Separation Control Using DBD Plasma Actuators: Designs for Thrust Enhancement S. Guo 1 , D. Burman 1 , D. Poon 1 , M. Mamunuru 1 , T. Simon 2 , D. Ernie 3 , and U. Kortshagen 4 University of Minnesota, Minneapolis, MN 55455 New plasma actuators designed for enhanced flow control authority are made by increasing asymmetry of thrust during the Dielectric Barrier Discharge (DBD) actuation cycle. This is done by a change of circuitry and by adding a semi-conductive layer on top of the dielectric surface, both for effective discharging of the dielectric. Compared to the conventional sinusoidal waveform driven plasma actuators, the new designs increases the thrust by about 70% when operating at the same frequency and voltage. Measurements indicate that increases in conductivity of the semi-conductive layer lead to increasingly higher thrust. I. Introduction ielectric Barrier Discharges (DBD) are plasmas far from equilibrium. 1 They are used in such applications as ozone synthesis, flat plasma displays, environmental protection, surface treatment, and layer deposition 2 . A single dielectric barrier plasma actuator for aerodynamic flow control 3 , consisting of a DBD operating in a surface- mode discharge with an asymmetric arrangement of electrodes, has the effect of imparting directed momentum to the flow in its vicinity. Corke et al. 4 demonstrated the potential of the plasma actuator for leading-edge separation control under high angle of attack applications. Their actuators were tested at an angle of attack of 16 o (4 o past the natural stall value of the airfoil) at Reynolds numbers of 70,000 and 158,000. The flow was found to be fully attached with the actuators on. Lift-to-drag ratio improvement of up to 400% and a clear reduction in drag forces were recorded. Smoke visualization indicated a much smaller wake than without actuation. D The effect of the plasma on a surrounding fluid is a result of collisional momentum transfer from the ions and electrons in the plasma with the neutral fluid molecules surrounding them. It is not a thermal effect. Increasing the trust generated by plasma actuators is important toward optimizing its performance for separation control. A computational study with air chemistry 5 indicates that the thrust generated in the backward discharge (when the exposed electrode is positive) is at least an order of magnitude higher than that produced during the forward discharge and that the forces are oppositely directed. It also predicts higher plasma density on the back discharge, creating an ion-dominated region responsible for the higher force. Experimental studies also indicate a difference between the forces generated during the two discharge half-cycles. One study 6 suggests that the forces are oriented in the same direction, but another study 7 , using FFT analyses of temporal measurements of actuator force acquired by an accelerometer, supports the conclusion of the computational study 5 that the forces are oppositely directed. A more recent study 8 , however, indicates that the asymmetry is even stronger than previously believed. They concluded that the stronger discharge accounts for most of the momentum coupling. In contrast to the previous result from the computation, though, the forward discharge (when the exposed electrode is negative) is considered to be the source of this dominant thrust. Another paper 9 is in qualitative agreement with this latter conclusion. It asserts that negative oxygen ions, especially , play the most important role in thrust production. − 2 O Despite the lack of clarity on the cause, nature, direction, and extent of the asymmetry in thrust generation, it is clear that asymmetry exists, offering some potential for improving the actuator performance by exploiting it. Although studies 5,7 showed different order of magnitude of the thrusts being generated during the backward American Institute of Aeronautics and Astronautics 1 1 Graduate Student, Department of Mechanical Engineering, Student Member AIAA. 2 Professor, Department of Mechanical Engineering. 3 Associate Professor, Department of Electronic and Computer Engineering. 4 Professor, Department of Mechanical Engineering. 39th AIAA Fluid Dynamics Conference 22 - 25 June 2009, San Antonio, Texas AIAA 2009-4184 Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.