Numerical Analysis Of The Flow Characteristics Of A Bifurcated Natural River Channel With A Weir

Braided river is the most common form of natural river,At present,there are many examples of reasonable use of branch water in the application of water retaining structures at the downstream of branch or branch,but the study on the characteristics of natural river flow is not a lot of.Different flow rates,different branch angles of the tributaries and the main stream,the different positions of the weir,the different height of the weir,and the length of the different weirs in the branch will change the characteristics of the river.Near the water from the river often West Branch of water,reasonable arrangement of the West Branch of the water retaining building on the rational use of the West Branch is very important,so the flow characteristics of the numerical calculation and analysis,has important significance on braided river water.In this paper,the shallow water equations,spatial discretization and time integration Mike21 FM software are used to simulate the top section of Dandong love fort,the calculation area is from 2.7km bridge in the east of Dandong to the East Branch of the lower reaches of the 900m,the main stream to the East Branch of the river section of the long,West Branch of the long 1km.And use the result in Dandong model to verify the accuracy of numerical simulation calculation,the model debugging right after increasing boundary condition calculation variables and the branching angle of water flow,influence the flow characteristics of braided channel and weir were calculated and compared.The calculation of natural river flow,different flow different inlet angle and different river weir flow ratio,flow field and the change of the mainstream line.The main conclusions are as follows:(1)Natural river flowWith the increase of the flow rate,the branching ratio of the western branch increases gradually,and the slope becomes smaller and smaller.Along with the increase of flow rate,the recirculation zone in the silted area increases,the effective width decreases,the discharge capacity decreases,more sensitive to cross-strait dike flow.It is also found that the smaller the flow rate of the main stream is the larger,the flow rate of the main line is the more,the water flow pattern is observed in the "straight water,small water sitting curve".(2)Different branching angles of braided channelWith the increase of the branching angle,the branching ratio of the West Branch decreases gradually.Through the analysis of the flow field,it is found that when the branch angle of the channel is less than or equal to 50 degrees,there is little change in the recirculation zone,the recirculation zone decreases linearly when the temperature is greater than 50 degrees.Effect of branching angle on foot on the left bank of the river flow is not obvious,right foot velocity increases with the increase of branching angle.The branching angle of 40 degrees?50 degrees between the two sides of the smaller erosion.(3)The location of the West Branch of different river weirThrough the different locations of the West Branch of Dandong Love River weir weir to analyze the closer to the upstream of the river weir diversion ratio smaller,The shunt ratio between the West Branch X0+400?X0+550 is stable.The width of A and B increases slowly with the increase of width,effective width of cross section decreases,river weir in the upstream more conducive to flood,the velocity of weir crest is relatively large,there will be a sudden drop in flow velocity around 50m.After the water flow through the main stream line weir weir to the left bank of the river,so to strengthen the protection of the left bank of the weir.(4)The height of the West Branch of different weirThere is a linear relationship between the ratio of branch to branch and the elevation of weir crest,according to the requirements of the West Branch,we can use the interpolation method to find the ideal weir height.With the increase of weir,the recirculation zone width is smaller,the effective width is larger,and the left and right bank dike flow the same trend,the elevation of weir did not affect the mainstream line.(5)The length of different weir at the branchThe longer the length of the weir,the greater the diversion ratio of the West Branch,and the lower the flow rate.It has no effect on the width of recirculation zone,and does not affect the effective water width.The left foot with the velocity of weir length increases appear more early,the maximum flow rate appeared at the same point,the maximum value were increased.The length of the weir at the mouth of the branch has a greater influence on the main line at the mouth of the branch,and the longer the length is,the closer the main line is to the central line of the river,the shorter the length and the larger the deviation.