Experimental Study And Numerical Simulation On The Flow Characteristics Of Cutting The Beach In Bridge Area

For crossing-river bridge projects,most of which occupy the river flow cross section.The original flow structure is changed by bridge piers.It will result in adverse effects on bridge,embankment and the flow capacity.In the engineering practice,the river section compensation is usually carried out by cutting the beach and dredging.There are many factors to be considered on reasonable compensation scheme.At present,there are few research results and the engineering practice is mainly based on experience.It is very meaningful to carry out the experimental study on the flow capacity and numerical simulation.Based on physical model test and numerical simulation,several factors influencing river flow capacity are studied,including compensation area,beach slope ratio,dredging depth,dredging border slope ratio.The physical model test is based on the generalized double straight stream model,and the flow characteristics of different conditions around the piers are analyzed.The relationship between the flow capacity of the river section compensation and other factors are studied.A three-dimensional numerical model for the water resistance of single pier in bridge area is established by Fluent.The turbulence model is based on the standard k-e two-equation model.The governing equation of the fluid motion is discretized based on the finite volume method.The VOF method is used to track the free surface.The wall function method is used to solve the flow in the wall region.The characteristics of the river flow and the flow capacity of the river section compensation are analyzed in different conditions.The results are compared with the experimental results,and the main conclusions are as follows:(1)The experimental of the flow structure around the pier shows that the turbulence of the flow around the pier is anisotropic.In the line L4,the transverse turbulence intensity *u and the longitudinal turbulence intensity *v increase gradually from the surface of the water with the increase of the water depth,and then reach the maximum value near the near wall,and then gradually decrease.The reynolds shear stress of different directions varies greatly along the vertical distribution,and its distribution is similar to sinusoidal curve,but the variation range is different.(2)Based on the analysis of the maximum backwater height in the upper reaches of the piers,it is found that the cross-section compensation measures can effectively reduce the maximum backwater height in the upstream and the degree of backwater height is positively correlated with the area of compensation.The influence of the cross section compensation on the flow field at the pier is obvious.After the cross section compensation,the longitudinal flow velocity xV,lateral flow velocityyV and hydrodynamic pressure of the flow near the bridge pier are reduced to different degrees.(3)Regardless of the type of cross-section compensation,the flow capacity of the river section compensation is positively correlated with the area of the cross-section compensation,and increases with the area of the cross-section compensation.The effect of beach slope ratio on the flow capacity is not significant.When the dredging method is used for cross section compensation,if the slope coefficient is 3,the flow capacity Q of the river section compensation is the maximum value.With the increase of dredging width depth ratio,the flow capacity decreases firstly and then increases.