Influence of Actuating Position on Asymmetric Vortex Control With Nanosecond Pulse DBD Plasma Actuators

Abstract

An experimental study of flow control over conical body by nanosecond pulse dielectric barrier discharge (NS-DBD) plasma actuation at Re $_{D} = 3.09 \times 10^{5}$ ( ${v} = 42$ m/s) is presented. First, the fundamental characteristics and control mechanisms of the plasma actuator were studied in the quiescent atmosphere. NS-DBD plasma actuator is an economical effective device because of its high discharge voltage/frequency ( $\sim 20$ kV/20 kHz), but short pulse duration time ( $\sim 20$ ns). Plasma actuators with different geometries were studied using the Schlieren technique. On the microsecond time scale, combination compression waves that consisted of a hemisphere wave and a planar wave were generated by rapid gas heating. The propagation velocity produced during the initial stage (10–40 $\mu \text{s}$ ) can potentially reach the sonic level ( $\sim 350$ m/s). On the millisecond time scale, two starting vortices rolled up from two opposite directions, and then developed into one perturbation downstream. NS-DBD plasma actuation influences the flow by rapid localized heating and transferring energy to the near-wall gas. In the wind tunnel experiment, a pair of NS-DBD plasma actuators mounted symmetrically on the surface of the model apex were applied to control the asymmetric vortex flow field. Actuators were, respectively, aligned along the line of azimuth angles of $\theta = \pm 80^{\circ }$ , ±90°, and ±100°, under positive and negative discharges. The test results include the pressure distribution sampled over the measurement station and the calculated lateral force coefficient. The efficacy of NS-DBD plasma actuation for controlling the asymmetric vortex over conical body was demonstrated with arrangements $\theta = \pm 80^{\circ }$ and $\theta = \pm 90^{\circ }$ . The results suggest that the actuator should be set before the suction peak point. When the flow started to accelerate and separate, the small perturbation created by NS-DBD could hardly control the flow. Pressure distributions under plasma actuation with different discharge directions indicate that the control power of NS-DBD is directional and is located along the discharge direction. The actuation with positive discharge delays the separation, whereas the actuation with negative discharge fixed separates the flow.