摘要
本文结合国家自然基金项目(50769001)高原湖泊湿地植物-水流-泥沙-污染物交互作用机理研究,选用该项目中两种模型植物(柔性植物和刚性植物)作为研究对象,研究内容主要为柔性植物,刚性植物的生长对梯形明渠水槽水流结构的影响。
本文通过室内水槽试验,研究分析了梯形明渠在无植物覆盖影响下的水流结构,得出了主槽垂线流速最大值发生在主槽中心线处,其最大值点位于水面线下相对水深在0.75-0.85的某点处,而并非在渠道中心自由水面处。选用不同株高的塑料水草来模拟柔性植物,研究分析了在柔性植物影响下的梯形河槽水流特性,得出淹没状态下的河槽垂线流速分布需分为植物冠层上部以及植物冠层下部来分别考虑。通过在模型底部钻孔的方式,选用不同直径的有机玻璃棒来模拟不同生长期的刚性植物,研究分析了刚性植物下的的梯形河槽水流特性,得出主槽流速值大于边坡流速值,断面流速最大值同柔性植物下相同出现在主槽边壁的交界处,横向流速是多个圆柱绕流叠加而成的流速曲线分布。根据本文的试验现象,着重分析了植物覆盖下植物坝中后段边坡水流向主槽汇流的“归槽长度”,定义了本试验中的归槽长度反映的是梯形河槽内主槽及边坡同时覆盖植物下边坡水流开始向主槽汇流至植物坝后达到稳定流态时的长度值。
为了研究梯形河槽植物坝的拦沙固沙机理,本课题在完成清水试验之后针对梯形河槽主槽及边坡覆盖刚性植物的下情况,设计了在河槽内铺设泥沙的植物坝拦沙试验。试验结果得出,植物坝有较好的阻水拦沙作用,有效阻滞了坝前泥沙的起动,使得大部分泥沙在坝内下游段以及坝后段淤积；植物生长对梯形河槽内泥沙的淤积作用是明显的,边坡泥沙在水流、泥沙颗粒、模拟植物的作用下,向主槽输移的现象明显。坝后淤积有明显的“沙波”、“沙纹”出现,在主槽及岸坡的交界处,形成两垄沙丘。
采用数值模拟的方法,应用基于VOF表面跟踪下的RNGκ-ε模型,针对16mm刚性植物覆盖下的在10.31l/s流量时的梯形河槽水流结构进行了模拟计算,计算值与试验值吻合较好。
The paper is supported by the Chinese National Natural Science Foundation (No.50769001),which is the interaction mechanism study on the water flow, sediments, pollutants and plants of the wetland of altiplano lake. The flexible and rigid simulated plants are applied to the research program. This paper especially studies the impact that the flexible and rigid simulated plants exert on flow structure in trapezoidal open flume.
Based on the flume experiment in the lab, this paper emphasizes on the flow structure in trapezoidal open flume without plant covered. The results is that the max velocity of flow lies on the symmetric line of the trapezoidal open flume, the maximum point is in some position of relative water depth's 75% to 85%, not in the free surface of the liquid. Different height green plastic grasses are used as the flexible simulated plants and analyze the flow characteristic of the trapezoidal open flume with the flexible simulated plants. It comes to a conclusion that the flow velocity's vertical distribution is separately researched below the plant canopy and above one with the submerged grasses. By drilling the holes on the bottom of the trapezoidal open flume, choosing synthetic glass sticks in the different diameter as the rigid simulated plants, analyzes the flow characteristic of the trapezoidal open flume with the rigid simulated plants. The conclusion is that the flow of velocity in the major trough is more than in the side slope and the maximum of the sectional velocity lies on the boundary between the major trough and the side slope. The transverse distribution of velocity results from the superposition of flow around many circular cylinders. Additionally, the paper sets forth the definition of the length which is the two sides slope flow of the plant dam converges on the major trough. The definition of the length reflects on the change that is worked by the simulated plants in the trapezoidal open flume.
In order to study the fixing and trapping sediment mechanism with the plant covered in the flume, the experiment of sanding the flume is designed. The results show that the plants dam can not only block water, trap sediment but prevent movement of sand, make the plentiful sand deposits on the downstream position of the vegetable dam. The appearance that the sand from two side slope moves on the boundary is visible. There are two sand ripples and ridges shaped on the boundary.
Based on model of the surface of the tracking VOF RNGκ-εand the numerical simulation of the method was applied, the condition that under the flow of 10.31L/s just for rigid simulated vegetations with diameter of 16mm is computed. The result of computed and experiment is inosculated.
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