Hydrauic jumps in a channel crossing - A Numerical Approach

Flooding in a street network may occur under an extremely heavy rainfall. The determination of flow distribution in street networks thus is important for the design of flood protection measures. The junction of streets is generally a cross and the flow there is highly three-dimensional. If the slopes of the streets are steep, the inflows will be supercritical and hydraulic jumps will occur close to the junction. To reduce the degree of empiricism, a 3D RANS (Reynolds Averaged Navier-Stokes equation) model has been implemented in this study to investigate the steep flow phenomena in a channel crossing. The numerical model utilizes the split-operator approach, in which the advection, diffusion and pressure propagation are solved separately. The free surface elevation is determined by solving the vertically integrated mass conservation equation. The numerical model has been validated for the case of a hydraulic jump in an open channel. The model is then applied to simulate the flow in a channel crossing. The results reproduce the hydraulic jump and hydraulic drop phenomena and predict accurately the relationship between the input power ratio and the outflow discharge ratio of the channel crossing.