Control of Dynamic Stall on a Pitching Airfoil using Pulsed Bleed Actuation*

The aerodynamic loads of a dynamically pitching 2-D airfoil (Clark-Y, Re_c = 6·10⁵) are regulated without moving control surfaces by impulsive (~4 convective time scales) pulsed air bleed actuation driven by pressure surface differences through the airfoil interior.  The bleed air is driven through spanwise arrays of ports near the leading edge (0.12% of planform open) and regulated using integrated louvers controlled at prescribed phases relative to the time-periodic pitch cycle. Despite its short duration, the low-impulse bleed actuation leads to large-scale changes in the flow around the airfoil and consequently to significant temporal variations in the lift and pitching moment and specifically to mitigation of dynamic stall, with an increase of up to 30% in maximum lift and commensurate reductions in lift and moment hysteresis.  Phase-locked PIV measurements of the flow field over the airfoil and in the near wake during dynamic pitch explore the temporal cyclic variations in flow attachment and circulation that are associated with the corresponding changes in the aerodynamic loads.