Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session QJ: Flow Control VI |
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Chair: Mingjun Wei, New Mexico State University Room: Long Beach Convention Center 201A |
Tuesday, November 23, 2010 12:50PM - 1:03PM |
QJ.00001: Numerical and Experimental Investigation of Plasma Actuator Control of Modified Flat-back Airfoil Benjamin Mertz, Thomas Corke Flat-back airfoil designs have been proposed for use on the inboard portion of large wind turbine blades because of their good structural characteristics. These structural characteristics are achieved by adding material to the aft portion of the airfoil while maintaining the camber of the origional airfoil shape. The result is a flat vertical trailing edge which increases the drag and noise produced by these airfoils. In order to improve the aerodynamic efficiency of these airfoils, the use of single dielectric barrier discharge (SDBD) plasma actuators was investigated experimentally and numerically. To accomplish this, a rounded trailing edge was added to traditional flat-back airfoil and plasma actuators were used symmetrically to control the flow separation casued by the blunt trailing edge. The actuators were used asymmetrically in order to vector the wake and increase the lift produced by the airfoil similar to adding camber. [Preview Abstract] |
Tuesday, November 23, 2010 1:03PM - 1:16PM |
QJ.00002: Airfoil Leading Edge Flow Separation Control using DBD Plasma Actuators driven by Nanosecond Pulses Jesse Little, Chris Rethmel, Keisuke Takashima, Chris Wiet, Igor Adamovich, Mo Samimy This work continues an ongoing exploration of the use of dielectric barrier discharge plasma actuators driven by repetitive nanosecond pulses (NS-DBD hereafter) for aerodynamic flow control. The NS-DBD transfers very little momentum to the neutral air, but generates compression waves that manipulate flow instabilities similar to localized arc filament plasma actuators. Such devices which are believed to function through thermal effects and instability manipulation could result in a significant improvement over conventional DBD (AC-DBD) plasmas that rely on momentum addition which limits their performance at high speeds. The efficacy of NS-DBDs has been demonstrated in our laboratory in a preliminary work on an airfoil leading edge up to Mach 0.17 and Re=1x106. The current work extends the investigation to higher Mach (0.27) and Re (1.15x106), the maximum operating conditions of our subsonic wind tunnel, using an 8 inch chord NACA 0015 airfoil. Results show the efficacy of the nanosecond pulse plasma discharge for attaching the nominally separated flow at various post stall angles of attack. [Preview Abstract] |
Tuesday, November 23, 2010 1:16PM - 1:29PM |
QJ.00003: Experimental study and optimization of Plasma Actuators for Flow control in subsonic regime Pradeep Moise, Joseph Mathew, Kartik Venkatraman, Joy Thomas The induced jet produced by a dielectric barrier discharge (DBD) setup is capable of preventing flow separation on airfoils at high angles of attack. The effect of various parameters on the velocity of this induced jet was studied experimentally. The glow discharge was created at atmospheric conditions by using a high voltage RF power supply. Flow visualization, photographic studies of the plasma, and hot-wire measurements on the induced jet were performed. The parametric investigation of the characteristics of the plasma show that the width of the plasma in the uniform glow discharge regime was an indication of the velocity induced. It was observed that the spanwise and streamwise overlap of the two electrodes, dielectric thickness, voltage and frequency of the applied voltage are the major parameters that govern the velocity and the extent of plasma. The effect of the optimized configuration on the performance characteristics of an airfoil was studied experimentally. [Preview Abstract] |
Tuesday, November 23, 2010 1:29PM - 1:42PM |
QJ.00004: Pressure Dependence of Plasma Actuated Flow Control Joseph Valerioti, Thomas Corke An experimental investigation was conducted to determine how Single Dielectric-Barrier Discharge (SDBD) plasma actuators performed under variable ambient pressure. The static pressure was varied from 0.17 to 9.0 bar. The plasma initiation voltage and static thrust were measured and compared to similar data in literature. The results showed that at a given pressure, the plasma initiation voltage scaled with the actuator capacitor per unit area. The measured thrust showed the previously observed power-law relation with voltage, but the exponent varied with pressure. These trends were evaluated against simulations from the SDBD Space-Time Lumped Element Model. Parameters in the model affected by ambient pressure (capacitance, resistance, and Debye length of the air) were then systematically investigated to determine their effects on the plasma-produced body force. The overall trends were best modeled through a pressure dependence of the Debye length. [Preview Abstract] |
Tuesday, November 23, 2010 1:42PM - 1:55PM |
QJ.00005: Coherent Structures in a Supersonic Jet Excited by Plasma Actuators Datta Gaitonde, Mo Samimy Simulations are used in conjunction with experimental measurements to understand the coherent structures generated by excitation of a Mach 1.3 jet by eight localized arc filament plasma actuators uniformly distributed just upstream of the nozzle exit.~ Several modes are excited, including the axisymmetric (m=0), helical (m=1-3), and mixed modes (m=$\pm $1, $\pm $2) modes.~ The Strouhal number for all cases is fixed at 0.3, which corresponds to the most amplified frequency.~The simulations reproduce the distinct coherent structures measured in the experiment for each azimuthal mode.~ Detailed analysis of instantaneous, time- and phase-averaged quantities highlights a complex coherent structure generation, evolution and dissipation process. A key feature observed is the initiation of hairpin-like structures with tips/heads in the outer region of the jet shear layer and legs extending forward and slightly inclined in the direction of the jet axis, where the velocity is higher.~The subsequent interactions of these structures yield different composite structures in the downstream region. For example, for m=0, adjacent hairpin structures merge to yield axisymmetric rings, with the legs connecting successive structures in the form of ribs in the braid region; and with m=1 and 2 mode excitation, distinct helical and double-helical structures are observed, respectively, with the hairpins forming substructures in the coils. [Preview Abstract] |
Tuesday, November 23, 2010 1:55PM - 2:08PM |
QJ.00006: Towards Feedback Control of Bypass Transition: Experiments on Laminar Boundary Layer Response to Dynamically Actuated Roughness Kyle Bade, Ahmed Naguib, Ronald Hanson, Philippe Lavoie The current work details observations of the growth of streamwise streaks emanating from cylindrical roughness elements undergoing dynamic actuation into-and-out of a Blasius boundary layer flow. The growth and streamwise propagation of these motions is of interest in a larger study in collaboration with Princeton University in which a multi-university effort aims to develop and implement a robust feedback control system for the weakening/elimination of the streaks (because of their role in initiating bypass transition). Phase-averaged hotwire measurements in the transverse and spanwise directions provide two-dimensional visualizations of the spatial and temporal growth of these motions. Various roughness heights as well as actuation velocities are examined in order to identify the actuation parameters range for which the streaks can be produced while avoiding the introduction of T-S wave packets. This work validates the ability to introduce the proper disturbances into the boundary layer in preparation for the follow up control study. [Preview Abstract] |
Tuesday, November 23, 2010 2:08PM - 2:21PM |
QJ.00007: Towards Feedback Control of Bypass Transition: Experiments on Laminar Boundary Layer Response to a Pulsed Plasma Actuator Philippe Lavoie, Ronald Hanson, Ahmed Naguib Plasma actuators have recently been shown to negate the effect of the transient growth instability occurring in a Blasius boundary layer for the purpose of delaying bypass transition. Specifically, a spanwise array of symmetric plasma actuators generate a counter disturbance of spanwise periodic counter-rotating vortices. During steady operation, the total disturbance energy, introduced via an array of static cylindrical roughness elements, was reduced by up to 68\%, as shown by Hanson et al (Exp.\ Fluids, 2010). The objective of this work is to elucidate the dynamic response of a laminar boundary layer to pulsed excitation by the actuators used in the aforementioned study. The temporal evolution and decay of the disturbance is studied using phase-averaged hotwire measurements at a single plane located downstream of the actuator. The data provide insight into the spatio-temporal character of the modes excited by pulsed plasma actuation. Results are discussed with respect to eventual integration with a feedback control system in collaboration with Princeton University in a multi-university research program aimed at transition control. [Preview Abstract] |
Tuesday, November 23, 2010 2:21PM - 2:34PM |
QJ.00008: Towards Feedback Control of Bypass Transition: Numerical Simulations of Laminar Boundary Layer Response to a Plamsa Actuator Brandt Belson, Clarence Rowley We study the effects of single dielectric barrier discharge (SDBD) plasma actuators as a means to delay bypass transition in the Blasius boundary layer, with the eventual goal of closed-loop control. Since streamwise streaks are the structures with the largest transient growth, we orient an array of plasma actuators so as to produce spanwise forces and streamwise vorticity, and thus directly cancel the streaks. We use a pseudo-spectral solver to perform direct numerical simulations of the effect of plasma actuators, implemented as body forces. We compare two different models for the plasma actuator, and then apply each model to our spanwise geometry. We go on to compare each model's simulation results with experiments carried out by our collaborators at University of Toronto and Michigan State University as part of a multi-university research project. [Preview Abstract] |
Tuesday, November 23, 2010 2:34PM - 2:47PM |
QJ.00009: Improving Wind Turbine Efficiency with Plasma Actuators John Cooney, Thomas Corke, Robert Nelson As increasing the efficiency of modern wind turbines becomes more difficult, the use of active flow control now represents a more attractive means of possible improvement. This ongoing study examines utilizing single dielectric barrier discharge (SDBD) plasma actuators on wind turbine rotors to increase power generation. Blade element momentum (BEM) theory is used to identify regimes with the greatest potential for improvement and to estimate possible gains. Wind tunnel tests are conducted with plasma actuators to determine the amount of aerodynamic control achievable. In addition, the scope of a new ``Laboratory for Enhanced Wind Energy Design'' is outlined. Most critically, this resource includes two full-scale wind turbines to balance the known limitations of existing theory and wind tunnel testing by providing the capability to test novel blade designs and control strategies in the field. [Preview Abstract] |
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