Effects of Time-Varying Flow Velocity on Steady Blowing Flow Control for a Pitching Airfoil

This work presents results of an experimental investigation into the effect of time-varying free stream on active flow control of a Sikorsky SSC-A09 airfoil undergoing periodic pitching motion using supersonic, leading edge vortex generator jets. The airfoil was evaluated at reduced pitching frequencies of k=0.026 to k=0.05 at Mach 0.4+0.07cos(ωt) at a mean Reynolds number of 3.0x10⁶. A spanwise row of vortex generator jets located at 10% chord blowing at a jet mass flux ratio (Cq) of 0.001-0.005 demonstrated improvements in both CL and CM hysteresis loops and reductions in negative damping. Initial data indicates that the interaction between VGJ blowing and a time-varying flow delays flow separation during the pitch-up and accelerates flow reattachment during the downstroke. Post-stall shear layer instabilities and airfoil load oscillations are amplified. The VGJ interaction with the shear layer results in an increase in aerodynamic performance determined by the surface pressure taps and illustrated by the use of Background Oriented Schlieren (BOS) as a flow visualization technique.