Experimental study on the cyclical jet-flipping in the wall jet scour hole

The present laboratory study used particle image velocimetry (PIV) to measure transitional flow regimes during the jet-flipping process, which is cyclical in the scour hole downstream of a sluice gate with an apron. The transitional vortical structures during jet flipping (both upward and downward) are clearly captured and discussed. Various vortices are formed in the scour hole by two pairs of component jets resulting from the impingements of jet on the bed and on the water surface, respectively. Jet-flipping always involves opposite developments of the major vortex and the bed vortex with the two impingement points moving in opposite directions along the bed and the water surface cyclically. Also, the kinetic energy of the issuing jet is dynamically distributed across the vortices which transform interactively in terms of their location, size and magnitude during jet-flipping, as indicated by the distributions of average kinetic energy (AKE) and spanwise vorticity.