三岛型群汊河道平面流场与分流特性研究

Research on Planar Flow Field and Shunt Characteristics of Three-Island Braided River

对三岛型群汊河道平面流场与分流特性的研究是预测污染物混合、富集和分散等水环境保护工作的基础。选取天然河流中三岛型群汊河段,建立三岛型群汊河道水流运动物理模型试验系统,在各汊道布置20个测量断面。详细测量三岛型群汊河道中水流结构参数,得到了7个不同水深处的平面流速分布。基于各测点三维流速与各汊道的流量计算数据,分析表、中、底3层不同水深的平面流场和各汊道分流比的特点。通过绘制分汊岛几何边界的切线,来确定分汊岛附近主流区范围,分析三岛型群汊河道分汊岛布局对分流效果的影响。结果表明:三岛型群汊河道各支汊流量分配存在明显差异,各汊道的分流比例由分汊点位置、分汊岛几何边界位置和汊道平面流速分布共同决定;当分汊点在主流区以内时,分汊点的位置对各汊道分流比例起明显作用。

The study of planar flow field and diversion characteristics of three-island braided river is the basis for predicting water environment protection such as mixing,enrichment and dispersion of pollutants.In this paper,a physical model test system for flow movement of three-island braided river channel is established by selecting braided reach of three-island group in natural river,and 20 measuring sections are arranged in each braided channel.Flow structure parameters in braided channel of three-island group were measured in detail,and plane velocity distributions at 7 different water depths were obtained.Based on the three-dimensional flow velocity at each measuring point and the flow calculation data of each branching channel,the characteristics of the plane flow field at different water depths in the table,middle and bottom layers and the diversion ratio of each branching channel are analyzed.By drawing tangent lines of geometric boundary of braided islands,the range of main flow area near braided islands is determined,and the influence of layout of braided islands of three-island braided rivers on diversion effect is analyzed.The results show that there are obvious differences in flow distribution of branching branches in three-island branching channels.The flow distribution ratio of branching channels is determined by the position of branching points,the position of geometric boundary of branching islands and the distribution of branching plane velocity.When the branching point is within the main flow area,the position of the branching point plays an obvious role in the branching ratio of each branching channel.