Local Scour by a Deeply Submerged Horizontal Circular Jet

This study investigates local scour caused by a deeply submerged circular jet. Both a wall jet and an offset jet were used in the experiments with uniform cohesionless sediments making up the bed. Experiments conducted in both air and water show that the densimetric Froude number, F_o, is the main characteristic scouring parameter in the correlation of the maximum equilibrium scour dimensions. For an offset jet, the offset distance y, which is the vertical distance between the undisturbed bed level and the center of the jet, also affects the scour hole dimensions. A higher y causes the formation of a smaller scour hole because most of the energy is diffused into the flow instead of being used to erode the sediment. For the same F_o value, the size of the scour hole is consistently smaller for tests conducted in water than in air. The reason is attributed to the formation of a sediment ridge at the downstream end of the scour hole. Due to the density difference between air and water, the ridge height is markedly different in the two flow media.