Vortex tubes in the wave bottom boundary layer

Abstract

The cause of sediment suspension events during flow reversal under waves in the nearshore is not well understood. Vortex tubes and horizontal pressure gradients have been suggested to be the cause of the suspension events. A medium sized wave flume experiment has been conducted to give insight in the hydrodynamics of the wave bottom boundary layer over a fixed single-barred profile. Flow measurements were made with PIV and the swirling strength of the velocity fields were analyzed. Around flow reversal vortex tubes were identified. The vortex tubes had similar size and swirling strength as vortices generated by vortex shedding over a rippled bed. Therefore, vortex tubes under waves in the nearshore could explain the sediment suspension events around flow reversal.