弯道能量耗散及动量输运对床面切应力分布的影响机制研究

弯道床面切应力的合理表达对于弯道水动力过程的准确模拟以及河床冲淤的合理预测至关重要。弯道床面切应力分布的复杂性与弯道环流的存在密切相关，其存在不仅会增大流体质点内部摩擦进而增大弯道水流能量损失，引起弯道床面切应力较顺直河段有所增大，还通过其对动量的输运使床面切应力方向偏离水深平均流速方向。因此，为了阐明并量化弯道环流对床面切应力的影响，本项目拟采用水槽试验、理论分析及数值模拟的方法，围绕弯道环流影响下水流能量耗散引起的床面切应力增大机制，以及动量输运对床面切应力方向的影响机制开展研究。在此基础上构造出弯道床面切应力数值放大因子与方向偏转因子，建立可以反映弯道能量耗散及动量输运影响的床面切应力计算模式。最后将其融入已有的平面二维数学模型，运用该优化后的数学模型计算弯道平面流场，以提高平面二维数学模型模拟弯道平面流场的准确度。研究成果将为进一步预测弯道河床冲淤与平面形态演变奠定基础。

A reasonable expression for bed shear stress in river bends is of great importance to the accurate simulations of the hydrodynamic processes and bed deformation in river bends. The distribution of bed shear stress in river bends is strongly influenced by the secondary flow, which causes the energy dissipation to increase as water flowing through river bends and as a result makes the magnitude of bed shear stress increase. Furthermore, the transport of momentum by secondary flow causes the direction of the bed shear stress to deviate from the direction of the depth-averaged velocity. Therefore, it is important to have a better understanding and more precise quantification of the influences of secondary flow on the bed shear stress. This forms the motivation for this project. Theoretical analysis, numerical simulation and laboratory experiment will be used to study, within the context of secondary flow, the mechanisms underlying the influence of energy dissipation and momentum transport on the bed shear stress in curved channels. The influences of these mechanisms on bed shear stress will be represented by two newly defined parameters, amplification factor and direction correction factor, and then be incorporated in the closure model for bed shear stress accounting for the effects of energy dissipation and momentum transport. Finally, the newly defined closure model for bed shear stress will be incorporated in a two‐dimensional mathematical model in order to perform a more accurate simulation of curved channel flow field. This project will also promote future research on the numerical simulation of bed deformation and planform migration of meandering rivers.