植物条件下明渠紊流拟序结构的可视化研究

运用数字图像处理及流动显示技术，对植物条件下明渠紊流拟序结构进行了初步研究。实验结果表明，植物改变了明渠的紊流结构，与无植物条件存在明显差异。根据拟序结构特性，流动可以划分为三个区域：植物内层区，弱猝发现象与类卡门涡街综合作用，尾流涡结构受植物直径及排列方式影响大；植物顶部附近区，紊流结构复杂、结构变化快，同时存在壁面边界层中的猝发现象及自由混合层中大涡配对现象，猝发周期与流速负相关，涡平均渗透深度与流速和淹没度正相关；植物外层区，与明渠外区类似，表现为涡体拉伸及紊流的间歇性。各区紊流拟序结构各不相同，但却相互作用、相互影响。

Flow Visualization Experiments on Coherent Structure in Vegetated Channel Flow

By using the flow visualization technology and digital image processing theory, we studied the turbulent coherent structures in vegetated channel flow. It is demonstrated that the plants in channel has changed the coherent structure which is totally different from that of open channel flows. According to the characteristics of the coherent structure, we divided the flow into three regions. In the vegetation inner region, the wake burst phenomenon and simil-Karman vortex streets coexist and the vortex structure are affected by the dimeter and the arrangement patten of the vegetation. In the region near the top of the vegetaion, the coherent structure is complicated and changes frequently The bursting phenomenon in boundary and large eddy pairing phenomenon in freely mixing layer appeare at the same time in this region, and the bursting period has negetative correlation with velocity, the mean penetration depth of vortex has positive correlation with velocity and submergence. The out region is similar to the free shear turbulence flow which appears in the outer layer of traditional open channel, having the structure can be expressed as vortex stretching and turbulence intermittent. The coherent structures of the three regions are different from but interact on each other.