HYDRAULIC JUMPS, FLOW SEPARATION AND WAVE BREAKING - AN EXPERIMENTAL-STUDY

We describe experimental results on the circular hydraulic jump in a v iscous fluid (ethylene-glycol mixed with water) in a setup, where the depth of the fluid far away from the jet is controlled. On increasing the depth, we find a transition from a state (type 1) with separation occurring only on the bottom, to a state (type 2) with a ''roller'', i .e. separation occurring also on the free surface, as in a broken wave . The system is laminar both before and after the transition and can t hus be very accurately controlled. We present data for the height prof ile of the fluid layer, for the surface velocity and for the location of the separation points. Further, we show direct numerical simulation s of the Navier-Stokes equations confirming our interpretation of the transition.