沙波附近紊流拟序结构特性初步研究

Characteristics of turbulent coherent structures over sastrugi in open channels

在底部为定床沙波的循环水槽中采用流场综合分析法将流动显示与计算机图像处理相结合进行系统实验研究 ,重点研究了紊流猝发形态和特性 .分析表明 :沙波床面对明渠紊流拟序结构的特性有重要影响 .水流在沙波坡顶分离 ,沙波周围高于沙波顶部的流区为自由紊流区 ,低于沙波顶部的流区为沙波紊流区 ;在自由紊流区典型的剪切混合层也有显著的以喷射和清扫为主要特征的猝发现象 ;在沙波紊流区的沙波迎水坡面上水流分离 ,在背水坡附近产生漩涡 ;自由紊流区与沙波紊流区之间的紊流拟序结构不同 ,它们相互作用的结果产生了特有的泡漩现象 ;

Based on the synthetic analysis method of flow fields and the combination of flow visualization with computer based image analysis, a series of experimental study is carried out in a circular open flume to simulate dunes and ripples under the variation of flow velocity, with the focus placed on the effects of the bed form of the open flume on the patterns and characteristics of turbulent bursting. It is demonstrated that the bed form of the open flume has significant effects on the characteristics of turbulent coherent structures. Owing to the flow separation at the crest of sand waves, the flow field can be divided into a free turbulent area above the crest and a trough turbulent area below the crest. In the free turbulent area, there are not only shear mixing layers, but also a typical turbulent bursting phenomenon characterized by ejection and sweeping. In the trough turbulent area, the flow may be separated at the upstream slope, and vortexes may occur near the downstream slope. The turbulent coherent structures in the free turbulent area and the trough turbulent area are quite different, and their interaction may result in the so called special Kolk boil phenomenon. The analysis of the experimental results shows that the turbulent coherent structures in the free turbulent area and the trough turbulent area and their interaction play an important role in turbulent flow and sediment movement in alluvial rivers.