Numerical Investigations Of Flow Characteristics Around Spur Dikes In An Open Channel

Spur dike structures are widely used in hydraulic engineering,by constructing series of spur dikes perpendicular to the river banks,and as a result,the flow is kept away from the erodible banks,at the same time the laterally confined flow attains a sufficiently high velocity to keep the navigation channel at the proper depth. This paper is concerned with the flows around spur dikes.We established a 3D model with free surface, which is based on unstructured meshes. We employed finite volume method(FVM) to discretize the governing equations and a one equation S-A turbulence model was used to simulate the turbulent flow.Firstly,for study cases with different Fr number,we analyzed the flow structures near an emerged spur dike perpendicular to the side wall,discussed the formation of the vortex system at the base of the spur dike and described the spatial and temporal evolution of HV system.The analysis was focused on predicting the length and width of the recirculation zone,the variation of bottom friction and the evolution of the mixing layer generated by the main and groin flows.Secondly,for study cases with different Fr number,we analyzed the flow structures near two emerged spur dikes,especially the flows in groyne fields, and discussed the formation of the vortex system at the base of the first spur dike and described the temporal and spatial evolution of HV system. The attentation was again put on the predictiong of the length and width of the recirculation zone,the effect of Fr number to the flow patterns in the groyne field,the characteristics of bottom friction,the 2D large coherent structures(2DLCS)at the free surface,and the development of the mixing layer generated by the main stream and groyne flows. The mass exchange between the main channel and groyne field was analyzed by means of simulating the transportation of a passive tracer.