Hydrodynamics of Rectangular Broad-Crested Porous Weirs

Abstract

In this study, the hydrodynamics of rectangular broad-crested porous weirs were numerically simulated using a nonlinear model between the pressure gradient and flow velocity through the porous medium. Computational fluid dynamics (CFD) analysis has been performed and renormalized group (RNG) k-ϵ model is used as the turbulence closure for Reynolds-averaged Navier-Stokes (RANS) equations. Solid and porous weirs with various properties were examined, and the drag coefficients of the porous weirs in the nonlinear flow resistance model were determined using sensitivity analysis. A logarithmic equation to determine the drag coefficient directly as a function of the hydraulic permeability is presented. By performing three-dimensional (3D) numerical simulations for a wide range of the approach discharge for different porous weir models, the discharge coefficient is described as a piecewise function of related parameters, such as head over the weir, porosity, and the grain diameter of the porous weir. Moreover, for the simulated scenarios, ratios of water passing through and over the weir are determined; consequently, new equations for the discharge ratio are developed. Finally, complex flow features over and through the different porous weirs have been expounded using developed discharge ratio curves.