frequencies saturate, i.e. the region where the layer rolls up into vortices for the fundamental frequency, and the first two Vortex pairings for the sub-harmonics. The sound generated by the pairings is most intense in the downstream direction, indicating a superdirective acoustic source.",
"doi": "10.2514/6.1993-4328",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "1993-10"
},
{
"id": "authors:tehjx-7wf54",
"collection": "authors",
"collection_id": "tehjx-7wf54",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104728916",
"type": "article",
"title": "Boundary Conditions for Direct Computation of Aerodynamic Sound Generation",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
},
{
"family_name": "Moin",
"given_name": "Parviz",
"orcid": "0000-0002-0491-7065",
"clpid": "Moin-Parviz"
}
],
"abstract": "Accurate computation of the far-field sound along with the near-field source terms associated with a free shear flow requires that the Navier-Stokes equations be solved using accurate numerical differentiation and time-marching schemes, with nonreflecting boundary conditions. Nonreflecting boundary conditions have been developed for two-dimensional linearized Euler equations by Giles. These conditions are modified for use with nonlinear Navier-Stokes computations of open flow problems. At an outflow, vortical structures are found to produce large reflections due to nonlinear effects; these reflection errors cannot be improved by increasing the accuracy of the linear boundary conditions. An exit zone just upstream of an outflow where disturbances are significantly attenuated through grid stretching and filtering is developed for use with the nonreflecting boundary conditions; reflections from vortical structures are decreased by 3 orders of magnitude. The accuracy and stability of the boundary conditions are investigated in several model flows that include sound radiation by an energy source in a uniformly sheared viscous flow, the propagation of vortices in a uniform flow, and the spatial evolution of a compressible mixing layer.",
"doi": "10.2514/3.11817",
"issn": "0001-1452",
"publisher": "AIAA",
"publication": "AIAA Journal",
"publication_date": "1993-09",
"series_number": "9",
"volume": "31",
"issue": "9",
"pages": "1574-1582"
},
{
"id": "authors:88peb-6qp96",
"collection": "authors",
"collection_id": "88peb-6qp96",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104729209",
"type": "article",
"title": "The free compressible viscous vortex",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
},
{
"family_name": "Moin",
"given_name": "Parviz",
"orcid": "0000-0002-0491-7065",
"clpid": "Moin-Parviz"
}
],
"abstract": "The effects of compressibility on free (unsteady) viscous heat-conducting vortices are investigated. Analytical solutions are found in the limit of large, but finite, Reynolds number, and small, but finite, Mach number. The analysis shows that the spreading of the vortex causes a radial flow. This flow is given by the solution of an ordinary differential equation (valid for any Mach number), which gives the dependence of the radial velocity on the tangential velocity, density, and temperature profiles of the vortex; estimates of the radial velocity found by solving this equation are found to be in good agreement with numerical solutions of the full equations. The experiments of Mandella (1987) also report a radial flow in the vortex, but their estimates are much larger than the analytical predictions, and it is found that the flow inferred from the experiments violates the Second Law of Thermodynamics for two-dimensional axisymmetric flow. It is speculated that three-dimensionality is the cause of this discrepancy. To obtain detailed analytical solutions, the equations for the viscous evolution are expanded in powers of Mach number, M. Solutions valid to O(M^2), are discussed for vortices with finite circulation. Two specific initial conditions - vortices with initially uniform entropy and with initially uniform density - are analysed in detail. It is shown that swirling axisymmetric compressible flows generate negative radial velocities far from the vortex core owing to viscous effects, regardless of the initial distributions of vorticity, density and entropy.",
"doi": "10.1017/S0022112091000708",
"issn": "0022-1120",
"publisher": "Cambridge University Press",
"publication": "Journal of Fluid Mechanics",
"publication_date": "1991-09",
"volume": "230",
"pages": "45-73"
},
{
"id": "authors:4p8y7-kyz35",
"collection": "authors",
"collection_id": "4p8y7-kyz35",
"cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730425",
"type": "conference_item",
"title": "Scattering of Sound Waves by a Compressible Vortex",
"author": [
{
"family_name": "Colonius",
"given_name": "Tim",
"orcid": "0000-0003-0326-3909",
"clpid": "Colonius-T"
},
{
"family_name": "Lele",
"given_name": "Sanjiva K.",
"clpid": "Lele-S-K"
},
{
"family_name": "Moin",
"given_name": "Parviz",
"orcid": "0000-0002-0491-7065",
"clpid": "Moin-Parviz"
}
],
"abstract": "Scattering of plane sound waves by a compressible vortex is investigated by direct computation of the 2-d Navier-Stokes equations. Non-reflecting boundary conditions are utilized, and their accuracy is established by comparing results on different sized domains. Scattered waves are directly measured from the computations. The resulting amplitude and directivity pattern of the scattered waves is discussed, and compared to various theoretical predictions. For compact vortices (zero circulation), the scattered waves directly computed are in good agreement with predictions based on an acoustic analogy. Strong scattering at about \u00b130\u00b0 from the direction of incident wave propagation is observed. Back scattering is an order of magnitude smaller than forward scattering. For vortices with finite circulation refraction of the sound by the mean flow field outside the vortex core is found to be important in determining the amplitude and directivity of the scattered wave field.",
"doi": "10.2514/6.1991-494",
"publisher": "American Institute of Aeronautics and Astronautics",
"publication_date": "1991-01"
}
]