Conference Item records
https://feeds.library.caltech.edu/people/Rowley-C-W/conference_item.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 14:13:12 +0000Numerically nonreflecting boundary conditions for multidimensional aeroacoustic computations
https://resolver.caltech.edu/CaltechAUTHORS:20190726-104731244
Authors: {'items': [{'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: 1998
DOI: 10.2514/6.1998-2220
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.https://authors.library.caltech.edu/records/4mf66-2m871Numerical investigation of the flow past a cavity
https://resolver.caltech.edu/CaltechAUTHORS:20190726-104730595
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
DOI: 10.2514/6.1999-1912
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.https://authors.library.caltech.edu/records/c363f-5m005POD Based Models of Self-Sustained Oscillations in the Flow Past an Open Cavity
https://resolver.caltech.edu/CaltechAUTHORS:20190726-104731320
Authors: {'items': [{'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'}, {'id': 'Murray-R-M', 'name': {'family': 'Murray', 'given': 'Richard M.'}, 'orcid': '0000-0002-5785-7481'}]}
Year: 2000
DOI: 10.2514/6.2000-1969
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.https://authors.library.caltech.edu/records/n9cw0-6z661Dynamical models for control of cavity oscillations
https://resolver.caltech.edu/CaltechAUTHORS:20190726-104731145
Authors: {'items': [{'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'}, {'id': 'Murray-R-M', 'name': {'family': 'Murray', 'given': 'Richard M.'}, 'orcid': '0000-0002-5785-7481'}]}
Year: 2001
DOI: 10.2514/6.2001-2126
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.https://authors.library.caltech.edu/records/476q0-75d28Model-based control of cavity oscillations. I - Experiments
https://resolver.caltech.edu/CaltechAUTHORS:20190718-165126408
Authors: {'items': [{'id': 'Williams-D-R', 'name': {'family': 'Williams', 'given': 'David R.'}}, {'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'}, {'id': 'Murray-R-M', 'name': {'family': 'Murray', 'given': 'Richard M.'}, 'orcid': '0000-0002-5785-7481'}, {'id': 'MacMartin-D-G', 'name': {'family': 'MacMartin', 'given': 'Douglas G.'}, 'orcid': '0000-0003-1987-9417'}, {'id': 'Fabris-Drazin', 'name': {'family': 'Fabris', 'given': 'Drazin'}}, {'id': 'Albertson-Julie', 'name': {'family': 'Albertson', 'given': 'Julie'}}]}
Year: 2002
DOI: 10.2514/6.2002-971
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.
Here 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.https://authors.library.caltech.edu/records/r6jj4-0v905Model-based control of cavity oscillations. II - System identification and analysis
https://resolver.caltech.edu/CaltechAUTHORS:20190709-092100972
Authors: {'items': [{'id': 'Rowley-C-W', 'name': {'family': 'Rowley', 'given': 'Clarence W.'}, 'orcid': '0000-0002-9099-5739'}, {'id': 'Williams-D-R', 'name': {'family': 'Williams', 'given': 'David R.'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Murray-R-M', 'name': {'family': 'Murray', 'given': 'Richard M.'}, 'orcid': '0000-0002-5785-7481'}, {'id': 'MacMartin-D-G', 'name': {'family': 'MacMartin', 'given': 'Douglas G.'}, 'orcid': '0000-0003-1987-9417'}, {'id': 'Fabris-Drazin', 'name': {'family': 'Fabris', 'given': 'Drazin'}}]}
Year: 2002
DOI: 10.2514/6.2002-972
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.
We 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.https://authors.library.caltech.edu/records/qp5x4-psg54Unsteadiness in Flow over a Flat Plate at Angle-of-Attack at Low Reynolds Numbers
https://resolver.caltech.edu/CaltechAUTHORS:20190718-165127033
Authors: {'items': [{'id': 'Taira-Kunihiko', 'name': {'family': 'Taira', 'given': 'Kunihiko'}, 'orcid': '0000-0002-3762-8075'}, {'id': 'Dickson-W-B', 'name': {'family': 'Dickson', 'given': 'William B.'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Dickinson-M-H', 'name': {'family': 'Dickinson', 'given': 'Michael H.'}, 'orcid': '0000-0002-8587-9936'}, {'id': 'Rowley-C-W', 'name': {'family': 'Rowley', 'given': 'Clarence W.'}, 'orcid': '0000-0002-9099-5739'}]}
Year: 2007
DOI: 10.2514/6.2007-710
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.https://authors.library.caltech.edu/records/e5m7e-s3b33Low-Dimensional Models for Control of Leading-Edge Vortices: Equilibria and Linearized Models
https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125547
Authors: {'items': [{'id': 'Ahuja-Sunil', 'name': {'family': 'Ahuja', 'given': 'Sunil'}}, {'id': 'Rowley-C-W', 'name': {'family': 'Rowley', 'given': 'Clarence W.'}, 'orcid': '0000-0002-9099-5739'}, {'id': 'Kevrekidis-I-G', 'name': {'family': 'Kevrekidis', 'given': 'Ioannis G.'}}, {'id': 'Wei-Mingjun', 'name': {'family': 'Wei', 'given': 'Mingjun'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Tadmor-G', 'name': {'family': 'Tadmor', 'given': 'Gilead'}}]}
Year: 2007
DOI: 10.2514/6.2007-709
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.https://authors.library.caltech.edu/records/g50jc-hpg03Unsteady Aerodynamic Forces on Small-Scale Wings: Experiments, Simulations, and Models
https://resolver.caltech.edu/CaltechAUTHORS:20190718-165125978
Authors: {'items': [{'id': 'Brunton-S-L', 'name': {'family': 'Brunton', 'given': 'Steven L.'}}, {'id': 'Rowley-C-W', 'name': {'family': 'Rowley', 'given': 'Clarence W.'}, 'orcid': '0000-0002-9099-5739'}, {'id': 'Taira-Kunihiko', 'name': {'family': 'Taira', 'given': 'Kunihiko'}, 'orcid': '0000-0002-3762-8075'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Collins-Jesse', 'name': {'family': 'Collins', 'given': 'Jesse'}}, {'id': 'Williams-D-R', 'name': {'family': 'Williams', 'given': 'David R.'}}]}
Year: 2008
DOI: 10.2514/6.2008-520
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.https://authors.library.caltech.edu/records/d2d1q-h1w55Control of a Semi-Circular Planform Wing in a "Gusting" Unsteady Free Stream Flow II: Modeling and Feedback Design
https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320405
Authors: {'items': [{'id': 'Tadmor-G', 'name': {'family': 'Tadmor', 'given': 'Gilead'}}, {'id': 'Williams-D-R', 'name': {'family': 'Williams', 'given': 'David R.'}}, {'id': 'Collins-Jesse', 'name': {'family': 'Collins', 'given': 'Jesse'}}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}, {'id': 'Rowley-C-W', 'name': {'family': 'Rowley', 'given': 'Clarence W.'}, 'orcid': '0000-0002-9099-5739'}]}
Year: 2008
DOI: 10.2514/6.2008-3977
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.https://authors.library.caltech.edu/records/6h8ep-hra38Closed-Loop Control of Leading Edge Vorticity on a 3D Wing: Simulations and Low-Dimensional Models
https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320932
Authors: {'items': [{'id': 'Rowley-C-W', 'name': {'family': 'Rowley', 'given': 'Clarence W.'}, 'orcid': '0000-0002-9099-5739'}, {'id': 'Ahuja-Sunil', 'name': {'family': 'Ahuja', 'given': 'Sunil'}}, {'id': 'Taira-Kunihiko', 'name': {'family': 'Taira', 'given': 'Kunihiko'}, 'orcid': '0000-0002-3762-8075'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2008
DOI: 10.2514/6.2008-3981
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.https://authors.library.caltech.edu/records/v3r9s-ztr60Low Reynolds Number Wing Response to an Oscillating Freestream With and Without Feed Forward Control
https://resolver.caltech.edu/CaltechAUTHORS:20190717-102319638
Authors: {'items': [{'id': 'Williams-D', 'name': {'family': 'Williams', 'given': 'David'}}, {'id': 'Quach-V', 'name': {'family': 'Quach', 'given': 'Vien'}}, {'id': 'Kerstens-W', 'name': {'family': 'Kerstens', 'given': 'Wesley'}}, {'id': 'Buntain-S', 'name': {'family': 'Buntain', 'given': 'Seth'}}, {'id': 'Tadmor-G', 'name': {'family': 'Tadmor', 'given': 'Gilead'}}, {'id': 'Rowley-C-W', 'name': {'family': 'Rowley', 'given': 'Clarence'}, 'orcid': '0000-0002-9099-5739'}, {'id': 'Colonius-T', 'name': {'family': 'Colonius', 'given': 'Tim'}, 'orcid': '0000-0003-0326-3909'}]}
Year: 2009
DOI: 10.2514/6.2009-143
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 τ^+ = 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.https://authors.library.caltech.edu/records/pxaz0-anz31Feedback Control of High-Lift State for A Low-Aspect-Ratio Wing
https://resolver.caltech.edu/CaltechAUTHORS:20190717-102320131
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: 10.2514/6.2010-357
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.https://authors.library.caltech.edu/records/m7ghj-7ct15