基于有限体积法的三维局部冲刷数值模型研究及应用

局部冲刷的三维数值模拟可预测水力冲刷的破坏程度和破坏机制,进而提供更加合理的工程措施以减轻或避免局部冲刷造成的工程破坏。基于有限体积法和非结构化的计算网格构建了以水动力学模型、泥沙冲淤和河床变形方程为基础的三维局部冲刷数值模型。水动力学模型中的湍流模型为剪切应力SST k-ω输运模型,泥沙冲淤以底床切应力大小和分布为基础,水沙模型的耦合采用单向弱耦合方式。首先,通过ANSYS-FLUENT软件数值计算水动力学模型后,将水力特性数据单向传递至泥沙模块,并应用UDF函数二次开发实现泥沙模型的数值计算。利用动网格技术重构因河床地形更新引起的变形网格。与动床圆柱冲刷和丁坝局部冲刷的试验结果进行比较,验证了局部冲刷数值模型的可靠性。从平衡冲深时的冲刷深度和冲坑内水流特性等结果的对比可以看出,该数值模型成功地模拟出最终冲刷地形和形态,并能捕捉不同时刻的三维地形变化。根据数值模型的建立及应用结果分析主要得到以下结论,以切应力观点为基础开发该模型时,具有简易性和较强的可靠性;单元体泥沙通量的重构和床面坡度等因素均影响模型的精度;FLUENT软件提供的动网格技术能较好重构小变形网格,但是重构因地形变化引起的大变形网格时略显不足。

Research and application of three-dimensional numerical model of local scour based on finite volume method

The destruction mechanism and degree of local scour can be predicted by a 3d numerical simulation and then more reasonable engineering prevention measures can be adopted to mitigate or avoid destruction of a structure.In this paper,the 3d numerical model of a local scour including the hydrodynamic model,the equations of sediment erosion and bed deformation were constructed based on the finite volume method and the unstructured grid.The turbulence model in the hydrodynamic model is the shear stress transport SST k-ωmodel.Building of the sediment erosion and deposition equation is based on the size and distribution of the bed shear stress.The coupling of the hydrodynamic and sediment model is one-way coupled.After the hydrodynamic model was calculated by ANSYS-FLUENT software,the hydraulic data including velocity and the shear stress would be transmitted to the equation of sediment erosion and bed deformation.The numerical calculation of the sediment erosion and bed deformation equation was achieved by User Define Function.Deformation mesh created by the updating of riverbed topography was reconstructed by the dynamic mesh technique.The numerical results are compared with the experiment of a local scour around the cylinder by Sumer and the experiment of local scour around the spur dike by Michiue to verify the reliability.The results of the scour depth and the flow characteristics in the scour pit at the moment of scour equilibrium show that the numerical model successfully simulates the final scour topography and morphology,and captures the three-dimensional terrain changes at different moments.The main conclusions were drawn from the analysis of the application of a numerical model.The model developed on the basis of the shear stress has the advantages of simple operation and strong reliability.Besides,the sediment flux reconstruction and bed slope would affect the accuracy of the model.Although the small deformation grids can be better reconstructed by the moving grid technology provided by FLUENT software,the large deformation grids caused by terrain changes would be difficult to reconstruct.