Experiments and simulation of plasma actuators with enhanced thrust U. Kortshagen 1 , S. Guo 1 , M. Mamunuru 1 , D. Ernie 2 , and T. W. Simon 1 1 Dept. of Mechanical Engineering, University of Minnesota, Minneapolis, MN-55455, USA 2 Dept. of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN-55455, USA Abstract: Dielectric barrier discharge (DBD) plasma actuators can be used in flow con- trol applications due to the momentum transfer from the plasma species to the fluid. To date, the relatively small thrust obtained with DBD plasma actuators has been a major impediment. Here, different plasma actuator configurations for enhancing the thrust are introduced. Experiments demonstrate that some of the new configurations increase the thrust compared to the standard actuator. Simulations are performed to explain the thrust generation. Keywords: DBD plasma actuator; thrust; amorphous silicon; streamer; plasma simula- tion. Introduction One of the most promising prospective applications of the asymmetric DBD plasma actuators is the flow separation control over an air foil [1-5]. A single dielec- tric barrier aerodynamic plasma actuator [3] consisting of a DBD operating in a surface discharge mode with an asymmetric arrangement of electrodes has the effect of imparting directed momentum to the flow in its vicinity. The body force (thrust) generated by the DBD plasma actuator during this momentum transfer may play an important role in separation control. Thus, enhancement of the thrust is an important objective which is now be- ing studied by many groups [3, 6-15]. Both computational [5] and experimental studies [6] indicate a difference between the forces generated during the two half-cycles in a sinusoidal waveform driven dis- charge. They suggest that the forces are oppositely di- rected and lead to a partial thrust cancellation resulting in a reduced net thrust. The surface charge deposited on the dielectric during one half-cycle is believed to be an im- portant factor in the thrust cancellation. Hence there is significant interest in enhancing the asymmetry between the two discharge half cycles and reducing the impact of the surface charge. This paper focuses on new schemes to enhance the discharge asymmetry to obtain enhanced thrust for a plasma actuator. Our computational work aims at understanding the physics of the actuator dis- charge and the cause of net thrust. Experimental setup and results A traditional plasma actuator usually consists of an uncovered, powered electrode and a buried grounded electrode, both separated by a dielectric. In this study, a third electrode and a conducting material layer are added to the traditional plasma actuator to enhance the level of the asymmetry, as shown in Fig 1. The addi- tional electrode is connected through high voltage di- odes to the voltage source; it is intended to actively draw parts of the surface charge from the dielectric sur- face so that the thrust cancellation during different half-cycles can be minimized. As shown in Fig 1 (b), when the upper left electrode is negative, the diodes are in reverse direction so that the third electrode remains floating; the discharge will break down only between the left electrode and the dielectric surface. When the upper left electrode is positive with respect to the third electrode, the diodes are in forward direction, so that the discharge can occur between the dielectric surface and both the upper electrodes, which will cause some of the surface charge to be drained to the third electrode. The induced asymmetry may help reduce the thrust cancellation between forward and reverse pulse. Additionally, an amorphous (hydrogenated) silicon (a-Si) thin film is introduced as the conductive layer in the plasma actuator. Naude et al. [16] have found that the conductivity of the surface will clearly influence the formation of micro-discharges in the DBD. We hy- pothesize that this layer enhances the surface charge dissipation compared to a dielectric material, thus it may help to drain the surface charge more effectively. (a) (b) Fig 1: New plasma actuator design: (a) scheme of the new design; (b) the third electrode can actively dissipate part of the surface charge from the dielectric surface.