Control of Poststall Airfoil Using Leading-Edge Pulsed Jets

Abstract

The performance of active flow control on a NACA laminar airfoil at a poststall angle of attack of 20 deg is evaluated using discrete, wall-normal pulsed jets. The chord Reynolds number is 64,000, and actuation is implemented near the leading edge of the airfoil. For actuation periods equal to one convective period and two convective periods, the average lift coefficient increases monotonically as the actuation duty cycle is reduced, for a given blowing ratio. Flow reattachment is achieved following the termination of a short duration pulse, and the reattachment point propagates toward the trailing edge at a rate three times slower than the convective period of the flow. Extended jet off times can cause full separation to reoccur, should the reattachment point reach the trailing edge; however, optimal jet off times can cause suction pressure to extend over much of the airfoil chord. Higher duty cycle actuation results in a phase shift of the dynamics that appears to be commensurate with the duration of the jet. A disturbance initiated by the termination of the jet causes a delay in the redevelopment of the shear layer and the reattachment of the flow, prohibiting high lift values from being attained.