Mitigation of dynamic stall over a pitching finite wing using high-frequency actuation

Abstract

A novel high-frequency flow control strategy for mitigation of dynamic stall is demonstrated for the case of a finite wing using high-fidelity wall-resolved implicit large-eddy simulations. A NACA 0012 wing of aspect ratio AR _ 4 is considered at freestream Mach number M∞ = 0.1 and chord Reynolds number Rec = 2 × 105. The wing undergoes an oscillatory pitching motion with reduced frequency k = π∕16 and maximum angle of attack αmax = 22°, resulting in deep dynamic stall for the baseline case. Very-high-frequency (Stf = fc∕U∞ = 50.0) spanwise uniform lowamplitude pulsed forcing is imparted through a zero-net mass flow blowing/suction slot located on the wing lower surface near the leading edge. The imposed small fluctuations are amplified by the laminar separation bubble (LSB) and inhibit LSB bursting and the formation of large-scale dynamic stall vortices. By maintaining effectively attached flow throughout the pitching cycle, actuation provides a significant reduction in the cycle-averaged drag and in the force and moment excursions. In addition, the negative (unstable) net-cycle pitch damping found in the baseline case is eliminated.