Reynolds-averaged Navier-Stokes modeling of submerged ogee weirs

The present study documents the successful application of a Reynolds-averaged Navier-Stokes model with conventional turbulence closure to calculate discharge coefficients for submerged flow conditions at ogee-type weirs. The flow pattern downstream of submerged weirs is complex. At low submergence, there is a plunging jet and submerged hydraulic jump. At higher levels of submergence, the jet detaches from downstream of the crest and develops toward the free water surface. The results presented are of particular interest to the hydraulic engineer because they demonstrate that reliable results for the complex flow problem are achieved, but only with the use of a fine computational mesh. It is well known that the results of computational fluid dynamics (CFD) models are strongly mesh dependent, but extensive sensitivity analysis is often time-consuming and costly. Therefore, engineering practice relies on cases that have been tested extensively. For the mesh resolution, the present study recommends a nondimensional number that can be used as a reference for modeling flow over weirs. An important result for hydraulic engineering applications is that the minimum mesh resolution for submerged flows is completely different compared to nonsubmerged flows. The simulations are compared to physical experiments from the literature. With sufficient mesh resolution, an average relative error in capacity of 2% across the simulations is achieved for the finest mesh resolution compared to physical experiments.