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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 13:29:26 +0000The Sound Generated by a Two-Dimensional Shear Layer: The Far Field Directivity from Computations and Acoustic Analogies
https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730264
Authors: {'items': [{'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Lele-S-K', 'name': {'family': 'Lele', 'given': 'Sanjiva K.'}}, {'id': 'Moin-Parviz', 'name': {'family': 'Moin', 'given': 'Parviz'}, 'orcid': '0000-0002-0491-7065'}]}
Year: 1995
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.https://authors.library.caltech.edu/records/9p1ar-z7w60The Sound Generated by a Two-Dimensional Shear Layer: A Comparison of Direct Computations and Acoustic Analogies
https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730109
Authors: {'items': [{'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Lele-S-K', 'name': {'family': 'Lele', 'given': 'Sanjiva K.'}}, {'id': 'Moin-Parviz', 'name': {'family': 'Moin', 'given': 'Parviz'}, 'orcid': '0000-0002-0491-7065'}]}
Year: 1995
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.https://authors.library.caltech.edu/records/a7hqa-d3188Evaluation of Noise Radiation Mechanisms in Turbulent Jets
https://resolver.caltech.edu/CaltechAUTHORS:20190726-104729942
Authors: {'items': [{'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'T.'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Mohseni-K', 'name': {'family': 'Mohseni', 'given': 'K.'}, 'orcid': '0000-0002-1382-221X'}, {'id': 'Freund-J-B', 'name': {'family': 'Freund', 'given': 'J. B.'}}, {'id': 'Lele-S-K', 'name': {'family': 'Lele', 'given': 'S. K.'}}, {'id': 'Moin-Parviz', 'name': {'family': 'Moin', 'given': 'P.'}, 'orcid': '0000-0002-0491-7065'}]}
Year: 1998
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.https://authors.library.caltech.edu/records/d19fp-g3k15Computation of Shock Waves in Cavitating Flows
https://resolver.caltech.edu/CaltechAUTHORS:COLfed98
Authors: {'items': [{'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Brennen-C-E', 'name': {'family': 'Brennen', 'given': 'Christopher E.'}}, {'id': "d'Auria-F", 'name': {'family': "d'Auria", 'given': 'Fabrizio'}}]}
Year: 1998
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.https://authors.library.caltech.edu/records/f4qvs-qak45Cloud Cavitation Phenomena
https://resolver.caltech.edu/CaltechAUTHORS:BRE22snh99
Authors: {'items': [{'id': 'Brennen-C-E', 'name': {'family': 'Brennen', 'given': 'C.'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'T.'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Wang-Y-C', 'name': {'family': 'Wang', 'given': 'Y.-C.'}}, {'id': 'Preston-A-T', 'name': {'family': 'Preston', 'given': 'A.'}}]}
Year: 1999
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.
Understanding 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.https://authors.library.caltech.edu/records/scsks-hk971Computation of Sound Generation and Flow/Acoustic Instabilities in the Flow Past an Open Cavity
https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730500
Authors: {'items': [{'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Basu-A-J', 'name': {'family': 'Basu', 'given': 'Amit J.'}}, {'id': 'Rowley-C-W', 'name': {'family': 'Rowley', 'given': 'Clarence W.'}, 'orcid': '0000-0002-9099-5739'}]}
Year: 1999
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.https://authors.library.caltech.edu/records/emfpy-s6r46Reconstruction of large-scale structures and acoustic radiation from a turbulent M = 0.9 jet using proper orthogonal decomposition
https://resolver.caltech.edu/CaltechAUTHORS:20190709-092059614
Authors: {'items': [{'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'T.'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Freund-J-B', 'name': {'family': 'Freund', 'given': 'J. B.'}}]}
Year: 2002
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.https://authors.library.caltech.edu/records/bd1ek-16283Numerical Investigation of Bubble Cloud Dynamics in Shock Wave Lithotripsy
https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100453
Authors: {'items': [{'id': 'Tanguay-M', 'name': {'family': 'Tanguay', 'given': 'Michel'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2002
DOI: 10.1115/FEDSM2002-31010
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.https://authors.library.caltech.edu/records/aeb7v-9ss96Large Eddy Simulation of the Compressible Flow Over an Open Cavity
https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102590
Authors: {'items': [{'id': 'Oh-Keon-Je', 'name': {'family': 'Oh', 'given': 'Keon-Je'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2002
DOI: 10.1115/FEDSM2002-31352
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.https://authors.library.caltech.edu/records/ecfj8-zwn42On the choice of norm for modeling compressible flow dynamics at reduced-order using the POD
https://resolver.caltech.edu/CaltechAUTHORS:20190214-123721078
Authors: {'items': [{'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Rowley-C-W', 'name': {'family': 'Rowley', 'given': 'Clancy W.'}, 'orcid': '0000-0002-9099-5739'}, {'id': 'Freund-J-B', 'name': {'family': 'Freund', 'given': 'Jonathan B.'}}, {'id': 'Murray-R-M', 'name': {'family': 'Murray', 'given': 'Richard M.'}, 'orcid': '0000-0002-5785-7481'}]}
Year: 2002
DOI: 10.1109/CDC.2002.1184376
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.https://authors.library.caltech.edu/records/w3btx-2kq60Cavitation in shock wave lithotripsy: the critical role of bubble activity in stone breakage and kidney trauma
https://resolver.caltech.edu/CaltechAUTHORS:20190214-131110058
Authors: {'items': [{'id': 'Bailey-M-R', 'name': {'family': 'Bailey', 'given': 'Michael R.'}}, {'id': 'Cleveland-R-O', 'name': {'family': 'Cleveland', 'given': 'Robin O.'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Crum-L-A', 'name': {'family': 'Crum', 'given': 'Lawrence A.'}}, {'id': 'Evan-A-P', 'name': {'family': 'Evan', 'given': 'Andrew P.'}}, {'id': 'Lingeman-J-E', 'name': {'family': 'Lingeman', 'given': 'James E.'}}, {'id': 'McAteer-J-A', 'name': {'family': 'McAteer', 'given': 'James A.'}}, {'id': 'Sapozhnikov-O-A', 'name': {'family': 'Sapozhnikov', 'given': 'Oleg A.'}}, {'id': 'Williams-J-C-Jr', 'name': {'family': 'Williams', 'given': 'James C., Jr.'}}]}
Year: 2003
DOI: 10.1109/ultsym.2003.1293503
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% ± 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—based on the concept of cavitation control— have now been introduced.https://authors.library.caltech.edu/records/d1bjf-kac10Linear Stability Analysis of Chevron Jet Profiles
https://resolver.caltech.edu/CaltechAUTHORS:20190214-074713989
Authors: {'items': [{'id': 'Gudmundsson-K', 'name': {'family': 'Gudmundsson', 'given': 'Kristjan'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2006
DOI: 10.1115/FEDSM2006-98485
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.https://authors.library.caltech.edu/records/t39zw-5gz04Compressible Multicomponent Flow Calculations and Shock-Bubble Interaction
https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125634
Authors: {'items': [{'id': 'Johnsen-E', 'name': {'family': 'Johnsen', 'given': 'Eric'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2006
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.https://authors.library.caltech.edu/records/ghkwc-yh566Numerical study of the collapse of a bubble subjected to a lithotripter pulse
https://resolver.caltech.edu/CaltechAUTHORS:20100923-144204048
Authors: {'items': [{'id': 'Johnsen-E', 'name': {'family': 'Johnsen', 'given': 'Eric'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2007
DOI: 10.1063/1.2723596
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).https://authors.library.caltech.edu/records/zsnjw-pqj51Spatial Stability Analysis of Chevron Jet Profiles
https://resolver.caltech.edu/CaltechAUTHORS:20190214-081956579
Authors: {'items': [{'id': 'Gudmundsson-K', 'name': {'family': 'Gudmundsson', 'given': 'Kristjan'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2007
DOI: 10.2514/6.2007-3599
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
fast 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
differences 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
increased. 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
chevron jets is consistent with that of the instability modes of the turbulent, spreading mean flow.https://authors.library.caltech.edu/records/pne1h-27m31Non-spherical collapse of an air bubble subjected to a lithotripter pulse
https://resolver.caltech.edu/CaltechAUTHORS:20100810-092143228
Authors: {'items': [{'id': 'Johnsen-E', 'name': {'family': 'Johnsen', 'given': 'Eric'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Kreider-W', 'name': {'family': 'Kreider', 'given': 'Wayne'}}, {'id': 'Bailey-M-R', 'name': {'family': 'Bailey', 'given': 'Michael R.'}}]}
Year: 2008
DOI: 10.1115/IMECE2007-43156
In order to better understand the contribution of bubble collapse
to stone comminution in shockwave lithotripsy, the shockinduced
and Rayleigh collapse of a spherical air bubble is investigated
using numerical simulations, and the free-field collapse of
a cavitation bubble is studied experimentally. In shock-induced
collapse near a wall, it is found that the presence of the bubble
greatly amplifies the pressure recorded at the stone surface; the
functional dependence of the wall pressure on the initial standoff
distance and the amplitude are presented. In Rayleigh collapse
near a solid surface, the proximity of the wall retards the
flow and leads to a more prominent jet. Experiments show that
re-entrant jets form in the collapse of cavitation bubbles excited
by lithotripter shockwaves in a fashion comparable to previous
studies of collapse near a solid surface.https://authors.library.caltech.edu/records/thjxd-ev812Unsteady Lift Suppression with a Robust Closed Loop Controller
https://resolver.caltech.edu/CaltechAUTHORS:20190717-102317714
Authors: {'items': [{'id': 'Williams-D', 'name': {'family': 'Williams', 'given': 'David'}}, {'id': 'Kerstens-W', 'name': {'family': 'Kerstens', 'given': 'Wesley'}}, {'id': 'Pfeiffer-J', 'name': {'family': 'Pfeiffer', 'given': 'Jens'}}, {'id': 'King-R', 'name': {'family': 'King', 'given': 'Rudibert'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2010
DOI: 10.1007/978-3-642-11735-0_2
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 _∞ 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.https://authors.library.caltech.edu/records/swhx3-hqn46Optimized Waveforms for Feedback Control of Vortex Shedding
https://resolver.caltech.edu/CaltechAUTHORS:20110418-093737292
Authors: {'items': [{'id': 'Joe-Won-Tae', 'name': {'family': 'Joe', 'given': 'Won Tae'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'MacMartin-D-G', 'name': {'family': 'MacMynowski', 'given': 'Douglas G.'}, 'orcid': '0000-0003-1987-9417'}]}
Year: 2010
DOI: 10.1007/978-3-642-11735-0_25
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.https://authors.library.caltech.edu/records/7m4qg-zc506Lock-On to a High-Lift State with Oscillatory Forcing in a Three-Dimensional Wake Flow
https://resolver.caltech.edu/CaltechAUTHORS:20190214-083422063
Authors: {'items': [{'id': 'Taira-Kunihiko', 'name': {'family': 'Taira', 'given': 'Kunihiko'}, 'orcid': '0000-0002-3762-8075'}, {'id': 'Rowley-C-W', 'name': {'family': 'Rowley', 'given': 'Clarence W.'}, 'orcid': '0000-0002-9099-5739'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2010
DOI: 10.1007/978-3-642-11735-0_6
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.https://authors.library.caltech.edu/records/h606f-x2q76Towards Prediction and Control of Large Scale Turbulent Structure Supersonic Jet Noise
https://resolver.caltech.edu/CaltechAUTHORS:20190214-125448163
Authors: {'items': [{'id': 'Schlinker-R-H', 'name': {'family': 'Schlinker', 'given': 'Robert H.'}}, {'id': 'Reba-R-A', 'name': {'family': 'Reba', 'given': 'Ramons A.'}}, {'id': 'Simonich-J-C', 'name': {'family': 'Simonich', 'given': 'John C.'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Gudmundsson-K', 'name': {'family': 'Gudmundsson', 'given': 'Kristjan'}}, {'id': 'Ladeinde-F', 'name': {'family': 'Ladeinde', 'given': 'Foluso'}}]}
Year: 2010
DOI: 10.1115/gt2009-60300
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.https://authors.library.caltech.edu/records/t4v19-d0h03Unstructured Large Eddy Simulation Technology for Prediction and Control of Jet Noise
https://resolver.caltech.edu/CaltechAUTHORS:20190215-114821703
Authors: {'items': [{'id': 'Khalighi-Y', 'name': {'family': 'Khalighi', 'given': 'Yaser'}}, {'id': 'Ham-F', 'name': {'family': 'Ham', 'given': 'Frank'}}, {'id': 'Moin-Parviz', 'name': {'family': 'Moin', 'given': 'Parviz'}, 'orcid': '0000-0002-0491-7065'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Lele-S-K', 'name': {'family': 'Lele', 'given': 'Sanjiva K.'}}, {'id': 'Schlinker-R-H', 'name': {'family': 'Schlinker', 'given': 'Robert H.'}}, {'id': 'Reba-R-A', 'name': {'family': 'Reba', 'given': 'Ramons A.'}}, {'id': 'Simonich-J-C', 'name': {'family': 'Simonich', 'given': 'John'}}]}
Year: 2010
DOI: 10.1115/GT2010-22306
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.https://authors.library.caltech.edu/records/0aycy-d4x55Numerical Analysis of High Speed Droplet Impact
https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320850
Authors: {'items': [{'id': 'Sanada-Toshiyuki', 'name': {'family': 'Sanada', 'given': 'Toshiyuki'}}, {'id': 'Ando-Keita', 'name': {'family': 'Ando', 'given': 'Keita'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2010
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.https://authors.library.caltech.edu/records/2xk6c-70w27Damage Potential of the Shock-Induced Collapse of a Gas Bubble
https://resolver.caltech.edu/CaltechAUTHORS:20190717-102318132
Authors: {'items': [{'id': 'Johnsen-E', 'name': {'family': 'Johnsen', 'given': 'Eric'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Cleveland-R-O', 'name': {'family': 'Cleveland', 'given': 'Robin'}}]}
Year: 2011
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.https://authors.library.caltech.edu/records/sgx27-00r74Effects of Target Compliance on a High-Speed Droplet Impact
https://resolver.caltech.edu/CaltechAUTHORS:20190712-112320367
Authors: {'items': [{'id': 'Sanada-Toshiyuki', 'name': {'family': 'Sanada', 'given': 'Toshiyuki'}}, {'id': 'Ando-Keita', 'name': {'family': 'Ando', 'given': 'Keita'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2012
DOI: 10.4028/www.scientific.net/SSP.187.137
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.https://authors.library.caltech.edu/records/zep0t-v3004Investigation of a New Model for Bubbly Cavitating Flow
https://resolver.caltech.edu/CaltechAUTHORS:20190712-112321189
Authors: {'items': [{'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Fuster-D', 'name': {'family': 'Fuster', 'given': 'Daniel'}}]}
Year: 2012
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.https://authors.library.caltech.edu/records/jhk09-xsf32Shock Propagation in Polydisperse Bubbly Liquids
https://resolver.caltech.edu/CaltechAUTHORS:20130719-124326298
Authors: {'items': [{'id': 'Ando-Keita', 'name': {'family': 'Ando', 'given': 'Keita'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Brennen-C-E', 'name': {'family': 'Brennen', 'given': 'Christopher E.'}}]}
Year: 2013
DOI: 10.1007/978-3-642-34297-4_5
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–Plesset-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.https://authors.library.caltech.edu/records/3kaja-vga24Flow energy piezoelectric bimorph nozzle harvester
https://resolver.caltech.edu/CaltechAUTHORS:20180713-132555490
Authors: {'items': [{'id': 'Sherrit-Stewart', 'name': {'family': 'Sherrit', 'given': 'Stewart'}, 'orcid': '0000-0003-0656-4889'}, {'id': 'Lee-Hyeong-Jae', 'name': {'family': 'Lee', 'given': 'Hyeong Jae'}}, {'id': 'Walkemeyer-P', 'name': {'family': 'Walkemeyer', 'given': 'Phillip'}}, {'id': 'Hasenoehrl-J', 'name': {'family': 'Hasenoehrl', 'given': 'Jennifer'}}, {'id': 'Hall-J-L', 'name': {'family': 'Hall', 'given': 'Jeffrey L.'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Tosi-L-P', 'name': {'family': 'Tosi', 'given': 'Luis Phillipe'}, 'orcid': '0000-0002-0819-4765'}, {'id': 'Arrazola-A', 'name': {'family': 'Arrazola', 'given': 'Alvaro'}}, {'id': 'Kim-Namhyo', 'name': {'family': 'Kim', 'given': 'Namhyo'}}, {'id': 'Sun-Kai', 'name': {'family': 'Sun', 'given': 'Kai'}}, {'id': 'Corbett-G', 'name': {'family': 'Corbett', 'given': 'Gary'}}]}
Year: 2014
DOI: 10.1117/12.2045191
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.https://authors.library.caltech.edu/records/s7msa-vcs77Modeling intermittent wavepackets and their radiated sound in a turbulent jet
https://resolver.caltech.edu/CaltechAUTHORS:20190712-112320455
Authors: {'items': [{'id': 'Jordan-P', 'name': {'family': 'Jordan', 'given': 'P.'}, 'orcid': '0000-0001-8576-5587'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'T.'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Brès-G-A', 'name': {'family': 'Brès', 'given': 'G. A.'}, 'orcid': '0000-0003-2507-8659'}, {'id': 'Zhang-M', 'name': {'family': 'Zhang', 'given': 'M.'}}, {'id': 'Towne-A', 'name': {'family': 'Towne', 'given': 'A.'}, 'orcid': '0000-0002-7315-5375'}, {'id': 'Lele-S-K', 'name': {'family': 'Lele', 'given': 'S. K.'}}]}
Year: 2014
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.https://authors.library.caltech.edu/records/jp325-m9k37Large eddy simulation of a Mach 0.9 turbulent jet
https://resolver.caltech.edu/CaltechAUTHORS:20190712-112321468
Authors: {'items': [{'id': 'Brès-G-A', 'name': {'family': 'Brès', 'given': 'G. A.'}, 'orcid': '0000-0003-2507-8659'}, {'id': 'Jordan-P', 'name': {'family': 'Jordan', 'given': 'P.'}, 'orcid': '0000-0001-8576-5587'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'T.'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Le-Rallic-M', 'name': {'family': 'Le Rallic', 'given': 'M.'}}, {'id': 'Jaunet-V', 'name': {'family': 'Jaunet', 'given': 'V.'}}, {'id': 'Lele-S-K', 'name': {'family': 'Lele', 'given': 'S. K.'}}]}
Year: 2014
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).https://authors.library.caltech.edu/records/cwazm-0rb41The Effects of Shock Strength on Droplet Breakup
https://resolver.caltech.edu/CaltechAUTHORS:20170622-065228163
Authors: {'items': [{'id': 'Meng-Jomela-Chen-Chen', 'name': {'family': 'Meng', 'given': 'Jomela C.'}, 'orcid': '0000-0002-8966-2291'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2015
DOI: 10.1007/978-3-319-16838-8_120
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.https://authors.library.caltech.edu/records/yvnbp-8g870Simulation and Modeling of Turbulent Jet Noise
https://resolver.caltech.edu/CaltechAUTHORS:20190712-112321094
Authors: {'items': [{'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'T.'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Sinha-A', 'name': {'family': 'Sinha', 'given': 'A.'}, 'orcid': '0000-0002-7122-3549'}, {'id': 'Rodriguez-D-M', 'name': {'family': 'Rodriguez', 'given': 'D.'}}, {'id': 'Towne-A', 'name': {'family': 'Towne', 'given': 'A.'}, 'orcid': '0000-0002-7315-5375'}, {'id': 'Liu-J', 'name': {'family': 'Liu', 'given': 'J.'}}, {'id': 'Brès-G-A', 'name': {'family': 'Brès', 'given': 'G. A.'}, 'orcid': '0000-0003-2507-8659'}, {'id': 'Appelö-D', 'name': {'family': 'Appelö', 'given': 'D.'}}, {'id': 'Hagstrom-T', 'name': {'family': 'Hagstrom', 'given': 'T.'}}]}
Year: 2015
DOI: 10.1007/978-3-319-14448-1_38
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.https://authors.library.caltech.edu/records/xfnn3-wny16Fluid flow nozzle energy harvesters
https://resolver.caltech.edu/CaltechAUTHORS:20180713-131155883
Authors: {'items': [{'id': 'Sherrit-Stewart', 'name': {'family': 'Sherrit', 'given': 'Stewart'}, 'orcid': '0000-0003-0656-4889'}, {'id': 'Lee-Hyeong-Jae', 'name': {'family': 'Lee', 'given': 'Hyeong Jae'}}, {'id': 'Walkemeyer-P', 'name': {'family': 'Walkemeyer', 'given': 'Phillip'}}, {'id': 'Winn-Tyler', 'name': {'family': 'Winn', 'given': 'Tyler'}}, {'id': 'Tosi-L-P', 'name': {'family': 'Tosi', 'given': 'Luis Phillipe'}, 'orcid': '0000-0002-0819-4765'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2015
DOI: 10.1117/12.2084574
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.https://authors.library.caltech.edu/records/2rrzx-xp278Parbolized Stability Analysis of Jets Issuing from Serrated Nozzles
https://resolver.caltech.edu/CaltechAUTHORS:20190712-112322726
Authors: {'items': [{'id': 'Sinha-A', 'name': {'family': 'Sinha', 'given': 'Aniruddha'}, 'orcid': '0000-0002-7122-3549'}, {'id': 'Xia-Hao', 'name': {'family': 'Xia', 'given': 'Hao'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2015
DOI: 10.1007/978-3-662-48868-3_34
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.https://authors.library.caltech.edu/records/cctdc-7sk68Parabolized Stability Analysis of Jets Issuing from Serrated Nozzles
https://resolver.caltech.edu/CaltechAUTHORS:20160915-092423132
Authors: {'items': [{'id': 'Sinha-A', 'name': {'family': 'Sinha', 'given': 'Aniruddha'}, 'orcid': '0000-0002-7122-3549'}, {'id': 'Xia-Hao', 'name': {'family': 'Xia', 'given': 'Hao'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2015
DOI: 10.1007/978-3-662-48868-3_34
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.https://authors.library.caltech.edu/records/7r1r1-80262Design and experimental evaluation of flextensional-cantilever based piezoelectric transducers for flow energy harvesting
https://resolver.caltech.edu/CaltechAUTHORS:20180713-132011622
Authors: {'items': [{'id': 'Lee-Hyeong-Jae', 'name': {'family': 'Lee', 'given': 'Hyeong Jae'}}, {'id': 'Sherrit-Stewart', 'name': {'family': 'Sherrit', 'given': 'Stewart'}, 'orcid': '0000-0003-0656-4889'}, {'id': 'Tosi-L-P', 'name': {'family': 'Tosi', 'given': 'Luis Phillipe'}, 'orcid': '0000-0002-0819-4765'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2016
DOI: 10.1117/12.2219269
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.https://authors.library.caltech.edu/records/t4cn2-d7v25Leading Edge Vortex Development on Pitching and Surging Airfoils: A Study of Vertical Axis Wind Turbines
https://resolver.caltech.edu/CaltechAUTHORS:20161202-082406384
Authors: {'items': [{'id': 'Dunne-R', 'name': {'family': 'Dunne', 'given': 'Reeve'}}, {'id': 'Tsai-Hsieh-Chen', 'name': {'family': 'Tsai', 'given': 'Hsieh-Chen'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'McKeon-B-J', 'name': {'family': 'McKeon', 'given': 'Beverley J.'}, 'orcid': '0000-0003-4220-1583'}]}
Year: 2016
DOI: 10.1007/978-3-319-30602-5_71
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.https://authors.library.caltech.edu/records/3880g-c5e82Transient Cavitation in Pre-Filled Syringes During Autoinjector Actuation
https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100145
Authors: {'items': [{'id': 'Veilleux-J-C', 'name': {'family': 'Veilleux', 'given': 'Jean-Christophe'}, 'orcid': '0000-0002-5420-9411'}, {'id': 'Maeda-Kazuki', 'name': {'family': 'Maeda', 'given': 'Kazuki'}, 'orcid': '0000-0002-5729-6194'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Shepherd-J-E', 'name': {'family': 'Shepherd', 'given': 'Joseph E.'}, 'orcid': '0000-0003-3181-9310'}]}
Year: 2018
DOI: 10.1115/1.861851_ch203
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.https://authors.library.caltech.edu/records/pv7w5-gtm86Numerical Simulation of the Bubble Cloud Dynamics in an Ultrasound Field
https://resolver.caltech.edu/CaltechAUTHORS:20190709-092058933
Authors: {'items': [{'id': 'Maeda-Kazuki', 'name': {'family': 'Maeda', 'given': 'Kazuki'}, 'orcid': '0000-0002-5729-6194'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2018
DOI: 10.1115/1.861851_ch151
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.https://authors.library.caltech.edu/records/mpa35-ghp95Investigation of the Energy Shielding of Kidney Stones by Cavitation Bubble Clouds during Burst Wave Lithotripsy
https://resolver.caltech.edu/CaltechAUTHORS:20190709-092102914
Authors: {'items': [{'id': 'Maeda-Kazuki', 'name': {'family': 'Maeda', 'given': 'Kazuki'}, 'orcid': '0000-0002-5729-6194'}, {'id': 'Maxwell-A-D', 'name': {'family': 'Maxwell', 'given': 'Adam D.'}}, {'id': 'Kreider-W', 'name': {'family': 'Kreider', 'given': 'Wayne'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Bailey-M-R', 'name': {'family': 'Bailey', 'given': 'Michael R.'}}]}
Year: 2018
DOI: 10.1115/1.861851_ch119
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.https://authors.library.caltech.edu/records/52byp-d7r63An Equation-of-State Tabulation Approach for Injectors with Non-Condensable Gases: Development and Analysis
https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100057
Authors: {'items': [{'id': 'Bode-Mathis', 'name': {'family': 'Bode', 'given': 'Mathis'}}, {'id': 'Satcunanathan-Sutharsan', 'name': {'family': 'Satcunanathan', 'given': 'Sutharsan'}}, {'id': 'Maeda-Kazuki', 'name': {'family': 'Maeda', 'given': 'Kazuki'}, 'orcid': '0000-0002-5729-6194'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Pitsch-H', 'name': {'family': 'Pitsch', 'given': 'Heinz'}}]}
Year: 2018
DOI: 10.1115/1.861851_ch10
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.https://authors.library.caltech.edu/records/mfh2h-99748Resolvent-based jet noise models: a projection approach
https://resolver.caltech.edu/CaltechAUTHORS:20211008-210432594
Authors: {'items': [{'id': 'Pickering-Ethan-M', 'name': {'family': 'Pickering', 'given': 'Ethan M.'}, 'orcid': '0000-0002-4485-6359'}, {'id': 'Towne-Aaron', 'name': {'family': 'Towne', 'given': 'Aaron'}, 'orcid': '0000-0002-7315-5375'}, {'id': 'Jordan-Peter', 'name': {'family': 'Jordan', 'given': 'Peter'}, 'orcid': '0000-0001-8576-5587'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2020
DOI: 10.2514/6.2020-0999
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= [0−1], 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 ≤ 3. Results are presented for round, isothermal, Mach 1.5 and 0.9 jets.https://authors.library.caltech.edu/records/0rvr5-1p492Immersed Boundary Projection Methods
https://resolver.caltech.edu/CaltechAUTHORS:20200518-095000249
Authors: {'items': [{'id': 'Dorschner-Benedikt', 'name': {'family': 'Dorschner', 'given': 'Benedikt'}, 'orcid': '0000-0001-8926-7542'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2020
DOI: 10.1007/978-981-15-3940-4_1
Immersed boundary methods are an attractive alternative to body-fitted grids for complex geometries and fluid–structure 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–structure 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.https://authors.library.caltech.edu/records/wt2zm-26216Application of the One-Way Navier-Stokes (OWNS) Equations to Hypersonic Boundary Layers
https://resolver.caltech.edu/CaltechAUTHORS:20211008-210432471
Authors: {'items': [{'id': 'Kamal-Omar', 'name': {'family': 'Kamal', 'given': 'Omar'}}, {'id': 'Rigas-Georgios', 'name': {'family': 'Rigas', 'given': 'Georgios'}, 'orcid': '0000-0001-6692-6437'}, {'id': 'Lakebrink-Matthew-T', 'name': {'family': 'Lakebrink', 'given': 'Matthew T.'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2020
DOI: 10.2514/6.2020-2986
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.https://authors.library.caltech.edu/records/7e8pm-sw309Input/Output Analysis of Hypersonic Boundary Layers using the One-Way Navier-Stokes (OWNS) Equations
https://resolver.caltech.edu/CaltechAUTHORS:20211008-210434815
Authors: {'items': [{'id': 'Kamal-Omar', 'name': {'family': 'Kamal', 'given': 'Omar'}}, {'id': 'Rigas-Georgios', 'name': {'family': 'Rigas', 'given': 'Georgios'}, 'orcid': '0000-0001-6692-6437'}, {'id': 'Lakebrink-Matthew', 'name': {'family': 'Lakebrink', 'given': 'Matthew'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2021
DOI: 10.2514/6.2021-2827
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.https://authors.library.caltech.edu/records/mfnan-yt466Analysis of forced subsonic jets using spectral proper orthogonal decomposition and resolvent analysis
https://resolver.caltech.edu/CaltechAUTHORS:20211008-183534650
Authors: {'items': [{'id': 'Heidt-Liam', 'name': {'family': 'Heidt', 'given': 'Liam'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Nekkanti-Akhil', 'name': {'family': 'Nekkanti', 'given': 'Akhil'}, 'orcid': '0000-0002-2173-8704'}, {'id': 'Schmdit-Oliver', 'name': {'family': 'Schmdit', 'given': 'Oliver'}}, {'id': 'Maia-Igor', 'name': {'family': 'Maia', 'given': 'Igor'}}, {'id': 'Jordan-Peter', 'name': {'family': 'Jordan', 'given': 'Peter'}, 'orcid': '0000-0001-8576-5587'}]}
Year: 2021
DOI: 10.2514/6.2021-2108
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.https://authors.library.caltech.edu/records/c7gv7-fst22Boundary conditions for turbulence simulation
https://authors.library.caltech.edu/records/mr3c8-7n898
Authors: {'items': [{'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2023
DOI: 10.1016/b978-0-32-391144-3.00014-0
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<p>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.</p>
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