Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session KT: Flow Control |
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Chair: Thomas Bewley, University of California, San Diego Room: Hilton Chicago Stevens 5 |
Monday, November 21, 2005 4:10PM - 4:23PM |
KT.00001: Control of Incompressible Flows Atul Sharma, Beverley McKeon, Jonathan Morrison, David Limebeer The prior art in flow control has not explicitly addressed the nonlinearity in the incompressible Navier-Stokes equations and has hitherto not produced a control strategy with a proof of closed loop stability for the nonlinear plant. We will show that because of the particular structure of the nonlinearities in the Navier-Stokes equations, relaminarisation is achievable in principle with a linear controller. The required controller synthesis problem has been solved in the control literature, subject to standard assumptions of detectability and stabilisability. We present a procedure to generate a controller that guarantees return to laminar flow in a closed or periodic domain, from any flow state and the region of guaranteed stability is not confined to a neghbourhood of small perturbations around laminar flow. The consequence of this is that fully turbulent flow or any mechanism of transition is controlled. The control of a simple 2x2 example that demonstrates the pertinent features is presented. The ongoing work of application to canonical turbulent flows and transition will be addressed with the aim of producing the associated benefits of greatly reduced skin friction. [Preview Abstract] |
Monday, November 21, 2005 4:23PM - 4:36PM |
KT.00002: Nonlinear Gradient Preconditioning in Problems of Optimal Control and Estimation Bartosz Protas Optimal control and estimation of PDE systems usually results in ill--posed inverse problems which are typically solved using iterative methods of optimization. Their rate of convergence is determined by the conditioning of the problem which can be improved using suitable preconditioning techniques. In the case of optimization of PDE systems such preconditioners can be constructed by endowing the optimization space with an appropriate inner--product structure, and the preconditioned gradient is obtained by solving a linear boundary--value problem. In this study we investigate how this procedure can be extended to optimization in general Banach spaces without an inner--product structure. It is shown that such nonlinearly--preconditioned gradients can be obtained via solution of a nonlinear elliptic problem generalizing the familiar Laplace equation. To highlight the utility of such preconditioning techniques for solution of control and estimation problems for nonlinear PDEs we present computational examples obtained for the Kuramoto--Sivashinsky and Navier--Stokes equations. [Preview Abstract] |
Monday, November 21, 2005 4:36PM - 4:49PM |
KT.00003: On POD Galerkin modeling of turbulent shear flows using 'subgrid' turbulence representations Bernd R. Noack, Laurent Cordier, Pierre Comte, Gilead Tadmor Low-dimensional POD Galerkin models are developed from LES data of turbulent shear flows, including mixing layers and jets. The key enablers are 'subgrid' turbulence representations to account for unresolved fine-scale fluctuations in the POD. These auxiliary models improve the prediction horizon and long-term statistics. Different calibration techniques are employed to determine the 'subgrid' parameters, e.g.\ modal eddy viscosities (Rempfer 1991). These methods range from physical modal balance equation to mathematical optimal control strategies. [Preview Abstract] |
Monday, November 21, 2005 4:49PM - 5:02PM |
KT.00004: Active Control of High Speed and High Reynolds Number Jets via Plasma Actuators$^{\ast }$ Jin-Hwa Kim, Yurii Utkin, Igor Adamovich, Mo Samimy Localized arc filament plasma actuators developed at OSU are uniquely suited to force high speed and high Reynolds number jets and shear flows. The actuators have high bandwidth ranging from 0 to 200 kHz and high amplitude with prescribed duty cycle and phase. Eight of these actuators were distributed around the perimeter of an axisymmetric nozzle of 2.54 cm diameter and were used to force ideally expanded Mach 1.3 jet with a Reynolds number of about 1x10$^{6}$. Axisymmetirc, helical (with m=1,2, and 4), flapping, and m = $\pm $2 modes were used. The streamwise flow images showed that the jet column mode was forced most effectively around St$_{D}$ = 0.33, which is in line with what other researchers have found. At this Strouhal number, robust and periodic structures were generated. The effects of forcing amplitude were very limited. However, the effectiveness of forcing was strongly affected by forcing frequency and duty cycle. For all the modes of actuation, the optimum duty cycle was 5-15{\%}. Pitot pressure measurements along the jet centerline showed significantly reduced potential core for some forced cases, especially for the forcing frequency around St$_{D}$ = 0.33. From streamwise images and the centerline pitot data, it appeared that helical and flapping modes are best for mixing enhancement. $^{\ast }$Supported by NASA Glenn Research Center and OCAPP. [Preview Abstract] |
Monday, November 21, 2005 5:02PM - 5:15PM |
KT.00005: Bluff Body Flow Control Using Plasma Actuators Flint Thomas, Alexey Kozlov, Thomas Corke In this study, the use of single dielectric barrier discharge plasma actuators for the control of bluff body flow separation is investigated. In particular, surface mounted plasma actuators are used to reduce both drag and unsteady vortex shedding from circular cylinders in cross-flow. It is demonstrated that the plasma-induced surface blowing gives rise to a local Coanda effect that promotes the maintenance of flow attachment. Large reductions in vortex shedding and drag are demonstrated for Reynolds numbers $\sim $ 10$^{4}${\ldots}10$^{5}$. Both steady and unsteady plasma-induced surface blowing is explored. Results are presented from experiments involving both two and four surface mounted actuators. [Preview Abstract] |
Monday, November 21, 2005 5:15PM - 5:28PM |
KT.00006: Electric Circuit Model for a Single-dielectric Barrier Discharge Plasma Actuator Dimtri Orlov, Thomas Corke, Mehul Patel It has been shown previously that the lumped-element circuit model correctly describes the temporal behavior of the aerodynamic plasma actuator. To incorporate this model into the Navier-Stokes (N-S) solver, it was modified to include the spatial behavior of the discharge within the plasma. To model this, the single dielectric barrier discharge plasma actuator is represented as a network of electric circuit elements. The electric circuit consists of $N$ elementary subcircuits, each representing a small physical domain with finite width and length. Each subcircuit consists of an air capacitor, dielectric capacitor, plasma resistive element, and diodes with time-dependent properties that govern the presence of the plasma. The results of the simulation are compared to the experimental data of the plasma spatial distribution obtained with a photomultiplier tube. The obtained results are used to provide accurate time-dependent models of the actuator in N-S simulations as well as to optimize the actuator designs to enhance their flow control effectiveness. [Preview Abstract] |
Monday, November 21, 2005 5:28PM - 5:41PM |
KT.00007: Control of turbulent shear flow structure using Lorentz force actuators Maureen McCamley, Charles Henoch, Kenneth Breuer We present experimental results concerning the use of electro- hydrodynamic ``Lorentz Force'' actuators to affect the near- wall flow of a low Reynolds number fully turbulent channel flow. The actuators are used to induce an oscillatory motion near the surface, and their effect on the structure of the turbulent flow is measured using Particle Image Velocimetry. Previous results have shown that certain amplitude and frequency combinations are effective in suppressing the turbulent fluctuations, wall shear stress and Reynolds stresses. We extend these measurements with conditional sampling of velocity data and computation of two-point velocity correlations which indicate that the effect of forcing is to reduce the streamwise scale of the near-wall coherent structures and to sharply reduce the frequency of high- amplitude turbulence-producing ``bursts''. Measurements phase- locked to the forcing are also presented. Lastly, the relaxation of the controlled flow to its uncontrolled state following the removal of the actuation is discussed. [Preview Abstract] |
Monday, November 21, 2005 5:41PM - 5:54PM |
KT.00008: Suction and Blowing Boundary Layer Measurements on a Novel Micro-pump Equipped Wing Victor Maldonado, Luciano Castillo A NACA-4412 airfoil wing section is outfitted with a micro-fluidic pump capable of providing span-wise, leading edge suction and blowing. The experiment is performed in a water tunnel for several free- stream test velocities. The detailed unsteady flow physics of the micro-pump/ boundary layer interaction are explored via velocity profile measurements taken using a laser Doppler anemometer (LDA). Finally, a basis for comparison of the efficiency between this innovative micro-pump and other micro-fluidic devices like synthetic jets is formulated. We attempt to generate micro-pump equivalent synthetic jet performance parameters such as jet momentum coefficient to determine the feasibility of such a micro-pump in applications like flow control and boundary layer separation control. [Preview Abstract] |
Monday, November 21, 2005 5:54PM - 6:07PM |
KT.00009: Control of a Supercavity-Piercing Fin Justin Syrstad, Martin Wosnik, Gary Balas, Roger E.A. Arndt Supercavitation provides a means of significantly reducing the drag of an underwater vehicle, thus enabling a dramatic increase in maximum speed. The control of supercavitating vehicles poses unique challenges. Only small regions at the nose (cavitator) and on the afterbody (fins) are in contact with water. Unlike for a fully wetted vehicle, there is an absence of lift on the body. Viable vehicle control options are limited to actuation of the cavitator and fins, and possibly thrust vectoring. Fin control is highly nonlinear due to the interaction of the fin with the cavity wall. Also, the cavity-fin interaction exhibits strong hysteresis effects. Tests were conducted in the high-speed water tunnel at St. Anthony Falls Laboratory with a semi-axisymmetric, ventilated cavity and a single wedged-shaped, 45 degree swept, cavity-piercing fin. Using a variety of fin control experiments, cavity stability and hysteresis effects were studied and compared to theoretical results. Fin torque was measured for different angles of attack with varying cavitation numbers. A closed-loop control experiment with fin responses to upstream/cavity disturbances is being carried out. Simulink models are being used to control the experimental setup and the measured parameters (fin position and torque) are compared to theoretical results. [Preview Abstract] |
Monday, November 21, 2005 6:07PM - 6:20PM |
KT.00010: Recent progress in the estimation of laminar and turbulent wall-bounded flows Thomas Bewley, Bartosz Protas, Jerome Hoepffner, Mattias Chevalier, Dan Henningson, Paolo Luchini We present recent progress on a range of techniques to estimate the flow state based on a history of noisy measurements from an array of flush-mounted skin-friction and pressure sensors on a wall:\\ (A) {\bf Model predictive estimation} (a.k.a. 4D-var) in a ``{\bf multiscale retrograde}'' framework {\small (Bewley \& Protas, {\it Physica D} 2004)};\\ (B) {\bf Kalman filtering} based on an artificial (but sufficiently smooth) stochastic model for the covariance matrix characterizing the statistics of the state disturbance forcing {\small (Hoepffner {\it et al.}, {\it JFM} 2005)};\\ (C) {\bf Extended Kalman filtering} based on a covariance matrix derived from a DNS of a turbulent flow {\small (Chevalier {\it et al.}, {\it JFM} submitted)}; and\\ (D) {\bf Weiner filtering} derived from DNS-based impulse response functions. [Preview Abstract] |
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