Blowing Flow Control of Dynamic Stall under Coupled Pitch and Freestream Oscillations

This work presents results of an experimental investigation into active flow control of a Sikorsky SSC-A09 airfoil undergoing periodic pitching motion in an unsteady free stream using steady, supersonic, leading edge blowing. The airfoil was evaluated at reduced pitching frequencies up to k=0.075 at steady Mach numbers of 0.2 and 0.4, along with phase-locked pitch and Mach oscillations at Mach 0.4±0.06 at Reynolds numbers from 1.5 to 2.9 million. A spanwise row of vortex generator jets (VGJs) located at 10% chord blowing at a jet mass flux ratio (Cq) of 0.0029-0.0040 demonstrated improvements in both CL and CM hysteresis loops and reductions in negative damping. The degree of stall control is a function of reduced frequency, mass flux ratio, and Mach number. Phase-locked Mach oscillations impede stall control at low reduced frequency but facilitate stall control at higher reduced frequency when compared to steady Mach conditions with constant blowing.