Boundary Layer Effects on Hydraulic Jump Location

The rate of displacement of the toe of a hydraulic jump along a channel with respect to change in tailwater elevation is defined as the position sensitivity of the jump. The steady flow downstream of a model sluice gate is analyzed theoretically for the case of a laminar boundary layer developing from the vena contracta and breaking into fully developed turbulent flow. It is shown that the position sensitivity of the jump is dependent upon Froude number, boundary roughness and distance downstream from the gate. Experiments have been performed using a shallow stream of depth 0.26 in. (4.064 mm). The theoretical analysis is justified and the jump is shown to be much more sensitive in a laminar boundary layer development region than in a fully developed turbulent flow. In general, sensitivity is greater in laminar than turbulent flow, is decreased by an increase in boundary roughness and by an increase in Froude number. Because model tests are at a lower Reynolds number than corresponding full scale situations, model results for jump sensitivity are conservative.