Transitory Separation Control over a Stalled Airfoil

Transitory attachment of the flow over a stalled, 2-D airfoil is investigated in wind tunnel experiments using pulsed actuation. The impulse of the momentary control jets is produced by combustion based actuators on characteristic time scales O[1 ms] that are an order of magnitude shorter than the convective time scale of the flow. A single actuation pulse results in transitory flow attachment that is manifested by rapid increase in the global circulation and aerodynamic forces and persists for about ten convective time scales before the flow becomes fully stalled again. Large-scale changes in vorticity accumulation that are associated with repetitive, burst-modulated actuation pulses are exploited for significant extension of the streamwise domain and duration of the attached flow with a corresponding increase in the peak circulation. High-resolution PIV measurements of the interaction between the pulsed jets and the cross flow reveal details of the severing and collapse of the separated flow domain and the dynamics of vorticity accumulation within the attaching boundary layer.

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