Comparison of Turbulence Models for Estimation of Bed Shear Stress Around Bridge Abutment in Compound Channel

Bridge failures due to scour at bridge abutments clarify importance of flow field around them. Scope of this study is the comparison between experimental results and numerical simulation of bed shear stress around bridge abutment in a compound channel by Flow-3D model. In order to calculate the experimental bed shear stress, flow velocity was measured by a 3D electromagnetic velocimeter in different levels of flow depth of floodplain. For estimation of Reynolds stresses of u w¢ ,u¢v¢ and v¢w¢ , in low flow depth of floodplain, extrapolations of these values to the bed were used. Experimental results showed that maximum bed shear stress occurred at the upstream corner of the abutment. After mesh generation, hydraulic simulation of flow with Flow-3D model was run in 5 turbulent models of Prandtl mixing-length model, one equation turbulent energy model, k-ɛ model, renormalized group (RNG) model and large eddy simulation model. Comparison between models showed that the results achieved by the RNG model had a better agreement with experimental observations and the pattern of shear stress around the bridge abutment was well predicted by this model. Bed shear stress at the upstream corner of the abutment was determined by experimental results and RNG model giving 3.84 and 4.6 N/m2, respectively.