Determining drag coefficients and their application in modelling of turbulent flow with submerged vegetation
Determining drag coefficients and their application in modelling of turbulent flow with submerged vegetation
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DOI：
10.1016/j.advwatres.2014.04.006
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发表时间：
2014-07
影响因子：
4.7
通讯作者：
Hongwu Tang;Zhijun Tian;Jing Yan;Saiyu Yuan
中科院分区：
文献类型：
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作者：
Hongwu Tang;Zhijun Tian;Jing Yan;Saiyu Yuan
植被是自然河流、洪泛区和灌溉渠道中水资源和生态的一个关键方面。当有沉水植物存在时，水流的水力阻力发生了很大的变化。三种阻力系数，即，孤立圆柱体的阻力系数、圆柱体阵列的整体阻力系数以及垂直分布或局部阻力系数通常用作表示植被阻力的参数。本文介绍了明渠水流中淹没茎的综合试验研究。根据我们的实验结果和以前的研究数据，获得了三个阻力系数的经验公式。采用两层模型求解平均动量方程，计算各阻力系数下的垂向平均流速分布。通过比较速度分布模型的预测值和测量结果，我们发现，模型的阻力系数为一个孤立的圆柱和局部阻力系数是很好的拟合。此外，与体积阻力系数的模型给出了更大的速度值比测量，但它可以通过添加床摩擦的影响，并选择冠层内的深度平均速度得到改善。
Vegetation is a key aspect of water resources and ecology in natural rivers, floodplains and irrigation channels. The hydraulic resistance of the water flow is greatly changed when submerged vegetation is present. Three kinds of drag coefficients, i.e., the drag coefficient for an isolated cylinder, the bulk drag coefficient of an array of cylinders and the vertically distributed or local drag coefficient, have been commonly used as parameters to represent the vegetation drag force. In this paper, a comprehensive experimental study of submerged stems in an open channel flow is presented. Empirical formulae for the three drag coefficients were obtained based on our experimental results and on data from previous studies. A two-layer model was developed to solve the mean momentum equation, which was used to evaluate the vertical mean velocity profile with each of the drag coefficients. By comparing the velocity distribution model predictions and the measurement results, we found that the model with the drag coefficient for an isolated cylinder and the local drag coefficient was good fit. In addition, the model with the bulk drag coefficient gave much larger velocity values than measurements, but it could be improved by adding the bed friction effect and making choice of the depth-averaged velocity within the canopy layer.