Some aspects of near-surface vortices

An experimental investigation of the dynamics of near surface vortices is presented. Using digital particle image velocimetry, the velocity and vorticity fields of a vortex ring and a pair of undulated vortices were mapped as they rise toward a free surface. Circulation measurements indicate that vortex disconnection and appearance of the surface-normal vortices are simultaneous. Vortex disconnection due to the vorticity flux through the surface is shown to be related to the free-surface deceleration