FLOW PAST A CYLINDER CLOSE TO A FREE-SURFACE

Flow past a cylinder beneath a free surface gives rise to fundamental classes of near-wake structure that are distinctly different from the wake of a completely submerged cylinder. A central feature is the gene ration of a vorticity layer from the free surface due to : localized s eparation, in the form of small-scale breaking of a free-surface wave; or complete separation from the free surface. This vorticity layer ap pears adjacent to a layer from the surface of the cylinder, thereby fo rming a jet-like flow. It is shown that the instantaneous vorticity fl ux on either side of this jet is rapidly balanced immediately after th e onset of separation from the free surface.