Experimental investigation of the flow structure in the horseshoe vortex region of a circular cylinder at different rotation rates

The flow characteristics in the horseshoe vortex region of a circular cylinder mounted on a fixed flat plate were experimentally investigated using Particle Image Velocimetry (PIV) at Re = 2500, for dimensionless rotation rates (α) of 0, 0.85, 1.71, 2.56, 3.41, and 6.83. Contours of time-averaged vorticity, streamlines, streamwise and vertical velocity components, velocity fluctuations, Reynolds stresses, and turbulent kinetic energy were obtained. The modification of the horseshoe vortex structures in the rear region of the rotating cylinder under the Magnus effect was examined at different rotation rates. The present study provides a combined assessment of rotation rate, horseshoe vortex dynamics, and momentum redistribution, which remains relatively limited in the literature on wall-mounted circular cylinders. Steady cylinder rotation was found to be an effective active flow-control parameter in the horseshoe vortex region. In particular, within the fixed-Reynolds-number conditions examined here (Re = 2500), the rotation rate is found to exert a strong, first-order influence on the horseshoe-vortex flow structure; since Reynolds number and the other governing parameters were not varied in this study, this influence is thought to reflect a local result for the present dataset rather than a general ranking of rotation rate against these parameters.