Experimental damping of boundary-layer oscillations using DBD plasma actuators

In the present work artificially excited Tollmien–Schlichting waves were cancelled using plasma actuators operated both in continuous and pulsed modes. To achieve this a vibrating surface, driven by an electromagnetic turbulator, was flush-mounted in a flat plate to excite the TS waves. These were amplified by an adverse pressure gradient induced by an insert on the upper wall of the test section. Control plasma actuators positioned downstream of the excitation actuator attenuate the waves by imparting a steady or unsteady force into the boundary-layer. In the case with steady actuation the two actuators change the velocity profile of the laminar boundary-layer, which then attenuates the waves by itself. In the case of pulsed actuation the actuator creates an unsteady body force to counteract directly the oscillation. As a result the amplitude of the velocity fluctuations at the excitation frequency is reduced significantly in both cases. The principles and the results of the two sets of experiments are presented and discussed.