Study On The Variation Law Of The Polluted Mixed Zone In The Bend River

All the rivers in nature are winding,can be regarded as a combination of straight river and bend river.In order to understand the distribution of pollutant emission concentration and the characteristics of pollution mixing zone of the river in nature,that needs to deepen research on the winding river and straight river.At present the relevant research on the straight river is quite mature at home and abroad,obtaining many important results.But the relevant research on the bend river is almost blank.In order to understand the distribution of pollutant emission concentration and the characteristics of pollution mixing zone of the winding river,the water flow and water quality of the bend river with different bending angles and center radius were simulated by the two dimensional hydrodynamic model(RMA2)and water quality model(RMA4)of surface water model system(SMS)in the passage,The flow characteristics of the bend river are described with the simulated data,The change rule of flow field and concentration field in bend reach is also discussed,Then,a simplified algorithm is presented for the geometric parameters(length,maximum width and area)of the pollution mixing zone in the bend river.Finally,it discusses the relationship between the location of discharge port,the flow and water depth of the river and the geometric parameters of the mixed zone.The specific research methods and conclusions are as follows:1、Taking the U type bend as an example,the basic characteristics of bend flow are discussed,It is concluded that the water level changes after entering the bend,In the horizontal,concave bank is high and convex bank is low,From concave to convex showed a decreasing trend;In the longitudinal direction,entrance is high and exit is low,from the entrance to the exit is also showing a trend of decrease;but the curve of the concave bank is convex,the curve of the convex bank is concave,the surface of the whole bend presents a distorted surface.the Longitudinal velocity of the concave bank of bend river at the entrance along the way decreases first,increased slowly after entering the curve,the trend of change suddenly in a rapid increase in the outlet,and then reduce;in the convex bank the change rule is contrary to the concave bank.In the horizontal,convex bank is high andconcave bank is low,from concave to convex constantly increased.Because of the centrifugal force,lead to the two-dimensional flow in bend deviation from the concave in a certain,the velocity component that pointing to a river of the flow is perpendicular to the concave.2、Through a series of simulation and calculation of different bend radius and bend angle with concave bank and convex bank of the bend river.We conclude the change rule of flow field and concentration field with blow down circumstance,analyzing the reason of change rule.We find that the flow rate of the bend river is decline with the increasing of different bend radius and bend angle.The change rule of the water depth and flow pipe flow of both bank.The concave bank shore flow pipe flow declines as the increasing of the bend radius.But on the contrary of the convex bank.At the same time we focus on the study of the exceed concentration field(pollution mixing zone),Analyzing the bend Angle,the bend radius and relatively higher allowable concentration values influenced on the geometrical characteristic parameters of pollution mixing zone.The result is that the decline of geometric characteristic parameters of pollutant mixing zone with the increasing of the bend angle,the increase value of allowed relative concentration.But the increasing of the geometric characteristic parameters with the decline of bend radius in the pollutant mixing zone of the concave bank.But in the contrary of the convex bank.Comparing the pollution mixing zone of the concave bank 、 convex bank and straight section.We find that curved reach pollution mixing zone geometric feature parameters in less than straight section,and in the concave bank is less than the convex bank in the bend of the river usually。3、Based on the constitutive relation of the geometric characteristic parameter of the polluted mixed zone in the straight river,through the dimensional analysis and curve fitting to modify the theoretical solution of the straight reach,a simplified calculation formula for the geometric characteristic parameters of the polluted mixed area in the curved reach is obtained.The error analysis of the results obtained from the simulation and the results obtained by the formula,obtained satisfactory results.4、Finally,taking the U type bend as an example,the influence of the location of sewage outfall,the flow of the river and the water depth on the polluted mixing zone were researched.Analysis of the influence of the location of sewage outfall,obtain that when the location of sewage outfall at the beginning and end point of the both sides of the bend,the geometric characteristic parameters of the polluted mixed zone are relatively large.The other location in the bending river is relatively small,and in the concave bank with the change of the location of sewage outfall from the entrance to the exit,the geometric characteristic parameter of the location of sewage outfall is slowly reduced;in the convex bank with the change of the location of sewage outfall from the entrance to the vertex,the geometric characteristic parameter of polluted mixed zone increases slowly,after the vertex is slowly reduced.Analyzed the influence of the river flow obtain that when the water depth is constant,the geometric parameters of the polluted mixed zone decreases with the increase of the flow.Analyzed the influence of the depth of water obtain that when the the river flow is constant,the length and area of polluted mixed zone decreases with the increase of the depth,and the maximum width of the polluted mixed zone does not change with the change of water depth.