Dielectric Barrier Discharge Flow Control at Very Low Flight Reynolds Numbers

Abstract

Experiments were performed on a flat-plate airfoil and an Eppler E338 airfoil at very low flight Reynolds numbers (3000 ≤ Re ≤ 50,000), in which dielectric barrier discharge plasma actuators were employed at the airfoil leading edges to effect flow control. The actuators were driven in a high-frequency (kilohertz) steady mode and a pulsed mode in which pulse frequency and duty cycle were varied in a systematic fashion. Optimum reduced frequencies for generating poststall lift were approximately between 0.4 and 1, and this was broadly consistent with zero-mass-flux slot-blowing data acquired at Reynolds numbers that were approximately 200 times higher. Nevertheless, profound differences in the response to reduced frequency and duty cycle were observed between the flat-plate and E338 airfoils. In general, actuation produced considerable performance improvements, including an increase in maximum lift coefficient of 0.4 to 0.8 and maintained elevated endurance at significantly higher lift coefficients. Actuation in the steady mode resulted in circulation control at Re = 3000. Pulsed actuation also exerted a significant effect on the wake at prestall angles of attack, in which control of the upper-surface flat-plate bubble shedding produced significant differences in wake spreading and vortex shedding. The flat plate was also tested in a semispan-wing configuration (AR = 6), and the effect of control was comparable with that observed on the airfoil.