Unsteady Aerodynamics - Synchronized Flow Control of Dynamic Stall under Coupled Pitch and Freestream
Technical Report,01 Jun 2015,30 Apr 2016
Ohio State University Columbus United States
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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 k0.05 at steady Mach numbers of 0.2 and 0.4, and at k0.025 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 percent 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 percent of the pitch cycle. Blowing beyond 11 percent resulted in no perceptible benefit. Compared to steady blowing flow control, the 11 percent synchronized control case delivers comparable or better performance with less than 50 percent of the massflow. The degree of stall control is a function of reduced frequency, mass flux ratio, and Mach number.