Pressure Distribution around a Rotating Cylinder near the Critical Reynolds Number

Abstract

The pressure distributions on the surface of a circular cylinder rotating in a uniform flow were measured near the critical Reynolds number in a low speed wind tunnel. In the subcritical region, when the spin parameter is increased, the average pressure coefficient on the side of the higher relative velocity decreases suddenly at the critical spin parameter, so that the lift force decreases from the maximum to the minimum value. The separation point on this side oscillates violently downstream and upstream. With further increase in the spin parameter, the separation point moves downstream. The pressure distribution in every one rotation varies so randomly near the critical spin parameter that the average lift force decreases continuously to the minimum value. In the supercritical region, the average pressure coefficient on the side of the lower relative velocity increases suddenly at the critical spin parameter, and the separation point on this side moves suddenly to the upstream direction. The movement of the separation point is more rapid than in the case of the subcritical region. As the result, the lift force decreases discontinuously from the maximum to the minimum value.