Experimental investigation of dynamic stall flow control using a microsecond-pulsed plasma actuator

To alleviate the performance deterioration caused by dynamic stall of a wind turbine airfoil, the flow control by a microsecond-pulsed dielectric barrier discharge (MP-DBD) actuator on the dynamic stall of a periodically pitching NACA0012 airfoil was investigated experimentally. Unsteady pressure measurements with high temporal accuracy were employed in this study, and the unsteady characteristics of the boundary layer were investigated by wavelet packet analysis and the moving root mean square method based on the acquired pressure. The experimental Mach number was 0.2, and the chord-based Reynolds number was 870 000. The dimensionless actuation frequencies F (+) were chosen to be 0.5, 1, 2, and 3, respectively. For the light dynamic regime, the MP-DBD plasma actuator plays the role of suppressing flow separation from the trial edge and accelerating the flow reattachment due to the high-momentum freestream flow being entrained into the boundary layer. Meanwhile, actuation effects were promoted with the increasing dimensionless actuation frequency F (+). The control effects of the deep dynamic stall were to delay the onset and reduce the strength of the dynamic stall vortex due to the accumulating vorticity near the leading edge being removed by the induced coherent vortex structures. The laminar fluctuation and Kelvin-Helmholtz (K-H) instabilities of transition and relaminarization were also mitigated by the MP-DBD actuation, and the alleviated K-H rolls led to the delay of the transition onset and earlier laminar reattachment, which improved the hysteresis effect of the dynamic stall. For the controlled cases of F (+) = 2, and F (+) = 3, the laminar fluctuation was replaced by relatively low frequency band disturbances corresponding to the harmonic responses of the MP-DBD actuation frequency.