The evolution of the vortex street behind a rotating circular cylinder in uniform free stream is investigated numerically at high Reynolds number. The ratio of the cylinder surface velocity to the free stream velocity, α is in the range 0 ≤ α ≤3 The method used to calculate the flow can be considered as a combination between the diffusion-vortex method and the vortex-in-cell method. The lift and drag forces exerted by the fluid on the cylinder surface as well as the Strouhal number of vortex shedding, are determined together with the flow patterns in the wake. It was found that the vortex shedding and wake development behind the cylinder vary significantly depending on the magnitude of the rotation parameter α. When α = 2, the vortex street behind the cylinder in the near-wake inclines as a whole towards the direction of rotation as α increases The Kármán vortex street structure begins to deteriorate as soon as α exceeds 2 and finally disappears for α =3.
Flows past a rotating circular cylinder have been tine subject of constant study since the middle of the last century because of the intrinsic complexities and practical importance of these flows. It is well known that when a non-rotating cylinder is subjected to a uniform flow, the separation of the boundary layers usually occurs. The separated boundary layers normally roll up into vortices at a fairly constant frequency. However, when a rotating circular cylinder is placed in an uniform flow, the separation of the boundary layers as well as the vortex shedding frequency depend significantly on the ratio of the cylinder surface velocity to the free stream velocity, α. When α is larger, a Kármán vortex street, Gōrtler-type Vortices and Taylor vortices are generated at the same time (Matsui 1981). When α is greater than a certain limiting value, Kármán vortex street disappears entirely.