Large eddy simulation of dynamic stall flow control for wind turbine airfoil using plasma actuator

Abstract

To solve aerodynamic performance deterioration caused by dynamic stall, a large eddy simulation numerical calculation based on dynamic grid and sliding grid technology was conducted and the dynamic flow control mechanism of unsteady pulsed plasma was explored. The results showed that plasma aerodynamic actuators can effectively control the airfoil’s dynamic stall, improve the mean and transient aerodynamic forces, and reduce the negative peak value of the pitch moment and hysteresis loop area. A negative pressure “bulge” appears in the plasma application areas, and the peak suction of the airfoil’s upper surface obviously increases. Two unsteady control parameters, the pulsed frequency and duty cycle, significantly influence the flow control. When the dimensionless pulsed frequency is 1.5, plasma control improves, and when the duty cycle is 0.8, it is close to the aerodynamic benefits under the continuous working mode. In the deep stall state, plasma impels the flow separation position to obviously move backward, resisting large-scale dynamic stall vortices. The structure of the separation vortices is broken, dissipated, and reattached to the airfoil by the plasma, and the influence area of the vortices is reduced. In the light stall state, the plasma actuator easily controls the shear layer, inducing the transition of the airfoil’s boundary layer and promoting the momentum mixing with the main flow. “Vortex clusters” near the airfoil’s leading edge induced by plasma actuation play a role in the virtual aerodynamic shape. The harmonic oscillation of aerodynamic force/moment is caused by the nonlinear and strong coupling effect between dynamic vortex structures with different scales and frequencies and plasma aerodynamic actuation. The amplitude of low-order mode energy concentration is relatively large, which is mainly caused by the pitching motion. The high-order fluctuation energy concentration is caused by the evolution process of starting vortices and derived secondary vortices with different frequencies induced by plasma.