Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session A25: Flow Control: General I |
Hide Abstracts |
Chair: Jesse Little, University of Arizona Room: 31A |
Sunday, November 18, 2012 8:00AM - 8:13AM |
A25.00001: Maximum-entropy principle as Galerkin modelling paradigm Bernd R. Noack, Robert K. Niven, Clarence W. Rowley We show how the empirical Galerkin method, leading e.g. to POD models, can be derived from maximum-entropy principles building on Noack \& Niven 2012 JFM. In particular, principles are proposed (1) for the Galerkin expansion, (2) for the Galerkin system identification, and (3) for the probability distribution of the attractor. Examples will illustrate the advantages of the entropic modelling paradigm. [Preview Abstract] |
Sunday, November 18, 2012 8:13AM - 8:26AM |
A25.00002: Optimal mode decomposition for unsteady and turbulent flows Andrew Wynn, David Pearson, Bharathram Ganapathisubramani, Paul Goulart A new method, which we refer to as Optimal Mode Decomposition (OMD), to identify a linear model for the evolution of a fluid flow is presented. The method enables an ensemble of snapshot data to be used to estimate the linear dynamics of a flow by identifying a low order subspace of the flow and constructing dynamics on that low order subspace. An iterative procedure is used to find the optimal combination of linear model and subspace that minimises the system residual error. The OMD method is shown to be a generalisation of Dynamic Mode Decomposition (DMD), in which the subspace is not optimised but rather fixed to be the one spanned by the POD modes. A comparison between OMD and DMD is made using both a synthetic waveform and an experimental data set. The OMD technique is shown to have lower residual errors than DMD and is shown on a synthetic waveform to provide more accurate estimates of the system eigenvalues. This new method can be used with experimental and numerical data to calculate the `optimal' low-order model with a user-defined rank that best captures the system dynamics of unsteady and turbulent flows. [Preview Abstract] |
Sunday, November 18, 2012 8:26AM - 8:39AM |
A25.00003: The Influence of Relative Humidity on Dielectric Barrier Discharge Plasma Flow Control Actuator Performance M. Wicks, F.O. Thomas, T.C. Corke, M. Patel Dielectric barrier discharge (DBD) plasma actuators possess numerous advantages for flow control applications and have been the focus of several previous studies. Most work has been performed in relatively pristine laboratory settings. In actual flow control applications, however, it is essential to assess the impact of various environmental influences on actuator performance. As a first effort toward assessing a broad range of environmental effects on DBD actuator performance, the influence of relative humidity (RH) is considered. Actuator performance is quantified by force balance measurements of reactive thrust while RH is systematically varied via an ultrasonic humidifier. The DBD plasma actuator assembly, force balance, and ultrasonic humidifier are all contained inside a large, closed test chamber instrumented with RH and temperature sensors in order to accurately estimate the average RH at the actuator. Measurements of DBD actuator thrust as a function of RH for several different applied voltage regimes and dielectric materials and thicknesses are presented. Based on these results, several important design recommendations are made. [Preview Abstract] |
Sunday, November 18, 2012 8:39AM - 8:52AM |
A25.00004: Turbine blade cooling using Coulomb repulsion Robert Breidenthal, Joseph Colannino, John Dees, David Goodson, Igor Krichtafovitch, Tracy Prevo Video photography and thermocouples reveal the effect of an electric field on the flow around a stationary, idealized turbine blade downstream of a combustor. The hot products of combustion naturally include positive ions. When the blade is an electrode and elevated to a positive potential, it tends to attract the free electrons and repel the positive ions. Due to their lower mass, the light electrons are rapidly swept toward the blade, while the positive ions are repelled. As they collide with the neutrals in the hot gas, the positive ions transfer their momentum so that a Coulomb body force is exerted on the hot gas. Cool, compressed air is injected out of the stationary blade near its leading edge to form a layer of film cooling. In contrast to the hot combustion products, the cool air is not ionized. At the interface between the hot gas and the cool air, the Coulomb repulsion force acts on the former but not the latter, analogous to gravity at a stratified interface. An effective Richardson number representing the ratio of potential to kinetic energy characterizes the topography of the interface. When the electric field is turned on, the repulsion of the hot gas from the idealized blade is evident in video recordings and thermocouple measurements. [Preview Abstract] |
Sunday, November 18, 2012 8:52AM - 9:05AM |
A25.00005: On Optimal Model Identification in Hydrodynamics Bartosz Protas, Vladislav Bukshtynov, Bernd Noack, Marek Morzynski This work is motivated by two classes of problems, namely, identification of temperature--dependent material properties in complex thermo--fluid phenomena and identification of inertial manifolds in reduced--order models of hydrodynamic instabilities. It is demonstrated that these two problems can be framed in terms of the reconstruction of constitutive relations and we propose a robust computational approach to solve such problems using an optimization formulation based on some measurements. A special property of this formulation is that the control variable is a function of the state (i.e., the dependent variable), rather than the independent variable, and the main novelty is that the constitutive relation is determined in a very general form with no a priori assumptions other than smoothness. The optimization problem is solved using a gradient--descent method in which the cost functional gradients exhibit structure quite different than in typical optimization problems for differential equations. As an application, the proposed identification technique will be used to determine corrections to well--known models such as the Landau equation and the mean--field model so that they capture more accurately the behavior of actual hydrodynamic systems. [Preview Abstract] |
Sunday, November 18, 2012 9:05AM - 9:18AM |
A25.00006: Global Model Reduction for Fluid-Structure System Mingjun Wei, Min Xu, Tao Yang There are many challenges in the numerical simulation of a problem involving fluid flow and moving solid structures, especially when fully-coupled motion is considered. The challenge becomes even greater when a reduced-order model is required for the purposes of control and optimization of such complex and coupled systems. Here, we first introduce a global formulation of fluid and solid in a uniform Eulerian framework, which works for both prescribed and coupled moving structures in fluid flow. Based on the same formulation, we propose then to have a global model reduction by applying POD/Galerkin projection on a uniform Eulerian description of fluid, structure and their interaction. Preliminary results are shown as the approach being applied to the cases with either prescribed or coupled motion. [Preview Abstract] |
Sunday, November 18, 2012 9:18AM - 9:31AM |
A25.00007: Mixing Layer Excitation by Dielectric Barrier Discharge Plasma Actuators Richard Ely, Jesse Little The response of a mixing layer with velocity ratio 0.28 to perturbations near the high-speed side ($U_{2}$=11 m/s, \textit{Re}$_{L}$ = 0.26 x 10$^{6})$ of its origin from dielectric barrier discharge plasma actuators is studied experimentally. Both alternating current (ac) and nanosecond (ns) pulse driven plasma are investigated in an effort to clarify the mechanisms associated with each technique as well as the more general physics associated with flow control via momentum-based versus thermal actuation. Ac-DBD plasma actuators, which function through electrohydrodynamic effects, are found to generate an increase in mixing layer momentum thickness that is strongly dependent on forcing frequency. Results are qualitatively similar to previous archival literature on the topic employing oscillating flaps. Ns-DBD plasma, which is believed to function through thermal effects, has no measureable influence on the mixing layer profile at similar forcing conditions. In the context of previous archival literature, these results suggest different physical mechanisms govern active control via ac- and ns-DBD plasma actuation and more generally, momentum versus thermal perturbations. Further investigation of these phenomena will be provided through variation of the boundary/mixing layer properties and forcing parameters in the context of spatially and temporally resolved experimental data. [Preview Abstract] |
Sunday, November 18, 2012 9:31AM - 9:44AM |
A25.00008: Passive control and sensitivity analysis of thermo-acoustic systems via adjoint equations Luca Magri, Matthew Juniper We take a technique developed for the analysis of hydrodynamic stability and adapt it to thermo-acoustic systems. We aim to determine how thermo-acoustic systems should be changed in order to extend their linearly stable region. This technique uses adjoint equations to calculate the system's sensitivity to feedback mechanisms and to changes in the base state. We investigate two thermo-acoustic systems: a Rijke tube 1) electrically heated by a hot wire and 2) heated by a compact diffusion flame. The calculation of the components of the structural sensitivity tensor reveals the passive control mechanism that has the strongest influence on both the growth rate and frequency of thermo-acoustic oscillations. We illustrate the base-state sensitivity by calculating the effects of tiny variations of the base-state parameters. The successful application of adjoint sensitivity analysis to thermo-acoustics opens up new possibilities for the passive control of thermo-acoustic oscillations by providing gradient information that can be combined with constrained optimization algorithms in order to reduce linear growth rates. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700