Experimental and Numerical Investigations of Flow over and under Weir-Culverts with a Downstream Ramp

A series of experimental and numerical studies were conducted to investigate the hydrodynamics of weir-culverts with a downstream ramp in submerged-flow condition. A comparison of the numerical and experimental results with the selected turbulent model indicated that the numerical model is capable of simulating weir-culverts with a downstream ramp with 5% error. Water surface profiles of the proposed weir-culvert models were observed in transition from free to fully submerged flow, and four flow regimes of impinging jet regime (IJR), surface jet regime (SJR), surface wave regime (SWR), and deeply submerged regime (DSR) were identified. The proposed flow regimes were classified based on the ratio of surface flow to mean downstream velocities and the ratio of tail water to headwater depths. For proper design and erosion protection of irrigation canals, hydrodynamic characteristics of the identified flow regimes such as streamwise velocity, velocity path lines, and turbulent kinetic energy (k) were extracted from experimental and numerical results. The results showed that the position of maximum k moved from the toe of the weir-culvert to the water surface as the tail water level increased. This indicated a significant reduction of energy dissipation rate due to turbulence, which necessitates proper bed protection far downstream of the structure. A comparison of weir-culverts with different weir lengths in a DSR showed higher surface jet energy dissipation and contraction coefficient of weir-culverts with larger length. The eye of the rollers and the boundaries between vortices were extracted from numerical simulations, and it was found that the stagnation points and surface jet thickness profiles moved toward the downstream side of the weir-culvert as the weir length increased. (C) 2021 American Society of Civil Engineers.