Study on energy and momentum correction coefficients in compound open-channel flows

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.