Three Dimensional Numerical Simulation Of Flow And Sediment Movement In Double Curved Channel Under The Influence Of Piers

Due to the special boundary conditions,the flow structure of curved channel presents irregular three-dimensional characteristics,the law of water and sediment transport and the evolution characteristics of riverbed erosion and deposition are complex and changeable.With the development of social economy,more and more urban planning is building all kinds of bridges in curved rivers to build urban high-speed traffic network.The existing research on the flow and sediment characteristics of bends is mainly focused on a single simple bend.Many natural bends in nature are composed of many bends,and there are many hydraulic structures such as piers on the bends,which makes the flow characteristics of bends obtained in a single bend have great limitations.Therefore,it is particularly important to study the threedimensional flow and sediment characteristics of double bend under the influence of piers.In this paper,the volume model of water gas two-phase flow(VOF)and the Eulerian model of water sand two-phase flow(Euler)are used,and the Realizable k-? model,which has advantages in swirling flow and secondary flow simulation,is applied-? Turbulence model is used to simulate the flow and sediment transport in the double bend.The influence of piers on the flow and sediment transport in the double bend is studied by comparing and analyzing the transverse gradient of water surface,longitudinal velocity,transverse velocity,hydrodynamic axis distribution and sediment transport law in the continuous bend with and without piers.From the analysis of the simulation results,we can get the following conclusions:(1)In the double bend open channel flow,the backward bend flow and forward bend flow will influence each other.The development of backward bend circulation structure in continuous bend is restrained by the circulation structure in the opposite direction of forward bend.The forward bend circulation structure still plays a great role in the backward bend section,and the center of circulation structure moves up,which makes the flow and sediment movement law in continuous bend different from that in single bend.(2)Under the superposition of pier and bend,the water surface transverse gradient at the downstream of the pier is obviously strengthened,but it is opposite in the adjacent area of the pier.Because of the water blocking effect of the pier,the influence of the pier and the bend are partly offset,and the water surface transverse gradient is only 1/2 of that without pier;The center of high velocity can move down 1.2 m to the bottom of the channel,which can aggravate the erosion of the convex bank;At the same time,the bridge pier divides the circulation through the whole section into three small circulations with the same direction.After leaving the bridge pier,the circulation structure has a process of accelerating development,and the center of the circulation structure in the bend tends to shift to the convex bank.(3)After the construction of bridge piers,the scouring degree of forward bend of double bend is intensified,and the maximum transverse scouring width can reach 0.2 times of the river width,but it has a restraining effect on the transverse sediment transport capacity of backward bend.The scouring degree of the three schemes of building bridge piers on the concave side of backward bend of double bend is much smaller than that without bridge piers,which is only 1/ 2 of that without bridge piers.Among the three schemes of building piers,scheme 3 has a greater impact on the hydraulic characteristics and sediment erosion and deposition of the double bend,and has the widest impact range.Therefore,this scheme should be avoided as far as possible when building piers.In view of the problems caused by the construction of bridge piers,such as the increase of water surface transverse gradient,the enhancement of circulating current intensity and the increase of forward bend scouring intensity of continuous bend,the bank protection of forward bend concave bank should be strengthened after the construction of bridge piers,and the river channel should be excavated on the convex bank side to regulate the river,so as to reduce the water surface transverse gradient,weaken the circulating current intensity and adjust the crosssection velocity,So as to improve the river surface morphology and navigation conditions.In general,this study carried out a multi-dimensional and multi factor system analysis on the characteristics of water and sediment transport in double bend channel through threedimensional mathematical model,enriched and developed the theory of water and sediment transport in bend channel,and provided a scientific decision-making basis for the construction of hydraulic structures in bend channel.