CFD study of decay function of wall shear stress with scour around complex-shape bridge pier

Pier scour problem is close related to the safety of bridges. The Federal Highway Administration of the United State also has a great interest in studying the relation between hydraulic loadings and scour depth. The current technological problem of directly measuring hydraulic loadings on a dynamic bed using physical experiments and the weak capacity to simulate the real scour processes with CFD methods inspired the development of a hybrid approach by combining them to study pier scour. This research specifically focuses on the CFD part of the hybrid method. A series of three-dimensional (3-D) CFD models were developed with unsteady Reynolds Averaged Navier-Stokes equations and the k-ϵ turbulence model to calculate wall shear stress distributions around piers under different kinds of flow conditions. These CFD models were verified and calibrated by comparing wall shear stress distributions with other CFD simulations, which use a DES turbulence model. The CFD simulation results were applied to develop a decay function of dimensionless wall shear stress with relative scour depth. Combined with the previous physical experimental data, the decay function was updated to be an envelope function to more accurately describe the decay trend. The results of CFD modeling for water flows around a rectangular pier with a 30° attack of angle were used to verify the decay function and the envelope function. With surveyed full-scale bathymetries of the Feather River Bridge, this hybrid approach and the decay function were applied to study the pier scour problem. The decay trend and the envelope decay function were verified with the results of CFD modeling for the full-scale models. Using the soil composition of each layer, the application of the decay function was preliminarily developed