Numerical Simulation On Local Scour At Downstream Of Submerged Constructions

As a previous work of studying the local scour at bridge pier, a vertical 2-D k -εturbulent model is used to simulate the flow field of flow meeting submerged constuc-tions and the equilibrium profile of local scour at downstream of submerged constructions. Local scour occurs when bed shear stress of flow is higher than or equal to critical bed shear stress for sediment incipient motion according to Shields curve.The model is applied to predict the flow in a channel where submerged constructions constrict flows in different proportions. The results computed and predicted have been given for velocity field, local vortex zone, maximum-depth position estimated by critical shear stress and range of local scours on flat bed nearby submerged constructions, which are reasonable by analysis. A small-size vortex forms at downstream of submerged constructions when constriction proportion is less than 50% and vortex is not the main reason leading to bed local scour. The vortex zone extends larger as constriction proportions increase and vortices come to be the main effects of bed local scour.Moreover, a method of fitting moving boundary with premeshed rectangular grid lines is proposed in this paper to deal with the changing bed as scour developing. Employing this method, the equilibrium profile of local scour at downstream of submerged constructions which constrict flows in 50% is simulated. The calculation results agree well with the law. It shows that this method performs efficiently for moving boundary problems.