Separation Control with Nanosecond-Pulse-Driven Dielectric Barrier Discharge Plasma Actuators

Abstract

The efficacy of dielectric barrier discharge (DBD) plasmas driven by high voltage (~15 kV) repetitive nanosecond pulses (~100 ns FWHM) for flow separation control is investigated experimentally on an airfoil leading edge up to Re=1x106 (62 m/s). Unlike AC-DBDs, the nanosecond pulse driven DBD plasma actuator transfers very little momentum to the neutral air, but generates compression waves similar to localized arc filament plasma actuators. A complex pattern of quasi-planar and spherical compression waves is observed in still air. Measurements suggest that some of these compression waves are generated by discharge filaments that remain fairly reproducible pulse-to-pulse. The device performs as an active trip at high Re pre-stall angles of attack and provides perturbations that generate coherent spanwise vortices at post-stall. These coherent structures entrain freestream momentum thereby reattaching the normally separated flow to the suction surface of the airfoil. Coherent structures are identified at all tested frequencies, but values of Fc+=4-6 are most effective for control. Such devices which are believed to function through thermal effects could be an alternative to AC-DBD plasmas that rely on momentum addition.