Structure of turbulent flow in scour holes downstream of submerged jets

Scouring downstream of circular jets is a common problem and some research has been conducted to assess the extent of scouring that can be expected under particular flow conditions. However, little attention has been directed towards developing an understanding of the flow structures leading to scouring downstream of jets. Research has been carried out at the University of Hertfordshire using facilities at H.R. Wallingford to explore scour downstream of jets and study the flow fields in and surrounding the scour hole, the preliminary findings are presented here. The results indicate that the initial scour hole development is a result of the jet impacting on the bed and transporting sediment out of the scour hole. Further growth in scour depth is caused by sweep events in the region of maximum scour depth. Over the dune region high contributions to the Reynolds stress are observed in all four quadrants with a dominance in quadrant 1 corresponding to outward interaction events. These events have been observed for open-channel flow over dunes downstream of the point of re-attachment and may be responsible for further sediment transport.