Modelling plane open-channel flows by coupled depth-averaged and RANS equations

Abstract

Herein, a coupled depth-averaged (DA) and Reynolds-averaged Navier–Stokes (RANS) model is developed for steady plane open-channel flows with or without the assumption of hydrostatic pressure (HP). Initially, the water surface and the DA velocity are estimated using a DA model by neglecting non-uniform velocity (NUV) and non-HP (NHP). Then, in the RANS model, the horizontal momentum and the continuity equations are solved for the horizontal and vertical velocity components, respectively, with the water surface as a fixed zero-pressure boundary. For the non-hydrostatic RANS model, the pressure Poisson equation is solved for NHP. A correction term is introduced in the Reynolds horizontal momentum equation for mass balance. Once the RANS model results are available, the DA model results are updated iteratively by incorporating the effects of NUV and NHP. The agreement between the model and experimental data is quite satisfactory along with an excellent computational efficiency.