Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session M7: Flow Control: Plasma, Actuators and Synthetic Jets |
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Chair: Michael Amitay, Rensselaer Polytechnic Institute Room: B115 |
Tuesday, November 22, 2016 8:00AM - 8:13AM |
M7.00001: More Insight of Piezoelectric-based Synthetic Jet Actuators Kevin Housley, Michael Amitay Increased understanding of the internal flow of piezoelectric-based synthetic jet actuators is needed for the development of specialized actuator cavity geometries to increase jet momentum coefficients and tailor acoustic resonant frequencies. Synthetic jet actuators can benefit from tuning of the structural resonant frequency of the piezoelectric diaphragm(s) and the acoustic resonant frequency of the actuator cavity such that they experience constructive coupling. The resulting coupled behavior produces increased jet velocities. The ability to design synthetic jet actuators to operate with this behavior at select driving frequencies allows for them to be better used in flow control applications, which sometimes require specific jet frequencies in order to utilize the natural instabilities of a given flow field. A parametric study of varying actuator diameters was conducted to this end. Phase-locked data were collected on the jet velocity, the cavity pressure at various locations, and the three-dimensional deformation of the surface of the diaphragm. These results were compared to previous analytical work on the interaction between the structural resonance of the diaphragm and the acoustic resonance of the cavity. [Preview Abstract] |
Tuesday, November 22, 2016 8:13AM - 8:26AM |
M7.00002: Vectoring of parallel synthetic jets: A parametric study Tim Berk, Guillaume Gomit, Bharathram Ganapathisubramani The vectoring of a pair of parallel synthetic jets can be described using five dimensionless parameters: the aspect ratio of the slots, the Strouhal number, the Reynolds number, the phase difference between the jets and the spacing between the slots. In the present study, the influence of the latter four on the vectoring behaviour of the jets is examined experimentally using particle image velocimetry. Time-averaged velocity maps are used to study the variations in vectoring behaviour for a parametric sweep of each of the four parameters independently. A topological map is constructed for the full four-dimensional parameter space. The vectoring behaviour is described both qualitatively and quantitatively. A vectoring mechanism is proposed, based on measured vortex positions.\\ \\ We acknowledge the financial support from the European Research Council (ERC grant agreement no. 277472). [Preview Abstract] |
Tuesday, November 22, 2016 8:26AM - 8:39AM |
M7.00003: Experimental and Computational Investigation of a Dual-Throat Thrust Vectoring Nozzle John Farnsworth, Naveen Penmetsa, Ryan Starkey The dual-throat fluidic thrust vectoring nozzle is of particular interest because of its ability to provide large vector angles with minimal losses in thrust. This work investigated the performance of a dual-throat fluidic thrust vectoring nozzle for three secondary injection geometries: two spanwise oriented rectangular slots of two thicknesses, and a single spanwise oriented array of circular holes. Initial testing of the nozzles at a nozzle pressure ratio of two showed that the presence of the injection geometry alone influenced the baseline vector angle of the flow. With the introduction of secondary injection, the thinner rectangular slot was found to outperform the two other configurations at low injection percentages, while secondary injection through an array of holes trended higher at higher injection percentages. Using the experimental and computational data collected during this study, a method was developed to predict vector angle from the wall static-pressure distributions internal to the nozzle. The predicted thrust-vector angle matched the angles measured from schlieren photographs to within the measurement uncertainty across the range of injection mass flow rates tested. [Preview Abstract] |
Tuesday, November 22, 2016 8:39AM - 8:52AM |
M7.00004: Towards In-Flight Applications? - Requirements on the Dielectric Barrier Discharge (DBD) Plasma Actuator (PA) Jochen Kriegseis, Bernhard Simon, Sven Grundmann Most of today’s flow control (FC) efforts with DBD show a rather one-sided picture. Typically, either the discharge properties are discussed extensively or FC achievements are reported. The former group of contributions only pays limited attention to implications and consequences of most characteristics with respect to subsequent control steps for successful DBD-based FC - the latter group mostly ignores changing discharge properties, thus varying control authority for the respective applications when changes of environment, PA health state or simply a varied angle-of-attack are to be considered. In addition, there still remains a fair bit of uncertainty regarding a universal PA-evaluation metric, such that some of the most promising quantities/characteristics for successful controller operation remain largely untouched from the community. The purpose of the present work is to outline the requirement profile of PAs in one coherent story starting from electrical issues all the way down the road to in-flight FC success, where particular emphasis is placed on the interplay of the involved subtopics. It is hypothesized that such a clear guideline is the only way to advance beyond the present level of lab studies, where there still is an obvious lack of real flight applications. [Preview Abstract] |
Tuesday, November 22, 2016 8:52AM - 9:05AM |
M7.00005: Study of shock shape and strength as a function of plasma energy using background oriented schlieren and shadowgraph. Bhavini Singh, Lalit Rajendran, Matthew Giarra, Sally Bane, Pavlos Vlachos The formation of a spark is a random, chaotic process. The flow field generated by this spark can be used in flow control and plasma assisted combustion applications. In order to understand the flow field some time after spark discharge (approximately 1 microsecond), it is important to observe the shape and strength of the shockwave immediately following the plasma discharge. It is also important to understand the effect that the energy deposited in the spark gap has on the shock strength and shock shape. We therefore propose a background oriented schlieren (BOS) technique to measure density gradients associated with the spark discharge and hence quantify shock strength. Simultaneous shadowgraph measurements will be used to observe the shape of the shock and compare it with the reconstructed density gradients obtained from BOS measurements. [Preview Abstract] |
Tuesday, November 22, 2016 9:05AM - 9:18AM |
M7.00006: Pulsed-DC DBD Plasma Actuators Alan Duong, Ryan McGowan, Katherine Disser, Thomas Corke, Eric Matlis A new powering system for dielectric barrier discharge (DBD) plasma actuators that utilizes a pulsed-DC waveform is presented. The plasma actuator arrangement is identical to most typical AC-DBD designs with staggered electrodes that are separated by a dielectric insulator. However instead of an AC voltage input to drive the actuator, the pulsed-DC utilizes a DC voltage source. The DC source is supplied to both electrodes, and remains constant in time for the exposed electrode. The DC source for the covered electrode is periodically grounded for very short instants and then allowed to rise to the source DC level. This process results in a plasma actuator body force that is significantly larger than that with an AC-DBD at the same voltages. The important characteristics used in optimizing the pulsed-DC plasma actuators are presented. Time-resolved velocity measurements near the actuator are further used to understand the underlying physics of its operation compared to the AC-DBD. [Preview Abstract] |
Tuesday, November 22, 2016 9:18AM - 9:31AM |
M7.00007: Turbulent Mixing Layer Control using Ns-DBD Plasma Actuators Ashish Singh, Jesse Little A low speed turbulent mixing layer ($Re_{\theta_o}$=1282, $U_1/U_2=0.28$ and $U_2=11.8m/s$) is subject to nanosecond pulse driven dielectric barrier discharge (ns-DBD) plasma actuation. The forcing frequency corresponds to a Strouhal number ($St$) of 0.032 which is the most amplified frequency based on stability theory. Flow response is studied as a function of the pulse energy, the energy input time scale (carrier frequency) and the duration of actuation (duty cycle). It is found that successful actuation requires a combination of forcing parameters. An evaluation of the forcing efficacy is achieved by examining different flow quantities such as momentum thickness, vorticity and velocity fluctuations. In accordance with past work, a dependence is found between the initial shear layer thickness and the energy coupled to the flow. More complex relationships are also revealed such as a limitation on the maximum pulse energy which yields control. Also, the pulse energy and the carrier frequency (inverse of period between successive pulses) are interdependent whereby an optimum exists between them and extreme values of either parameter is inconsonant with the control desired. These observations establish a rich and complex process behind ns-DBD plasma actuation. [Preview Abstract] |
Tuesday, November 22, 2016 9:31AM - 9:44AM |
M7.00008: Transitory Control of the Aerodynamic Loads on an Airfoil in Dynamic Pitch and Plunge Yuehan Tan, Thomas Crittenden, Ari Glezer Transitory control and regulation of trapped vorticity concentrations are exploited in wind tunnel experiments for control of the aerodynamic loads on an airfoil moving in time-periodic 2-DOF (pitch and plunge) beyond the dynamic stall margin. Actuation is effected using a spanwise array of integrated miniature chemical (combustion based) high-impulse actuators that are triggered intermittently relative to the airfoil's motion. Each actuation pulse has sufficient control authority to alter the global aerodynamic performance throughout the motion cycle on a characteristic time scale that is an order of magnitude shorter than the airfoil's convective time scale. The effects of the actuation on the aerodynamic characteristics of the airfoil are assessed using time-dependent measurements of the lift force and pitching moment coupled with time-resolved particle image velocimetry that is acquired phased-locked to the motion of the airfoil. It is shown that the aerodynamic loads can be significantly altered using actuation programs based on multiple actuation pulses during the time-periodic pitch/plunge cycle. Superposition of such actuation programs leads to enhancement of cycle lift and pitch stability, and reduced cycle hysteresis and peak pitching moment. [Preview Abstract] |
Tuesday, November 22, 2016 9:44AM - 9:57AM |
M7.00009: Closed-Loop Flow Control of the Coupled Wake Dynamics and Aerodynamic Loads of a Freely-Pivoting 3-DOF Bluff Body T. Lambert, B. Vukasinovic, A. Glezer The motion of an axisymmetric bluff body model that is free to pivot in pitch, yaw, and roll in a uniform stream in response to flow-induced aerodynamic loads is controlled in wind tunnel experiments using fluidic actuation. The model is attached to an upstream, wire-supported short streamwise sting through a low-friction hinge, and each of the support wires is individually-controlled by a servo actuator through an in-line load cell. The aerodynamic loads on the body, and thereby its motion, are controlled through fluidic modification of its aerodynamic coupling to its near wake using four independent aft mounted synthetic jet actuators that effect azimuthally-segmented flow attachment over the model's tail end. The effects of actuation-induced, transitory changes in the model's aerodynamic loads are measured by its motion response using motion tracking, while the coupled evolution of the near-wake is captured by high-speed stereo PIV. Flow control authority is demonstrated by feedback-controlled manipulation of the model's dynamic response, and dynamic mode decomposition (DMD) of the wake is used to characterize changes in the wake structure and stability. It is shown that this flow control approach can modify the stability and damping of the model's motion (e.g., suppression or amplification of its natural oscillations), and impose desired directional attitude. [Preview Abstract] |
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