Numerical Simulation Study On The Influence Of Spur Dike On The Confluence Area

In order to solve the adverse effects of the confluence of tributaries in the confluence rivers on the navigation of the main embankments and waterways.This paper adopts the method of building a spur dike on the opposite bank of the tributary downstream of the confluence to change the original flow structure of the confluence area to achieve the effect of river governance.Based on the full verification of the physical flume experimental model,a numerical model for studying the influence of the spur dike on the confluence area of the water flow is established based on the three-dimensional k-? turbulence model,the free surface capture technology of the VOF method,and the PISO pressure-velocity coupling algorithm.Using the controlled variable method,study the three cases of different spur dike layout positions,different river width reduction ratios(ratio of spur dike length to main trough width),and different confluence ratios of main tributaries.The influence law of geometric characteristics,turbulent kinetic energy distribution and turbulent dissipation rate distribution of the backflow zone behind the spur dam.The main content and results are as follows:(1)In terms of water level changes.Before the arrangement of the spur dike,after the tributaries merge into the main stream,there will be sloping water at the upstream of the junction,and water falling at the downstream,and the degree of sloping water and falling water will increase with the increase of the confluence ratio.After the spur dike is arranged,there will be spur water on the upstream side of the spur dike,and water fall in the downstream.At the same time,the spur dike will affect the water level on the right bank of the mainstream downstream of the junction.With the increase in the rate of narrowing of the river width,the upper reaches of the spur dam and the lower reaches of the spur dam increase in the degree of water fall.As the confluence ratio increases,the degree of stagnation in the upstream of the spur dike increases,and the degree of downstream drops decreases.(2)In terms of flow velocity distribution.Before the spur dike is arranged,after the tributaries merge into the main stream,there will be areas of larger flow velocity outside the separation zone and on the opposite bank of the tributary.With the increase of the confluence ratio,the area with larger velocity increases and moves to the opposite bank of the tributary and downstream of the main stream.After the spur dike is arranged,the lower flow velocity downstream of the spur dike can play a better role in protecting this side embankment.At the same time,a higher flow velocity appears on the outside of the spur dike head.When the river width narrowing rate is large,it will affect the opposite bank of the spur dike.Stability has an impact.(3)In terms of separation zone and backflow zone behind the dam.Before the arrangement of the spur dike,after the tributaries merge into the main flow,a separation zone will appear downstream of the junction,and the extent of the separation zone will increase with the increase of the confluence ratio.After the spur dike is arranged,on the one hand,a backflow zone will appear downstream of the spur dike,and the size of the recirculation zone will increase with the increase of the narrowing rate of the river width.On the other hand,the spur dike will affect the development of the separation zone on the bank side,and the size of the separation zone at the junction becomes smaller and smaller with the increase of the narrowing rate of the river.(4)The distribution of turbulent kinetic energy.Before the arrangement of the spur dike,after the tributaries merge into the main flow,a larger value of turbulent kinetic energy will appear downstream of the junction,and its range will increase with the increase of the confluence ratio.After the spur dike is arranged,on the one hand,a large value of turbulent kinetic energy will appear downstream of the spur dike,and its range will increase with the increase of the narrowing rate of the river;on the other hand,the area with a large value of turbulent kinetic energy downstream of the intersection on the opposite bank of the spur dike will appear.As the river width narrowing rate increases,the larger range of turbulent kinetic energy in this area decreases.(5)In terms of turbulence dissipation rate.Before the spur dike was arranged,the larger value of turbulent dissipation rate appeared outside the separation zone downstream of the junction,and the larger value range of turbulent dissipation rate increased with the increase of the confluence ratio.After the spur dike is arranged,on the one hand,there will be a large value of turbulence dissipation rate downstream of the spur dike head,and its range will increase with the increase of the river width narrowing rate;On the other hand,it will have an impact on the area with a larger value of the turbulent dissipation rate outside the separation zone downstream of the junction,and the larger value range of the turbulent dissipation rate in this area gradually decreases with the increase of the river width narrowing rate.