Passively adaptive control of flow over a sphere for drag reduction at high Reynolds numbers

Abstract

Previous passive flow control methods have limitation in that their drag-reducing effectiveness depends on the Reynolds number. In the present study, a new passive control method (AMR: Adaptive Moving Ring) is devised to reduce drag on a sphere with no Reynolds-number dependence at high Reynolds numbers of Re=0.5×10^5−5.2×10^5 and tested through the wind-tunnel experiment. AMR adaptively changes its size depending on the wind speed (i.e. Reynolds number) without the energy input, showing more drag reduction than other fixed-sized passive devices such as surface roughness and dimples for most of the Reynolds number range tested. AMR, however, has limitation in that its drag-reducing effect depends on the flow direction.