Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session G09: Flow Control: Plasma Actuators (5:00pm  5:45pm CST)Interactive On Demand

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G09.00001: Higher Order Response of the Laminar Boundary Layer to a Step Input by Spanwise Periodic Forcing Hossein Khanjari, Ronald Hanson The Blasius boundary layer response to a step input forcing by a streamwise array of simulated plasma actuators is studied. The actuators' effect is simulated in a commercial computational fluid dynamics code. A parametric study is used to calibrate an applied momentum source that simulates the actuators' output. Both the spatial distribution and the magnitude of the momentum source are tuned to match an experimental dataset that is limited to measurements of the streamwise velocity. For the step response, the simulated actuators are activated for approximately 80 boundary layer turnover times and then switched off. This choice of actuation parameter is sufficient to reach an approximately steady state at the downstream planes considered prior to deactivation of the actuators. In the far field region downstream of the actuators, the response to forcing exhibits a higher order response with respect to the shear stress, which is attributed to secondary vortex structures produced by the actuators as the primary vortices are convected downstream. The magnitude of the resulting streamwise velocity streaks caused by the actuators also exhibits a higher order response. The observed overshoots are shown to be caused by the rearrangement of the boundary layer during the onset of forcing. [Preview Abstract] 

G09.00002: Estimation of vorticity generated due to shock curvature in spark induced flow. Bhavini Singh, Lalit Rajendran, Pavlos Vlachos, Sally Bane Spark plasma discharges induce a complex, transient flow field. The spark discharge induces a shock wave at early times, that propagates radially outward from the electrode gap. The discharge also creates a hot gas kernel, and a pair of vortex rings in the electrode gap. It has been shown that long after the shock wave has departed the field of view, a vortexdriven mixing flow is produced, where the pair of vortex rings drive cooling of the hot gas kernel. The spark induced vorticity therefore plays a key role in the heat transfer and dynamics of the induced flow field. The mechanism(s) responsible for the generation of this vorticity and the effect of electrical energy deposited in the gap on the vorticity remain unresolved. In this work, we develop a detailed, analytical framework to estimate the vorticity generated due to the curvature of the induced shock wave and compare this to the magnitude of vorticity in the vortex rings for a range of energy values. We perform 700 kHz schlieren measurements to capture the induced shock wave and 50 kHz time resolved, stereoscopic, particle image velocimetry measurements of the velocity field to calculate the induced vorticity. This is a first step in understanding the role of the shock wave in vorticity generation and provided a framework for further research in the area. [Preview Abstract] 

G09.00003: Turbulent convective heat transfer control with plasma actuators Rodrigo Castellanos, Theodoros Michelis, Stefano Discetti, Andrea Ianiro, Marios Kotsonis The use of DBD plasma actuators as a technique for active heat transfer control in turbulent flows is experimentally investigated in this work. A streamwiseoriented Dielectric Barrier Discharge plasma actuator array introduces a controlled disturbance upstream of the heat flux sensor. The actuator layout aims at generating opposing plasma plumes, causing a liftup of flow in the direction normal to the wall, which eventually leads to the formation of counterrotating streamwise vortices. The flow is investigated with both planar and stereoPIV in multiple parallel planes, enabling reconstruction of the threedimensional mean flow field. IR thermography reveals plasmainduced formation of streamwise streaks on the wall surface where convective heat transfer is reduced. Each streak coincides with the spanwise position where the plasma jets lift off. The opposing plasma discharge liftsup the boundary layer, leading to a lowvelocity region that grows in the streamwise direction. In the lower region of the boundary layer, the flow induced by the actuation blocks the main flow, leading to localized lowvelocity regions above the exposed electrodes. This phenomenon is a consequence of the actuator suction, extracting fluid from its surroundings [Preview Abstract] 

G09.00004: Optimization of DielectricBarrierDischarge Vortex Generators by numerical simulation Patricia Sujar Garrido, Marley Becerra, P. Henrik Alfredsson, Ramis \"Orl\"u A DielectricBarrierDischarge (DBD) actuator has various design parameters related to its geometry, electrical settings, and the materials used which affect its efficiency. In the particular case of DBD Vortex Generators the parameter space is increased by the wavelength, the direction of the flow angle, and the orientation for a formation of co or counterrotating vortices. For its optimization for practical applications, all these parameters can be hardly manipulated isolating their dependencies in experimental investigations. A costefficient way to manage this optimisation process is by numerical simulations. The most used numerical model (SuzengHuang Model) simulates the DBD's effects, but it needs as input parameters physical quantities that cannot be directly measured. They are instead tuned to agree with a given set of experimental data. Hence, velocity and electric measurements of a single DBD are used for calibrating the SH model. The assessment of this model in the context of an optimization study for DBD VGs, incorporating the electrical point of view, by combining experimental and numerical studies, is currently on the way. [Preview Abstract] 

G09.00005: Experimental Assessment of How Distance Between Two Plasma Actuator Affect a Quiescent Flow Andrew Quinton, Alvin Ngo, Jamey Jacob In the past, Cold atmospheric pl\textbf{asma (CAP) has been used }in the aerospace industry, for active flow control\textbf{.} In this experiment,\textbf{ the effects of flow control are expanded on by measuring how the distance between} \textbf{two surface dielectric barrier discharge (SDBD) actuators affect a }quiescent\textbf{ flow. The two SDBD actuators will be placed on a flat surface at a far enough distance to be outside the influence of each other and slowly pushed in. The goal of this study is to find a distance where the flow from the first SDBD actuator flows smoothly into the second SDBD actuator to generate the optimal induced velocity. The velocity vectors will be obtained using a }particle image velocimetry\textbf{ (PIV) setup. The expected results are that} the \textbf{second SDBD actuator will interrupt the flow from the first actuator when it is too close by producing a counter ionic wind, and will have little to no effect on each other when they are far enough apart.} [Preview Abstract] 
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