Effects of nanosecond pulse driven plasma actuators on turbulent shear layers

The effects of nanosecond pulse driven dielectric barrier discharge plasma actuators on turbulent shear layers are examined experimentally on a mixing layer and backward facing step. The nanosecond pulse driven dielectric barrier discharge control mechanism is believed to be primarily thermal in contrast to most flow control actuators, including alternating current dielectric barrier discharges, which rely on periodic or pulsed momentum to excite shear-layer instabilities. Control authority using thermal perturbations has been demonstrated in various high-speed shear flows yet many questions on fundamental physics and scaling remain unanswered. This work aims to provide insight into both nanosecond pulse driven dielectric barrier discharges and thermal mechanisms in general for high-amplitude aerodynamic flow control. Previous studies suggest the efficacy of nanosecond pulse driven dielectric barrier discharges (and likely thermal perturbations in general) is strongly dependent on initial shear-layer conditions, namely some measure of the initial thickness. In an effort to support this hypothesis, boundary-layer suction is applied to a splitter plate upstream of a turbulent mixing-layer origin. This successfully reduces the initial mixing-layer momentum thickness, but does not result in substantial nanosecond pulse driven dielectric barrier discharge control authority. These results and the experimental conditions are documented in detail. Application of nanosecond pulse driven dielectric barrier discharge forcing to the turbulent shear layer downstream of a backward facing step having even smaller initial thickness produces the expected control authority for lower pulse amplitude than employed in the mixing-layer case. This supports the importance of initial shear-layer thickness (rather than state) for estimating potential control authority by nanosecond pulse driven dielectric barrier discharge and thermal perturbations in general.