NUMERICAL STUDY ON DYNAMIC STALL FLOW CONTROL FOR WIND TURBINE AIRFOIL USING PLASMA ACTUATOR 1)

In order to solve the problem of aerodynamic performance deterioration caused by dynamic stall, based on the dynamic grid and sliding grid technology, the large eddy simulation numerical calculation is carried out, and the dynamic flow control mechanism of unsteady pulsed plasma is explored. The results show that the plasma aerodynamic actuator can effectively control the airfoil dynamic stall, improve the mean and transient aerodynamic forces, and reduce the negative peak value of the pitch moment and the area of the hysteresis loop. The negative pressure "bulge" appears in the plasma application areas, and the peak suction of the upper airfoil surface increases obviously. The two unsteady control parameters, pulsed frequency and duty cycle, have significant influence on the flow control. When the dimensionless pulsed frequency is 1.5, the plasma control effect is better, 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: the plasma impels the flow separation position to move backward obviously, which resists the occurrence of 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 has strong ability to control the shear layer, which induces the transition of the airfoil boundary layer in advance and promotes the momentum mixing with the main flow. The "vortex clusters" near the airfoil leading edge induced by plasma actuation play a role of virtual aerodynamic shape. The harmonic oscillation of aerodynamic force / moment is caused by the nonlinear and strong coupling effect between the dynamic vortex structure with different scales and frequencies and the plasma aerodynamic actuation.