SINOPSIS

Controlled flow transients that are associated with sequenced separation and reattachment of the flow over a stalled airfoil are exploited for aerodynamic performance enhancement beyond controlled conventional quasi-steady post-stall attachment. Actuation is effected by synthetic jet actuators that are operated at frequencies are typically an order of magnitude higher than the natural frequency of the base flow. This approach to aerodynamic flow control is based on earlier observations by the authors that controlled post-stall reattachment or imposed stall by the termination of the actuation are accompanied by large transitory changes in the circulation about the airfoil before a quasi-steady level is reached. Pulsed modulation of the actuation waveform is exploited to accumulate vorticity during the initial stages of the separation process and thus to increase the lift (similar in principle to dynamic stall).