Evaluation of Low Reynolds Number Turbulence Models for an Open-Channel Flow over a Rough Bed Using LES Data

There are quite a few studies investigating low Reynolds number turbulence models for predicting the near-wall flow over smooth walls. However, analogous work over rough walls is sparse despite the fact that many flows of practical interest, particularly in geophysical flows and hydraulic engineering, are over rough walls. This paper presents a priori and a posteriori evaluations of low Reynolds number Reynolds-averaged Navier-Stokes (RANS)-based modeling approaches for flows over rough walls with the help of high-resolution large-eddy simulation (LES) data. The LES data allow the calculation of the vertical distribution of the turbulent kinetic energy, the dissipation rate, the specific dissipation rate, and the turbulent eddy viscosity, so that the assumptions inherent of RANS-based turbulence models can be tested a priori. A posteriori testing of the models through RANS simulations showed that the three low Reynolds turbulence models evaluated in this paper provide a fairly accurate prediction of the velocity profile, turbulent eddy viscosity, and wall shear stress. (C) 2013 American Society of Civil Engineers.