Vortex ring dynamics at a free surface

Abstract

The results of a flow visualization study of the evolution of vortex rings near a free surface are presented. The vortex rings were formed underwater with their axis parallel to the free surface one ring diameter below the surface. It is shown that vortex lines in the ring open during the interaction with the surface. The resulting flow field consists of vortex lines, beginning and terminating at the free surface. Data are reported on several features of the vortex ring evolution, which show a large reduction of the propagation speed and an oscillation of the vortex eccentricity as it propagates downstream after the interaction.