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Study on energy and momentum correction coefficients in compound open-channel flows
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摘要: 在复式断面明渠流中，能量及动量校正系数对水力学计算结果的精确性有直接影响。为研究水深比（滩地水深与主槽水深之比）及滩地植被密度对复式断面明渠流能量及动量校正系数的影响，采用基于壁面建模的大涡模拟（WMLES）方法的三维数值模型，对5种水深比和3种植被密度工况进行数值模拟研究。结果表明：由于流速分布不均匀，主槽和滩地的能量及动量校正系数有明显差异，其值均大于1。随着水深比的增大，复式断面的流速分布趋向均匀，能量和动量校正系数随之减小，能量校正系数的变化范围为1.07~1.19，动量校正系数的变化范围为1.03~1.07。此外，随着滩地植被密度的增大，滩地与主槽的流速差值变大，能量和动量校正系数随之增大，能量校正系数的变化范围为1.09~1.59，动量校正系数的变化范围为1.04~1.21。最后，通过回归分析发现能量校正系数与动量校正系数存在线性关系，所得计算式可用于相同工况条件下能量及动量校正系数的预测。Abstract: In compound open-channel, the energy and momentum correction coefficients have a direct impact on the accuracy of hydraulics calculation. The purpose of this study was to investigate the impacts of flow depth ratios and vegetation densitis on the distributions of energy and momentum correction coefficients in compound open-channel flows. Numerical simulations were performed with a three-dimensional model with the wall-modelled large eddy simulation (WMLES) method for five depth ratios conditions and three vegetation densities conditions. The results show that the correction coefficients of energy and momentum between the main channel and the floodplain are obviously different due to the non-unifomity of velocity distribution. The values are all greater than one. When the flow depth ratio increases, the velocity distribution of the compound section tends to be uniform. The range of the energy correction coefficient and momentum correction coefficient are 1.07~1.19 and 1.03~1.07, respectively. In addition, with the increase of vegetation density, the velocity difference between the main channel and the floodplain increases, and the correction coefficients of energy and momentum of the section increase accordingly. The range of the energy correction coefficient and momentum correction coefficient are 1.09~1.59 and 1.04~1.21, respectively. Finally, through regression analysis, it is found that there is a linear relationship between energy correction coefficient and momentum correction coefficient, and this formula can predict the value of energy correction coefficient and momentum correction coefficient under the same condition.
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图 3 不同水深比下复式断面能量和动量校正系数分布
Figure 3. Distribution of correction coefficients of energy and momentum in compound sections with different flow depth ratios
图 4 能量及动量校正系数随水深比的变化
Figure 4. Values of the kinetic energy and momentum coefficients against different flow depth ratios
图 6 不同植被密度下复式断面能量和动量校正系数分布
Figure 6. Distribution of correction coefficients of energy and momentum in compound sections with different densities of vegetation
图 7 能量及动量校正系数随植被密度的变化
Figure 7. Values of the kinetic energy and momentum coefficients against different densities of vegetation
表 1 计算工况
Table 1. Computation conditions
工况 滩槽水深比 水深 植被密度阻力系数 /m−1 雷诺数 弗劳德数 网格数量 主槽/m 滩地/m 主槽 滩地 1 0.10 0.08 0.008 0 0 31 653 0.76 160×100×80 160×100×10 2 0.17 0.08 0.013 6 0 43 843 0.76 160×100×80 160×100×15 3 0.25 0.08 0.020 0 0 47 779 0.65 160×100×80 160×100×20 4 0.50 0.08 0.040 0 0 67 189 0.56 160×100×80 160×100×40 5 0.75 0.08 0.060 0 0 79 793 0.48 160×100×80 160×100×60 6 0.50 0.08 0.040 0 0.28 67 112 0.56 160×100×80 160×100×40 7 0.50 0.08 0.040 0 1.13 67 112 0.56 160×100×80 160×100×40 8 0.50 0.08 0.040 0 2.26 67 112 0.56 160×100×80 160×100×40 
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