Control of Unsteady Aerodynamic Loads on a Pitching Airfoil using Pulsed Bleed Actuation

The aerodynamic loads on a dynamically pitching 2-D airfoil (Re_c = 6.3∙10⁵) are regulated temporally in wind tunnel experiments without moving control surfaces or an auxiliary air supply using impulsive (~4 convective time scales) bleed air flow. The distributed bleed is driven through surface ports and the airfoil interior by pressure differences between the suction and pressure surfaces and regulated using low-power louvers integrated into the airfoil surface. It is shown that bleed actuation pulses synchronized to the time-periodic pitch cycle at prescribed phases enable programmable, temporal variation of the aerodynamic loads on time scales comparable to the convective time scale of the cross flow. Bleed actuation through ports near the leading edge (0.8% of planform open area) enhances flow attachment at high angles of attack and mitigates dynamic stall with a lift increase of up to ~25% and commensurate changes in pitching moment and lift hysteresis. Phase-averaged PIV measurements of the flow field over the airfoil suction surface and in its near wake in the presence of single and multiple actuation pulses during the pitch cycle reveal dynamics of temporal cyclic variations in attachment and unsteady circulation.