Numerical Investigation of Turbulent Open Channel Flow with Semi-cylindrical Rough Beds

Flow development in an open-channel with rough beds was investigated using FLUENT, a commercial Computational Fluid Dynamics (CFD) software. The Renormalization Group (RNG) k-ɛ turbulence model was used for subcritical flow cases. The Volume of Fluid (VOF) method was used to allow the free-surface to deform freely with the underlying turbulence. The main purpose of this study was to examine the effects of the different types of surface roughness on a turbulent boundary layer in a relatively high Reynolds flow. The determination of velocity profile in turbulent open channels with rough bed is a difficult task due to the significant effects of the roughness. The velocity distributions in the log-region for the rough wall were determined. The roughness function ΔU +, the characteristic downward shift of the logarithmic part of the mean velocity profile, was found to be more than 12 for three rough surfaces the roughness function, ΔU + scales logarithmically with normalized effective height y+.