Flow Separation Control over a NACA 0015 Airfoil Using Nanosecond-Pulsed Plasma Actuator

The goal of the present study is to investigate the flow separation control process over a NACA 0015 airfoil model in a wind tunnel under the actuation of the nanosecond dielectric-barrier discharge plasma actuators at Reynolds numbers of 268,000 and 463,000. Detailed force measurements were carried out together with flowfield measurements employing time-resolved particle image velocimetry techniques. Both the force and particle image velocimetry measurements indicated that the nanosecond dielectric-barrier discharge functions as a trip device at the narrow range of angle of attack just around the stall angle, where a bistable mode exists for the original airfoil, which exhibits a leading-edge stall behavior. The particle image velocimetry measurements have shown that the few initial plasma discharges have much stronger effects on the separated flow compared to the subsequent plasma pulses, which is possibly due to the fact that the separated shear layer is altered and the separation location has shifted downstream, hence leading to the most receptive location moving away from the plasma actuation location. The separated flow undergoes a short period of transient flow state before reaching a quasi-periodic flow state. The transient flow state clearly exhibits a stronger tendency of flow attachment to the airfoil surface with less fluctuation compared to the subsequent quasi-periodic flow state. With the increase of the actuation frequency, the flow separation is further suppressed and delayed farther downstream under the conditions studied here.