Aero-Effected Control of a Pitching Airfoil by Bleed Actuation

The aerodynamic forces and moments on a static and a dynamically pitching 2-D airfoil model are controlled in wind tunnel experiments using distributed active bleed. Bleed flow on the suction surface downstream of the leading edge is driven by pressure differences across the airfoil surfaces and is regulated by low-power louver actuators. The bleed interacts with cross flows to effect time-dependent variations of the vorticity flux and thereby alters the local flow attachment, resulting in significant changes in lift and pitching moment at static preand post-stall angles (over 50% increase in baseline post-stall lift). The flow field over the airfoil is measured using high-speed (2000 fps) PIV, resolving the dynamics and characteristic time-scales of vorticity production and advection that are associated with transient variations in lift. It is shown that bleed actuation can improve the lift hysteresis and negative damping characteristics during oscillatory pitching by affecting the shedding of the dynamic stall vortex and the ensuing flow attachment during the downstroke.