Dynamic Stall Control by Passive Disturbance Generators

Kurzfassung

Passive cylindrical disturbance generators mounted near the leading edge of an airfoil significantly improved its performance under dynamic stall conditions. Time resolved particle image velocimetry and simultaneous pressure measurements were conducted at mid chord of a pitching airfoil equipped with passive disturbance generators. The disturbance generators were effective in reducing the strength of the dynamic stall vortex and therefore the negative pitching moment peak and hysteresis effects. When disturbance generators were applied, the flow separation type was altered from leading to trailing edge stall. In contrast to the clean case, reattachment was initiated immediately after the separation reached the leading edge region. Besides the circular shape, also backward and forward wedge shaped disturbance generators were investigated. While the backward wedge also showed favorable results, the forward wedge were less successful. The shape appears to have a strong influence on the effectiveness of reducing the negative impact of dynamic stall, depending on the sense of rotation of a pair of weak trailing vortices.