Induced Velocity and Density Gradients due to Nanosecond Plasma Actuation

Abstract

An experimental and numerical investigation is presented on the effects due to the energy deposition induced by a nanosecond pulsed dielectric barrier discharge plasma actuator on a flat-plate boundary layer. High magnification rate particle image velocimetry was used in a phase-locked arrangement to resolve the velocity field after actuation. The parameters investigated were the orientation of the actuator with respect to the flow direction and the energy input. The backcurrent shunt technique was employed to monitor the high-voltage pulse and to calculate the energy input. Results indicate that effects induced by this type of plasma actuator are strongly dependent on the orientation of the actuator with respect to the direction of the flow. When the covered high-voltage electrode is in the upstream position, a region of decelerated flow is observed in the vicinity of the actuator. On the other hand, when the covered high-voltage electrode is in downstream position, a region of accelerated flow is observed, highlighting the presence of a weak directional body force in addition to the thermal energy deposition typically associated with nanosecond plasma actuation. The thermal energy deposition is responsible for considerable density gradients, which are calculated using the compressible continuity equation on the measured velocity fields. Calculations show good qualitative agreement with experimental schlieren imaging. In general, nanosecond pulsed dielectric barrier discharge plasma actuators appear to induce a combination of thermal effects manifested as density/viscosity gradients and momentum effects manifested as weak directional body forces.