Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session G25: Flow Control IV: Plasma Actuators |
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Chair: Noel Clemens, University of Texas at Austin Room: 320 |
Monday, November 25, 2013 8:00AM - 8:13AM |
G25.00001: Real-time control of the boundary layer disturbance induced by a dynamic isolated roughness element using plasma actuators Kyle Bade, Ahmed Naguib, Ronald Hanson, Philippe Lavoie, Brandt Belson, Clarence Rowley It is well established that bypass boundary layer transition is initiated by the formation and growth of unsteady streaks. Motivated by the delay/prevention of transition, this study examines the ability to sense unsteady streaks in a Blasius boundary layer and to attenuate their transient growth. The unsteady streaks are introduced into the boundary layer using an isolated roughness element that is dynamically actuated from flush with the wall to a specified height; resulting in a time varying disturbance. A real-time, closed-loop, feedforward-feedback control system is designed to apply an appropriate voltage to a plasma actuator in order to reduce the roughness induced disturbance. The control system inputs come from two in-wall hot-wire shear stress sensors located within a high-speed streak disturbance, one upstream and one downstream of the plasma actuator. The controller is shown to effectively drive the shear stress at the feedback sensor toward the Blasius level. The flow state is later examined over a cross-flow plane above the feedback sensor to assess the effectiveness of the control in reducing the total disturbance energy. In addition, the effects of the control parameters on the controller's effectiveness and robustness are investigated. [Preview Abstract] |
Monday, November 25, 2013 8:13AM - 8:26AM |
G25.00002: Transition delay by introducing spanwise velocity gradients B.E.G. Fallenius, K. Barckmann, J.H.M. Fransson, S. Grundmann For stabilizing a boundary layer it has been shown both numerically and experimentally that the control idea of introducing steady spanwise velocity gradients\footnote{Cossu, C., Brandt, L. {\emph{Eur. J. Mech./B Fluids}} {\bf{23}}, 815, 2004.} is far more effective than what could be foreseen. Different devices have been analyzed experimentally, which can modulate the boundary layer in a controlled way, and so far miniature vortex generators\footnote{Shahinfar, S., Sattarzadeh, S. S., Fransson, J. H. M., Talamelli, A. {\emph{Phys. Rev. Lett.}} {\bf{109}}, 074501, 2012.} have shown to be the most coveted for transition delay. Currently, a popular control device in the control community is the plasma actuator, which mainly has shown its potential for separation control, but lately also for transition delay. In a wind tunnel investigation at KTH, the plasma actuators have been tested in a configuration aimed at making use of above control idea and its potential for transition delay will be discussed. [Preview Abstract] |
Monday, November 25, 2013 8:26AM - 8:39AM |
G25.00003: Effect of Pulsed Plasma Jets on Reflected Shock-Turbulent Boundary Layer Interaction Benton R. Greene, Noel T. Clemens, Patrick Magari, Daniel Micka Shock-induced turbulent boundary layer separation can have many detrimental effects in supersonic inlets including flow instability, fatigue of structural panels, poor pressure recovery, and unstart. Pulsed plasma jets (or ``spark jets''), zero net mass flow jets characterized by high bandwidth and the ability to direct momentum into the flow, are one promising method of reducing shock-induced separation and boundary layer distortion. The current study is focused on investigating the efficacy of pulsed plasma jets to reduce the boundary layer distortion induced by a reflected shock interaction in a Mach 3 flow. A 7$^{\circ}$ shock generator placed outside the tunnel ceiling boundary layer produces an incident shock on the floor of the tunnel of sufficient strength to induce separation. An array of pulsed plasma jets are placed approximately 2 boundary layer thicknesses upstream of the interaction and pulsed at between 1 kHz and 4 kHz. PIV is used to investigate the effect of the jets on the nature of the separation as well as the boundary layer distortion and pressure recovery downstream of the interaction. [Preview Abstract] |
Monday, November 25, 2013 8:39AM - 8:52AM |
G25.00004: The Influence of Spanwise Segmented Plasma Actuator Forcing on a Circular Cylinder Wake and the Selection of Optimum Wavelength Samik Bhattacharya, James W. Gregory Detailed investigations have been carried out on the effect of segmented plasma forcing on the wake of circular cylinder. Actuators of wavelength 1d to 6d (d$=$diameter) were used for three-dimensional actuation at Reynolds number of 4700. Two most important factors were wavelength of actuation and the power of plasma. Vortex shedding was not significantly attenuated below a certain threshold of the supplied voltage. However, for actuation wavelength more than 2d, the near wake developed a wavy profile due to emergence of streamwise vorticity. The reason for this development was differential displacement of the Karman vortex street behind the plasma forming and no plasma region. Forcing above the threshold voltage created strong circulating zones at each corner of the buried electrode, which diverted the flow from the no plasma region towards the plasma region. This process gave rise to alternate accelerated flow (behind the plasma region) and distinct reverse flow zones (behind no plasma regions). The strength of Karman shedding was attenuated as energy was extracted from it and fed to streamwise vorticity. This lead to significant reduction in drag in the event of high power actuation with 3d,4d and 5d actuators. The attenuation in shedding and reduction of drag was maximum for 4d actuator, which led to its selection as optimum wavelength. Significant difference in wake width was observed in high power forcing cases behind the two regions. This observation was attributed to spanwise difference in vortex formation length due to segmented forcing. [Preview Abstract] |
Monday, November 25, 2013 8:52AM - 9:05AM |
G25.00005: Experimental Study of the Power Profile Airfoil Equipped with Plasma Flow Control Libin Daniel, Jamey Jacob This presentation discusses results from an experimental study of the power profile airfoil at low Reynolds number. The power profile airfoil was developed by AMO Smith and consists of a blunt trailing edge shape with two wall jets near the trailing edge. The replacement of streamlining with properly designed blowing is used to prevent flow separation and additionally offers potential applications as a powered high-lift system, propulsive system, or low inertia control device. The 2D wind-tunnel model consists of the 22.5\% thick power profile airfoil equipped with a movable trailing edge plug to direct flow along the trailing edge streamline. Compressed air was passed into the model via a plenum with flow conditioning devices to create pressure backdrop to allow uniform blowing at the trailing edge. The effects of varying jet momentum coefficient and trailing edge positioning on the aerodynamic characteristics are observed with both wake surveys and PIV. The impact of plasma synthetic jet actuators (PSJA) placed along the trailing edge of the power profile airfoil is also discussed. PSJA operation is compared to the baseline power profile airfoil both alone and working with the blowing to provide additional control authority. [Preview Abstract] |
Monday, November 25, 2013 9:05AM - 9:18AM |
G25.00006: Vane Separation Control in a Linear Cascade with Area Expansion using AC DBD Plasma Actuators Christopher Kleven, Thomas Corke Experiments are presented on the use of AC dielectric barrier discharge (DBD) plasma actuators to prevent flow separation on vanes in a linear cascade with area expansion. The inlet Mach number to the cascade ranged from 0.3 to 0.5, and the vane chord Reynolds numbers ranged from $0.9\times10^6$ to $1.5\times10^6$. Three cascade designs with different amounts of area expansion, providing different degrees of adverse pressure gradients, were examined. Surface flow visualization revealed a 3-D separation bubble with strong recirculation that formed on the suction side of the vanes. The pattern agreed well with CFD simulations. Plasma actuators were placed on the suction sides of the vanes, just upstream of the flow separation location. Quantitative measurements were performed in the wakes of the vanes using a 5-hole Pitot probe. The measurements were used to determine the effect of the plasma actuator separation control on the pressure loss coefficient, and flow turning angle through the cascades. Overall, the plasma actuators separation control increased the velocity magnitude and dynamic pressure in the passage between the vanes, resulted in a more spanwise-uniform flow turning angle in the vane passage, and significantly lowered the loss coefficient compared to the baseline. [Preview Abstract] |
Monday, November 25, 2013 9:18AM - 9:31AM |
G25.00007: An Investigation of Plasma Actuators for Flow Control in a $140^{\circ}$ Bend Michael Arthur, Thomas Corke, Thomas Samper An experiment is presented to examine the effectiveness of AC dielectric barrier discharge (DBD) plasma actuators to maintain attached flow around a $140^{\circ}$ bend in a sector of a azimuthal channel. The Mach number at the inlet to the bend ranges from 0.10 to 0.23, and the static pressure ranges from 7 to 22 atmospheres. The plasma actuator is located just upstream of the natural flow separation location. It is designed to produce a net body force that is directed downstream and towards the wall. The requirements and design of the plasma actuator were augmented by a CFD simulation that included the plasma actuator body force vector field. The measurements consist of the static pressure distribution along the outside wall of the bend, and an array of total pressure sensors across the centerline of the exit of the bend. The pressure distribution across the channel showed the desired flattening of the mean pressure profile with increasing AC voltage and frequency that was indicative of a more uniform mass flow profile at the exit of the bend. These confirmed a plasma actuator effect that scaled linearly with the AC frequency, and with AC voltage to a power that is expected from the AC DBD analytical model. [Preview Abstract] |
Monday, November 25, 2013 9:31AM - 9:44AM |
G25.00008: DBD Control of a Turbulent Shear Layer downstream of a Backward Facing Step Patricia Sujar-Garrido, Nicolas Benard, Eric Moreau, Jean-Paul Bonnet The present paper deals with the control of a free shear layer downstream of a backward-facing-step of height 3 cm at Re 3x10$^{4}$. The initial boundary layer thickness is 1.2 cm with Re$_{\theta}$ 1200. The control is achieved via a single Dielectric Barrier Discharge (DBD). An optimal frequency is observed and it is shown that the plasma discharge is able to manipulate the first stages of the formation of the free shear layer and consequently to modify the flow dynamics of the entire flow; the results show some limitations of the control authority of this type of plasma discharge. Time unresolved and resolved measurements techniques are used to investigate the influence of plasma device on the global modification of mean reattachment length and on the large-scale structures and turbulent energy distribution. [Preview Abstract] |
Monday, November 25, 2013 9:44AM - 9:57AM |
G25.00009: Active Control of Natural Tollmien-Schlichting Waves using Plasma Actuators Marios Kotsonis, Ram Krishan Shukla, Stefan Probsting An experimental study is performed on active control of boundary layer instabilities developing on a NACA 0012 airfoil. A closed-loop control system has been implemented using the filtered-x Least Mean Squares adaptive algorithm based on Finite Impulse Response filters. Surface mounted microphones are used as sensors. The controller drives a Dielectric Barrier Discharge plasma actuator placed along the span of the airfoil. In contrast to the conventional sinusoidal signal, the actuator is powered using a continuously adapted signal selected by the controller in order to damp the incoming wavetrain of TS waves. High speed 2-component Particle Image Velocimetry is used to characterize the flow in the vicinity of the actuator. Several cases are tested using both open-loop and closed-loop actuation. Tested freestream velocities range from 17 to 25 $m/s$ at chord Reynolds of 0.22 to 0.33 million respectively. Results indicate the suppression of the tonal component of unstable TS waves with closed-loop actuation. Amplitude reduction of approximately 50 $\%$ is achieved for freestream velocity of 17 $m/s$ while significant suppression is maintained for higher velocities. In the case of open-loop control, the actuator is operated using non-adapted single-frequency sinusoidal signal. [Preview Abstract] |
Monday, November 25, 2013 9:57AM - 10:10AM |
G25.00010: Suppression or Enhancement of Pressure Fluctuations in High Subsonic Cavity Flow Using Plasma Actuators Mo Samimy, Kevin Yugulis, Samuel Hansford, James Gregory Localized arc filament plasma actuators (LAFPAs) were used to control pressure fluctuations in a Mach 0.6 cavity flow with a Reynolds number based on the cavity depth of 200,000. The rear wall of the cavity is inclined 30$^{\circ}$ with respect to the upstream flow and the cavity depth and length-to-depth ratio are 12.7 mm and 4.86. Five actuators were uniformly distributed along the span of the cavity 1 mm upstream of the cavity leading edge. Forcing was conducted quasi-two-dimensionally (all actuators operated in phase) and three-dimensionally (actuators operated out of phase). Time-resolved pressure and PIV measurements were used to assess the effectiveness of the actuators and to explore the physics of the flow. The results show that with proper selection of forcing frequency; (1) the cavity tone can be suppressed by over 20 dB and the broadband pressure fluctuations can be suppressed by over 5 dB in a strongly resonating cavity, and (2) the resonance can be re-established and the peak tone as well as the broadband pressure fluctuations can be significantly amplified in a weakly resonating cavity. Both quasi-two-dimensional and three-dimensional controls were successful in controlling the flow, but the control was less sensitive to forcing frequency change in the latter than former; and much wider forcing frequency range could be used in case (1) than case (2). [Preview Abstract] |
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