| Flow separation control is an important issue in the field of engineering. When stall occurs on an airfoil at the high angle of attack, it causes a drastic decrease in lift and huge increase in drag. The present work aims to investigate the mechanism responsible for flow reattachment on a NACA 0015 airfoil under the control of sawtooth dielectric barrier discharge (DBD) plasma actuator.A DBD plasma actuator was mounted at the leading edge of airfoil model to :ontrol a separated flow at a post stall angle of attack of 16° for a free-stream velocity of 6 m/s (Re= 7.7×104). Two plasma actuators were tested; straight-edge plasma actuator and sawtooth plasma actuator. Unlike the straight-edge plasma actuator with a aniform dielectric discharge, the sawtooth plasma actuator can produce the periodically intermittent discharge along the edge of the exposed sawtooth electrode. The PIV results illustrated that the sawtooth plasma actuator can produce significant disturbance which may interact with the separated shear layer and promote momentum transfer from the external flow to the boundary layer, thus forcing the flow reattachment to the airfoil surface. Then the effects of unsteady sawtooth plasma actuator on lift were studied. Compared with the steady plasma actuation, the aerodynamic performances can be enhanced with the unsteady plasma actuation; that is the maximum lift coefficient is increased by about 14% instead of 9%. The reduced frequency coincides with the natural shedding frequency of the separated shear layer was found to be more effective for increasing lift. In the last part, a novel DBD plasma actuator (hereafter called inner-semi-circle plasma actuator) was also developed aiming to enhance the flow separation control. The inner-semi-circle plasma actuator consisted of two electrodes with inner-semi-circle upper electrode and straight lower electrode. Through PIV and friction line visualizations, it has been discovered that the actuator produced well-organized counter-rotating vortices in streamwise direction with stable spanwise spatial distribution and maximum vorticity can be up to 1000 s-1. |
