交汇角对明渠交汇口污染物输运特性影响的数值模拟分析

针对等宽矩形断面明渠交汇口建立三维两相流水动力-污染物耦合数学模型，将污染物视作保守物质，不考虑其降解作用。该耦合模型以雷诺应力模型为基础，定量研究不同交汇角工况下交汇口的分离区几何特性及污染物输运规律。计算结果表明：交汇口分离区几何形状、污染物分布特性均存在明显的三维特征，且受交汇角影响；交汇角较大时分离区的几何对称性更强，不同交汇角下断面环流的位置不同，污染物的分布也不同，污染带最大宽度、混合界面宽度均随交汇角的增大而增大；分离区及其上游污染物混合速率随交汇角的增大而加快，在流速恢复区及其下游，混合速率基本不受交汇角影响，其沿程变化符合指数函数关系。

Numerical simulation and analysis of pollutant transport at an open channel confluence under different junction angles

A three-dimensional (3D) two-phase hydrodynamic-pollutant-coupled mathematical model for an open channel confluence of rectangular cross section with equal width was established. The pollutant was considered conservative and the degradation effect was not taken into account.Based on the Reynolds stress model, the geometric characteristics of separation zone and the pollutant transport laws under different junction angles were quantitatively analyzed. The calculation results show that the geometry of the separation zone and pollutant distribution at the confluence have obvious 3D characteristics and are affected by the junction angles. The geometric symmetry of the separation zone is stronger when junction angle is larger. The pollutant distribution is different because of different locations of the secondary flow under different junction angles. The maximum width of the pollution zone and the width of the mixing interface increase with the junction angle.The mixing rate of pollutants upstream of the separation zone increases with junction angles.Downstream of the velocity recovery zone, the mixing rate is not affected by the junction angles, which has an exponential relation with the downstream distance.