Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session GD: Flow Control IV |
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Chair: Mo Samimy, Ohio State University Room: 101D |
Monday, November 23, 2009 8:00AM - 8:13AM |
GD.00001: Effect of Dielectric Properties on Functional Relationship between Plasma Initiation and Ambient Pressure Joseph Valerioti, Thomas Corke A parameter study is conducted using Single Dielectric Barrier Discharge (SDBD) plasma actuators. An experimental setup is used to determine the plasma initiation voltage for a range of pressure, frequency, dielectric thickness, and dielectric material. An actuator is placed in a sealed chamber evacuated to a given negative gage pressure. Peak-to-peak voltage of an AC sine wave is then increased until plasma formation is verified by means of light intensity. The variation of this initiation voltage is determined as a function of ambient pressure for different combinations of thickness/material of the SDBD dielectric. The relationship is then presented so as to assess its collapsibility to a parameter describing the ratio of the dielectric coefficient to the dielectric thickness, which is central to lumped element models used in plasma modeling. Future work will examine the relationship at pressures above atmospheric. [Preview Abstract] |
Monday, November 23, 2009 8:13AM - 8:26AM |
GD.00002: Effect of Actuation Parameters on Opposition Control of Transient Growth in a Blasius Boundary Layer Using Plasma Actuators Ronald Hanson, Philippe Lavoie, Ahmed Naguib This work is concerned with investigating an actuation scheme, using plasma actuators, designed to negate the effect of the transient growth instability occurring in a Blasius boundary layer and, by this means, delaying the bypass transition process. The actuators investigated consists of a spanwise array of symmetric plasma actuators, which are capable of generating spanwise periodic counter-rotating vortices. The effectiveness of the actuator array was tested on disturbances introduced via an array of cylindrical roughness elements. Early investigations have demonstrated a reduction of the total disturbance energy produced by the roughness elements by up to 68\% depending on the actuator geometry. In the present study, the focus is on determining the effect that the excitation signal supplied to the actuator, such as waveform, frequency and amplitude, can have on the receptivity of the boundary layer to the plasma forcing. It is found that the excitation can change the modal content of the disturbance introduced inside the boundary layer by the actuator. The consequences of these results are discussed with respect to actuator modelling and issues related to eventual integration with a feedback control system for transition control. [Preview Abstract] |
Monday, November 23, 2009 8:26AM - 8:39AM |
GD.00003: Preliminary numerical assessment of turbulent skin friction control with plasma actuators Bettina Frohnapfel, Antonio Criscione, Cameron Tropea, Yosuke Hasegawa, Nobuhide Kasagi Plasma actuators (PA) introduce a body force in the near-wall region of a fluid flow. This body force has already been successfully used for separation and transition flow control. We investigate the possibility of applying PAs to turbulent skin friction drag reduction by testing the effect of a modelled PA's body force in a numerically simulated turbulent channel flow. The body force is implemented into a control loop, which aims at impeding the spanwise velocity component near the wall surface. We assume to employ distributed sensors and actuators of finite size in order to investigate optimum actuator sizes for practical applications. Since the detailed physics of the body force generation by PAs and the resulting force distributions are still under study and a matter of discussion, we employ different models for the force distribution with the goal to identify the critical requirements for skin friction drag reduction with PAs. [Preview Abstract] |
Monday, November 23, 2009 8:39AM - 8:52AM |
GD.00004: S-Duct Engine Inlet Flow Control Using SDBD Plasma Streamwise Vortex Generators Christopher Kelley, Chuan He, Thomas Corke The results of a numerical simulation and experiment characterizing the performance of plasma streamwise vortex generators in controlling separation and secondary flow within a serpentine, diffusing duct are presented. A no flow control case is first run to check agreement of location of separation, development of secondary flow, and total pressure recovery between the experiment and numerical results. Upon validation, passive vane-type vortex generators and plasma streamwise vortex generators are implemented to increase total pressure recovery and reduce flow distortion at the aerodynamic interface plane: the exit of the S-duct. Total pressure recovery is found experimentally with a pitot probe rake assembly at the aerodynamic interface plane. Stagnation pressure distortion descriptors are also presented to show the performance increase with plasma streamwise vortex generators in comparison to the baseline no flow control case. These performance parameters show that streamwise plasma vortex generators are an effective alternative to vane-type vortex generators in total pressure recovery and total pressure distortion reduction in S-duct inlets. [Preview Abstract] |
Monday, November 23, 2009 8:52AM - 9:05AM |
GD.00005: Development of plasma streamwise vortex generators for increased boundary layer control authority Patrick Bowles, David Schatzman, Thomas Corke, Flint Thomas This experimental study focuses on active boundary layer flow control utilizing streamwise vorticity produced by a single dielectric barrier discharge plasma actuator. A novel plasma streamwise vortex generator (PSVG) layout is presented that mimics the passive flow control characteristics of the trapezoidal vane vortex generator. The PSVG consists of a common insulated electrode and multiple, exposed streamwise oriented electrodes used to produce counter-rotating vortical structures. Smoke and oil surface visualization of boundary layer flow over a flat plate compare the characteristics of passive control techniques and different PSVG designs. Passive and active control over a generic wall-mounted hump model, Re$_c$ = 288,000-575,000, are compared through static wall pressure measurements along the model's centerline. Different geometric effects of the PSVG electrode configuration were investigated. PSVG's with triangular exposed electrodes outperformed ordinary PSVG's under certain circumstances. The electrode arrangement produced flow control mechanisms and effectiveness similar to the passive trapezoidal vane vortex generators. [Preview Abstract] |
Monday, November 23, 2009 9:05AM - 9:18AM |
GD.00006: Plasma Enhanced Aerodynamics of Wind Turbine Blades John Cooney, Thomas Corke, Robert Nelson A series of computer simulations was conducted to determine the optimal method for reducing the chord length of large wind turbine blades while incorporating advanced flow control to offset the resulting loss in aerodynamic performance. The dominant building trend in the wind energy industry of turbines with progressively larger diameters provided the inspiration for this study. By reducing the chord along the inner region of the wind turbine blade, the total blade length could then be extended for the same mass of blade while limiting the additional costs and issues associated with increased blade length. In order to preserve certain geometric characteristics, the reduction in chord was achieved by scaling along the chord alone or by simply truncating the blade with a flat or circular cut. The aerodynamic requirements for the modified blade sections were to equal or better the total lift and the lift-to-drag ratio of the original blade sections. For this investigation, flow control consisted of plasma actuators located at a combination of the leading edge, maximum thickness, and trailing edge locations of the modified blade sections. [Preview Abstract] |
Monday, November 23, 2009 9:18AM - 9:31AM |
GD.00007: Noise reduction in a heated Mach 1.3 jet using plasma actuators Martin Kearney-Fischer, Mo Samimy Heating capabilities have recently been added to the free jet facility at the Gas Dynamics and Turbulence Laboratory (GDTL) of the Ohio State University using a storage-based off-line electric heater. This addition makes it possible to test the effectiveness of the localized arc filament plasma actuators (LAFPAs) for the purpose of either noise mitigation or mixing enhancement over a wide range of temperatures. These actuators have been used successfully at GDTL in high Reynolds number, high-speed unheated jets. The facility consists of an axisymmetric jet of exit diameter 2.54 cm with different nozzle blocks and variable jet temperature in an anechoic chamber. Previous work with a Mach 0.9 jet has shown significant increases in noise reduction effectiveness with increasing temperature. The next step is to determine if and how this trend continues in supersonic heated jets. A number of combinations of forcing azimuthal mode and temperature ratio at a wide range of forcing frequencies are experimented in a perfectly-expanded Mach 1.3 axisymmetric jet to examine LAFPAs effectiveness for far-field noise mitigation. The preliminary results to be presented indicate that the trends observed in the previous work continue in this supersonic jet. [Preview Abstract] |
Monday, November 23, 2009 9:31AM - 9:44AM |
GD.00008: Low dimensional analysis of the flow over a three dimensional turret Marlyn Andino, Mark Glauser The presence of turbulent flows in the path of a collimated beam produces degradation in its intensity hence abating its performance. A study of the flow physics around a cylindrical turret with the application of open-loop control has been performed. The evaluation of flow control performance is accomplished by analyzing the changes in the turbulent flow time/length scales across the turret surface for three cases. Even though these quantities are not direct measures of the aero-optics, literature suggest there is a strong relationship between them. Open-loop results demonstrate reductions in both RMS and Reynolds shear stress over the separated region. Results of the autocorrelations of the unsteady pressure sensors for the actuated low speed tests exhibit a more organized almost periodic behavior. We are interested in developing a low dimensional description of the flow field over a 3D turret through the use of velocity and unsteady surface pressure measurements. This will incorporate velocity/pressure correlations and mathematical tools such as Proper Orthogonal Decomposition and Modified Linear Stochastic Measurements to construct a low dimensional velocity-based closed-loop flow control model to estimate the flow states in real-time. [Preview Abstract] |
Monday, November 23, 2009 9:44AM - 9:57AM |
GD.00009: Active Flow Control over a 3D Articulating Turret Ryan D. Wallace, Patrick R. Shea, Vaithi Thirunavukkarasu, Henry Carlson, Mark N. Glauser An investigation of active flow control was conducted on an articulating 3D turret with a flat aperture using suction as the control input. Observability of the system was obtained by simultaneously sampled dynamic surface pressure at multiple locations around the aperture along with velocity flow field at the center plane of the turret. Both open loop and closed-loop control cases are examined for the purpose of reducing the turbulent fluctuations directly over the aperture. Open-loop control reduces the separation in the flow and decreases the levels of turbulence above the aperture. The large database of no control and open-loop control also provides a basis to develop closed-loop control. For closed-loop control, a simple proportional controller will feed back a low dimensional estimation of the flow based on dynamic surface pressure and velocity in an effort to improve upon the open-control cases. [Preview Abstract] |
Monday, November 23, 2009 9:57AM - 10:10AM |
GD.00010: Active Flow Control Techniques for use on Three Dimensional Hemispherical Turrets Patrick Shea, Ryan Wallace, Mark Glauser Hemispherical turrets have been a topic of considerable interest over the past several decades with studies focusing on airborne optical device applications. Highly three dimensional, turbulent flows develop in the wake of a turret, especially when a flat, optical aperture is in place on the hemisphere. Both open and closed-loop flow control have been successfully applied to this geometry to control the turbulent flow over the aperture, but control of large scale structures in the wake using open-loop flow control have been less effective. Fluctuating loads on the turret, which can induce undesired structural loading, have been attributed to strong, turbulent fluctuations in the velocity of the turret wake. The current work involves developing a more robust active control system (both open and closed-loop using suction based actuators) that will not only allow for the control of the flow over the aperture as Syracuse University is currently studying, but will also allow for control of the large scale flow structures that develop in the wake of a turret. [Preview Abstract] |
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