Advance Ratio Effects on the Dynamic-stall Vortex of a Rotating Blade in Steady Forward Flight.

摘要

The effect of advance ratio on the flow structures above a rotor blade in dynamic stall is studied using stereoscopic particle image velocimetry. The dynamic stall vortex shows a significant velocity component in its core, implying a helical structure progressing radially outboard. The radial velocity attenuates at outboard locations, in contrast to the expected increase with centripetal acceleration. This attenuation is accompanied by an increase in unsteadiness of the vortex. The unsteadiness shows a low-frequency cycle-to-cycle variation despite steady freestream conditions and blade tracking. Proper orthogonal decomposition analysis of the dominant flow mode confirms the unsteady behavior of the leading-edge vortex. The dependence on advance ratio is used to relate the stability of the dynamic-stall vortex to Coriolis effects.