Vortices behind a submerged cylinder in a rotating system

We experimentally studied the wake flow behind a submerged vertical cylinder in an open channel rotating at a constant angular velocity around a vertical axis. We obtained the two-dimensional velocity field on the free surface of fluid by a Particle Image Velocimetry measurement. In some cases, we found the emergence of a steady vortex perpendicular to the surface and vortex-shedding behind it. The necessary condition for the emergence of such vortices is given by the excess of Rossby number below a critical value, which is determined by the relative height of the cylinder. Reynolds number must be large enough, and the thresholding value depends on the relative height.