Active control of supersonic base flows with electric arc plasma actuators

The current paper evaluates the control authority of electric arc plasma actuators on a supersonic axisymmetric base flow for several actuator geometries, frequencies, forcing modes, duty cycles/on-times, and currents. The disturbances were tracked in time with phase-locked schlieren imaging and particle image velocimetry. The actuators caused moderate influences on the axisymmetric shear-layer velocity profile and base pressure. The most substantial changes to the shear layer and base pressure were noted for the highest current and duty cycle experiments. At 1A and 20% duty cycle, the base pressure was reduced by 3.5%. Similar changes were noted for all modes and a range of Strouhal numbers St_D from about 1.11 to 3.33 (10-30 kHz). Increases in duty cycle between 4 and 20% caused a nearly linear decrease in base pressure. Disturbances were tracked at all frequencies and translated along the shear layer at a convective velocity of 430 ± 20 m/s. A fairly clear trend of increasing velocity disturbance amplitude correlating to increasing base pressure changes was noted. Moreover, the ability of the disturbances to stay well organized farther down the shear layer also appears to be a significant factor in the actuators' effect on base pressure. Consistent with these observations, it appears that increased duty cycle causes increased shear-layer disturbance amplitudes.