Transition from deep to shallow water layer: formation of vortex dipoles

In this paper we study the transition from a deep to a shallow water layer and the formation of quasi-two-dimensional vortex dynamics. Vortices are experimentally generated by a circular horizontal turbulent pulsed jet. The dimensional analysis gives two relevant dimensionless parameters: the jet Reynolds number Re and a number C which characterizes the vertical confinement. They are respectively defined by Re=Q/ν and C=(Q/H2)tinj (H is the water depth, ν is the kinematical viscosity, Q the injected momentum flux and tinj the injection duration). Experimental results show a strong influence of C on the flow: when C<1, the evolution is a typical three-dimensional turbulence decay, while when C>2 we observe the formation of large vortex dipoles. However these dipoles are not strictly two-dimensional because of the presence of a vertical circulation in the front of the dipole. Results are independent of the jet Reynolds number in the range 1000