Ns-DBD plasma actuator induced density gradient on a laminar boundary layer

Abstract

An experimental investigation was conducted about the induced velocity and density gradients due to the effect of a nanosecond pulsed dielectric barrier discharge (ns-DBD) plasma actuator on a flat plate boundary layer. A particle image velocimetry (PIV), with a magnification about 1.26, was set-up in order to carry out this study. The tested plasma actuator was made out of a 2 layers Kapton tape barrier, with non-overlapping copper tape electrodes. It was mounted in a dedicated groove which allowed the tested actuator to be flush to the wall of a flat plate. Moreover, the flat plate was furnished with a super-elliptical leading edge so to produce a small positive pressure gradient meant to damp down instabilities due to surface aberrations and flow imperfections. Investigated parameters were the position of the covered electrode with respect to the flow direction and the energy input. Back-current shunt technique was applied in order to monitor the pulse discharged and to calculate the energy input. Results of discharge bursts of 50 pulses at 10kHz indicated that effects induced by a ns-DBD plasma actuator had a strong dependence on the stream wise location of the covered electrode with respect to the direction of the flow. When the covered high voltage electrode was in upstream position a region of about 0.5m/s decelerated flow was observed. On the contrary, when it was in downstream position a much thinner region about 0.5m/s accelerated flow was observed, highlighting the presence of a small directional body force. Moreover, density gradients were calculated resolving the compressible continuity equation implemented on a backward-time and backward-space finite difference discretization scheme. Results suggest that the area where density field is affected is larger for a covered electrode placed in upstream position. Moreover, a superposition of body force and density gradient could play a significant rule in optimization process of flow control strategies based on ns-DBD plasma actuators.