Abstract:
This work presents results of an experimental investigation into synchronized active flow control of a Sikorsky SSC-A09 airfoil undergoing periodic pitching motion in an unsteady free stream using leading edge blowing. The airfoil was evaluated at reduced pitching frequencies up to k=0.05 at steady Mach numbers of 0.2 and 0.4, and at k=0.025 with phase-locked pitch and Mach oscillations at Mach 0.4±0.07 at Reynolds numbers from 1.5 to 3 million. A spanwise row of vortex generator jets (VGJs) located at 10% chord is fed by an oscillating valve that is phase-locked to the pitch oscillation of the airfoil. The oscillating valve can be set to produce a peak jet mass flux ratio (Cq) of 0.0022 or 0.0028 with a background Cq of half this value over the remainder of the period. The phase and duration of the peak Cq were varied to optimize the flow control benefits to both CL and CM hysteresis loops and reduce negative damping. Peak performance was observed with actuation initiated just after lift stall and continuing for 11% of the pitch cycle. Blowing beyond 11% resulted in no perceptible benefit. Compared to steady blowing flow control, the 11% synchronized control case delivers comparable (or better) performance with less than 50% of the massflow. The degree of stall control is a function of reduced frequency, mass flux ratio, and Mach number.