Effect of Confinement of Flow by Side Walls on the Cross Flow past a Circular Cylinder at Moderate Reynolds Numbers

The effect of confinement of flow over the transversal coordinate on cross flow past a circular cylinder at the Reynolds numbers from 40 to 255 (based on the cylinder diameter and the undisturbed flow velocity) is studied numerically and experimentally. In the experiments, the cylinder was located in a rectangular channel and, in the case of numerical simulation, three types of the boundary conditions, namely, the periodic boundary conditions and the slip and no-slip conditions were imposed on the side walls confining the flow. Particular attention is concentrated on the vertical flow structure in the cylinder wake. It is shown that spiral vortices that travel in the plane of symmetry of the channel are formed only in the case of no-slip boundary conditions in the region of junction of the cylinder and the side walls. Under their interaction, vortex clusters are formed in the center of channel and some indications to flow turbulization can be observed in the wake. Under the periodic boundary conditions and the slip conditions on the side walls, there are no spiral vortices and, in the Re range from 200 to 250, the A and B modes of three-dimensional instability and turbulence transition are implemented in the cylinder wake. The effect of the channel width and the type of boundary conditions on the side walls on the vortex wake structure behind the cylinder and integral flow parameters is estimated.