Vortex kinematic around a submerged plate under water waves. Part I: Experimental analysis

This paper presents the vortex dynamics generated by the interaction of a submerged horizontal plate, considered as a vortex generator, and a monochromatic wave. The velocity and vorticity fields are determined experimentally using PIV technique for different resolutions in order to study the global flow around the plate and the formation and advection of vortices upstream and downstream of the plate. The global flow around the plate shows great discrepancies with the potential flow solution: two recirculation cells are formed beneath the plate, the global flow is non-symmetric and the advection of vortices induces strong velocities not represented by the potential flow theory. The formation of vortices at the edges of the plate is characterised. At each period, one vortex is formed at the edge followed by the formation of an opposite sign vortex. The upstream and downstream vortex pairs are then advected in front of the plate and toward the bottom respectively, over a distance of about one third the plate length. The lifetime of vortices is about two wave periods. This study will help us validate a numerical software to be used for analysing the influence of various parameters on the dynamics. These results will be presented in the second part of this paper.