Influence of rotation on dynamic stall

Kurzfassung

A computational investigation of the effect of rotation on two dimensional deep dynamic stall has been undertaken, showing that the effect of rotation is to reduce the severity of the pitching moment peak and cause earlier reattachment of the flow. A generic single blade rotor geometry was investigated, which had a pitching oscillation around the quarter-chord axis while in hover, causing angle-driven dynamic stall. The results at the mid-point of the blade have the same Mach number (0.31), Reynolds number (1.15e6) and pitching motion alpha=13°plusminus7°) as the DS2 dynamic stall test case for which significant experimental wind tunnel data and 2D computations exist. The rotating blade is compared with 2D computations, and computations using the same blade without rotation at Mach 0.31 and with the same pitching motion. All test cases involve geometries propagating into undisturbed flow with no downwash. The 3D grid computed without rotation had lower lift at the reference section than for a 2D computation, and the lift overshoot classically observed for Spalart-Allmaras turbulence models during 2D dynamic stall was not present in the 3D case. Rotation reduced the strength of the dynamic stall vortex, which reduced the accompanying pitching moment peak by 25%.