Experimental Investigation of Air Jets to Control Shock-Induced Dynamic Stall

This paper shows experimental results for dynamic stall control on a dynamically pitching OA209 airfoil at Mach 0.5, with Reynolds numbers 1.9 × 10⁶ and 0.85 × 10⁶. The control was by supersonic constant blowing on the suction side of the airfoil. Dry compressed air was blown normal to the airfoil chord, from portholes at 10% chord, with diameter 1% chord. At both Reynolds numbers, the OA209 without blowing experienced shock-induced stall with a hysteresis in lift and pitching moment around the static values, rather than the overshoot in forces typically associated with a dynamic stall vortex. The forces and the stall control were primarily functions of the maximum angle of attack, with full control of stall possible for maximum angles of attack of 14° and less. The higher Reynolds number required relatively more blowing (higher C_q , C_μ ) to control the dynamic stall. Drag was reduced for separated flow, but the energy required in compressed air to achieve this was more than the savings in drag, and no cases were found in which flow control resulted in a reduction in total power used. Increasing the jet spacing resulted in equivalent flow control with less air use. Jets spaced at 20% chord and mass flux ratio C_q = 0.004 (momentum ratio C_μ = 0.016) resulted in a reduction of the pitching moment peak by 60%. The flow control with air jets was uncritical regarding the aerodynamic damping.