Dynamic Stall Control by Passive Disturbance Generators

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Dynamic Stall Control by Passive Disturbance Generators

Heine, Benjamin / Mulleners, Karen / Joubert, Gilles / Raffel, Markus

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 the midchord 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 the 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. In addition to the circular shape, also backward- and forward-wedge-shaped disturbance generators were investigated. Although the backward wedge also showed favorable results, the forward wedge was less successful. The shape of the disturbance generators 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.