Investigations of dynamic stall and dynamic stall control on helicopter airfoils

Abstract

Investigations into dynamic stall and dynamic stall control on airfoils are detailed using pitching airfoil experiments and numerical investigations at Mach 0.3, 0.4 and 0.5 on the airfoils EDI-M109, EDI-M112 and OA209. Two-dimensional dynamic stall was investigated, and the effects of the wind tunnel interference, rotation and the finite wing on the three-dimensional stall process were detailed. The curvature of the stall vortex and its effect in reducing the strength of the dynamic stall compared to a two-dimensional treatment was investigated using CFD and experiments with high-speed pressure sensitive paint (PSP) and pressure transducers. Stall control was designed based on its ability to increase the lift in CFD simulations of static stall and implemented by using constant and pulsed blowing with high-pressure air jets in the vertical direction, and the stall was demonstrated to be significantly reduced at all Mach numbers investigated. Optimal mass flux and jet spacing were found for Mach 0.3 and Mach 0.5, and depended on the test case investigated. Optimums for deep stall were around Cμ =0.12 for M=0.3 and Cμ =0.02 for M=0.5. Pulsed blowing was found to be at best as effective as constant blowing with the same mass flux, for the jet configuration and test cases investigated. Flow control by blowing reduced drag 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.