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 H25: Flow Control: Internal flow |
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Chair: Michael Amitay, Rensselaer Polytechnic Institute Room: 31A |
Monday, November 19, 2012 10:30AM - 10:43AM |
H25.00001: Feedback stabilization of vortex flows in a finite-length straight pipe S. Wang, R. Gong, Z. Rusak, L. Xu, S. Taylor, L. Jeng The properties of a recently proposed\footnote{Rusak et al JFM 2012.} feedback stabilization method of swirling flows in a finite-length pipe are studied. In the natural case, when swirl is above a critical level, linearly unstable modes appear in sequence as swirl increases and evolve to a vortex breakdown state. Based on a long-wave approach, the feedback control methodology is shown to enforce decay of perturbation's kinetic energy and to quench all instability modes at above critical swirl. In the case of a solid-body rotation, the effectiveness of this control approach is further analyzed through a mode analysis of the full linearized flow control problem. We first establish the asymptotic decay of all modes with real growth rates. We then compute growth rates of all modes according to the linearized flow control problem for swirl up to 50\% above critical level. Flow stabilization in the whole swirl range is demonstrated. However, control effectiveness is sensitive to choice of the control gain. An inadequate gain, either insufficient or excessive, could lead to a failure of control at high swirl levels. Predictions of controlled flow cases agree with numerical simulations using the full unsteady and axisymmetric Euler equations with fluidic actuation along the pipe wall. [Preview Abstract] |
Monday, November 19, 2012 10:43AM - 10:56AM |
H25.00002: Design of Servo-Driven Actuators for Spanwise-Varying Control of a Backward-Facing Step Flow Marc Schostek, Lorenz Sigurdson For an experimental study of a forced backward-facing step water flow the design of 16 piston actuators was necessary. The 16 actuators connect to manifolds to force the flow at the step edge through many more actuation ports. The 16 actuators allowed for variant forcing in the spanwise direction with a resolution of 0.5 times the step height $h$. They are capable of producing unique perturbation waveforms of forcing velocity amplitudes $0~<~u'/U_\infty~\le~2$ and either single or multiple forcing Strouhal numbers in the range $0~<~St_h~\le~1.0$. These forcing amplitudes are larger than ever used in any previous forced backward-facing step flow experiments. The process of designing the servo-motor driven actuator system will be discussed. [Preview Abstract] |
Monday, November 19, 2012 10:56AM - 11:09AM |
H25.00003: High Amplitude Forcing Dependence of Control of a Backward-Facing Step Flow Lorenz Sigurdson, Marc Schostek An experimental study was conducted of a forced backward-facing step water flow, which required the design of 16 piston actuators. They allowed spanwise-varying forcing with a resolution of 0.5 times the step height h. They were capable of producing unique perturbation waveforms of forcing velocity amplitudes $0~<~u'/U_\infty~\le~2$, and forcing Strouhal numbers based on h in the range $0~<~St_h~\le~1.0$. These forcing amplitudes are larger than those used in known previous forced backward-facing step flow experiments. For measurement of the reattachment length a hydro-tuft was designed which indicated flow direction. A set of images taken of an array of tufts was processed to calculate a time-averaged reattachment line. Initial experiments were for spanwise-invariant forcing for the full amplitude range and forcing frequencies of $0~<~St_h~\le~0.5$. The results showed an optimal $St_h$ which shifted to a lower value with increasing forcing amplitude, and a non-monotonic shortening of the reattachment length. As a function of forcing amplitude, reattachment reached a pronounced local minimum at $u'/U_\infty~\approx~0.3-0.4$, and then rose to a local maxima at a $u'/U_\infty~\approx~0.5-0.6$. Larger forcing amplitudes caused even more shortening than the local minimum. [Preview Abstract] |
Monday, November 19, 2012 11:09AM - 11:22AM |
H25.00004: Feed-forward control of the flow over a backward-facing step Fabien Juillet, Peter Schmid, Beverley McKeon In this study, the control of incoming perturbations in convection-dominated flows is analyzed numerically and experimentally. For this purpose, multiple sensors and actuators are used. First, a model is built from input and output data sequences using a least-squares system identification. Then, a feed-forward Model Predicitive Controller (MPC) is designed. It appears that feed-forward control is particularly relevant when applied to convection-dominated flows. A very general and flexible formulation of the technique is introduced and validated on the flow over a backward-facing step. Although the objective sensors are localized on the walls, the impact of the control is more global and perturbations are also reduced in the middle of the channel. The coupling of system identification together with feed-forward control was found to be a flexible, efficient and experimentally feasible strategy. In particular, the successful numerical control is further supported by experimental results. Support from Ecole Polytechnique and the Partner University Fund (PUF) is gratefully acknowledged. [Preview Abstract] |
Monday, November 19, 2012 11:22AM - 11:35AM |
H25.00005: Experimental Investigation of Flow Control in a Compact Inlet Duct Brian Debronsky, Michael Amitay Attractive to aircraft designers are compact inlets, which implement curved flow paths from the air intake of the engine to the compressor face. A compromise must be made between the compactness of the inlet and its aerodynamic performance. The aerodynamic purpose of inlets is to decelerate the oncoming flow before reaching the engine while minimizing total pressure loss, unsteadiness and distortion. Low length-to-diameter ratio inlets have a high degree of curvature, which inevitably causes flow separation and secondary flows. To address this issue, active flow control was implemented on a compact (L/D = 1.6) inlet to improve its performance metrics. The experiments were conducted at a Mach number of 0.44, where the actuation from an array of skewed and pitched jets produced streamwise vortices opposite to the secondary flow structures. The actuation resulted in an improved pressure recovery at the aerodynamic interface plane (AIP), where both the strength of the secondary structures and the flow unsteadiness were significantly reduced. [Preview Abstract] |
Monday, November 19, 2012 11:35AM - 11:48AM |
H25.00006: The valveless impedance pump and the unexpected effect of convection in tight spaces James Woodcock, John Sader, Ivan Marusic The valveless impedance pump (VIP) consists of a thin tube, one section of which is elastic and is subjected to rhythmic pinching at some point offset from its centre. This induces travelling waves which propagate back and forth along an elastic section of a tube, which in turn induces a flow within the tube. We have investigated the physics underlying the VIP using a perturbation analysis and found that, contrary to expectations, convection plays an important role despite the thinness of the tube. Using numerical simulations, it has been shown that convection can in fact be the dominant mechanism at work within the flow if the oscillations of the tube are of sufficient amplitude. We propose that convection may generally play an important role, even within thin tubes and channels, where the velocity gradients along the wall are significant. [Preview Abstract] |
Monday, November 19, 2012 11:48AM - 12:01PM |
H25.00007: Transient Dynamics Modeling of Experimental Hypersonic Inlet Unstart Kelley E. Hutchins, Michael Szmuk, Noel T. Clemens, Maruthi R. Akella, Jeffrey M. Donbar, Sivaram Gogineni During unstart, the rapid upstream propagation of a hypersonic engine's inlet-isolator shock system can be readily detected through pressure measurements. Specifically, the magnitude of the pressure readings suddenly and dramatically increases as soon as the leading edge of the shock system passes the measurement location. In this work, attempts to model the transient dynamics governing shock motion have been made through the use of system identification techniques. The result of these efforts is a partially nonlinear dynamic model that describes shock motion through pressure signals. The process reveals the possibility of partitioning the nonlinear behaviors from the linear dynamics with relative ease. Related attempts are then made to create a model where the nonlinear portion has been pre-specified leaving only the linear portion to be determined by system identification. The modeling and identification process specific to the unstart data used is discussed, and successful models are presented for both the full system identification and the partitioned model cases. The suitability of various input data types is explored, and comments on practicality are made. [Preview Abstract] |
Monday, November 19, 2012 12:01PM - 12:14PM |
H25.00008: Closed-loop control of a turbulent mixing layer - experimental study Vladimir Parezanovic, Joel Delville, Carine Fourment, Laurent Cordier, Bernd Noack, Tamir Shaqarin Open and closed-loop control of a turbulent mixing layer is experimentally performed in a dedicated wind-tunnel facility (TUCOROM). The flow is manipulated with 100 independently operating fluidic micro-valve actuators integrated transversely in the trailing edge of the splitter plate. Sensing is performed with a rake of 30 hot-wire probes located downstream in the mixing layer. The control goal is a manipulation of the spreading rate. The underlying physical mechanisms employ a wide range of frequencies as well as a wide range of spanwise modes. The calculated Reynolds number based on vorticity thickness is about $Re=2000$. Control authority is presented with PIV and hot-wire results. [Preview Abstract] |
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