弱混合条件下支流入汇口水力特性数值模拟

Numerical Simulation of Hydraulic Characteristics of Tributary Confluence under Weak Mixing Conditions

库区河道中支流来流较小时,水体和污染物受到干流的阻碍作用滞留在支流入汇口,严重时易在支流暴发水华。采用数值模拟结合水槽实验的方法,研究了弱混合条件下支流入汇口的水力特性。采用RNG k-ε紊流模型封闭水流控制方程,建立了明渠交汇水流三维数值仿真模型,模拟所得垂向流速分布及流场矢量图等结果与水槽试验数据吻合程度较高。基于4种汇流比和3种交汇角工况的数值模拟结果,提出了弱混合条件下支流入汇口水流结构分区,分析了不同交汇条件对入汇口关键水力特性的影响。研究发现:弱混合条件下支流入汇口右岸产生回流形成回水区,左岸水体受到挤压形成加速区,回流流速峰值出现在近右岸壁面处;不同交汇角条件下回水区长度大小为:150°>30°>90°,回水区长度随着汇流比增加而逐渐减小直至回水区消失;回水区最大宽度处距交汇区距离与汇流比成反比;入汇口紊动能峰值区域面积和峰值大小与汇流比成反比,与交汇角成正比,交汇角对紊动能的影响较汇流比更大。

When the tributary discharge in the reservoir channel is small,the water and pollutants from the tributary are retained in the tributary confluence due to the obstructing effect of the main stream,and in serious cases,it is easy to burst large areas of algal bloom in tributaries.In this paper,the hydraulic characteristics of tributary confluence under weak mixing conditions are investigated by using numerical simulations combined with flume experiments.The RNG k-εturbulent model is used to close the control equations,and a three-dimensional numerical simulation model of the open channel intersection flow is established,and the simulation results such as vertical flow velocity distribution and velocity vector diagram are in great agreement with the open channel flume experiments data.Based on the numerical simulation results of 4 different convergence ratios and 3 different junction angles conditions,the flow structure partitioning of the tributary confluence under weak mixing conditions is proposed,and the effects of different junction angles and convergence ratios on the key hydraulic characteristics of the tributary confluence are analyzed.The study found that,under the weak mixing conditions,the right bank of the tributary confluence generates backflow to form a backwater zone,and the water of the left bank is squeezed to form an acceleration zone,and the peak backflow velocity occurs near the right bank wall;the length of the backwater zone under different junction angle conditions is 150°>30°>90°,and the length of the backwater zone gradually decreases with the increase in the convergence ratio until the backwater zone disappears;and the distance between the maximum width of the backwater zone and the confluence is inversely proportional to the convergence ratio;both the high turbulent kinetic energy region size and value at the tributary confluence are inversely proportional to the convergence ratio and positively proportional to the junction angle,and the influence of the junction angle on the turbulent kinetic energy is greater than that of the convergence ratio.