Numerical Simulation For Local Scour Around Bridge Piers And Abutments

Bridge local scour is one of the major causes of bridge failure. Prediction of the maximum depth and shape of the local scour hole plays an important role in bridge design and maintance.In recent decades, researchers obtained extensive scour data through a large number of site-observations and physical model tests, and some widely used empirical formulas were presented based on those researches. However, the accuracy of these formulas is still questionable, since the predicted maximum depths of the local scour hole quite different between them.As to present a reasonable prediction of local scour around bridge piers and abutements, this paper focuses on a novel numerical method based on the computational fluids dynamics (CFD). The major work and conclusions are as follows:1) The widely used empirical equations for bridge local scour are reviewed. The predicted results for real bridge engineering with different equations are compared. It is found that highly different results are presented.2) The k-εturbulent model combined with wall function is employed in FLUENT to carry out three-dimentional numerical simulations around bridge piers and abutments. Complex flow fields and the shear stress distribution are exhibited. Based on bed load transport model, a UDF code is developed to calculate the instantaneous change of the river bed elevation. A scour simulation program is developed in C++ language, which contains FLUENT calling module and the moving grid module. FLUENT playing as a subroutine in the simulation program is called in every time step to compute the change of the river bed elevation. Secondary development on Gambit (a mesh generating platform) is carried out and Gambit is made to have a function of generating layer-by-layer mesh system. Theσmoving grid module is programmed, so the change of grid coordinations can be obtained and the mesh in the computational domain can be updated. It is found that theσmoving grid module can successfully trace the changed river bed. The present method can effectively predict local scour around bridge piers and abutments.3) Taking a bridge pier scour experiment and a bridge abutment scour experiment as simulation objects, the depth, the shape and the flow fields of scour hole were calculated. Numerical results have a good agreement with the experimental results. Especially, it achieves satisfactory results on the key issure of the maximum scour depth.4) Commonly used scour protection methods are introduced in detail. Advantages, disadvantages and the protection mechanism of each method are reviewed. Numerical simulations on slotted pier are carried out and the mechanism of this protection method is presented.