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Three-dimensional Numerical Model of Local Scour Based on Finite Volume Method and Its Application

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 作者 单位 E-mail 李登松 四川农业大学水利水电学院 lds809@163.com

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减轻或避免局部冲刷造成的工程破坏。本文基于有限体积法和非结构化数据存储原理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、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Sumer和Michiue等学者关于动床圆柱冲刷、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、冲坑内水流特性等结果的对比后可以看出，该数值模型成功的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、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显的不足。

The destruction mechanism and degree of local scour can predict by the 3d numerical simulation,and then more reasonable engineering prevention measures were adopted to mitigate or avoid the engineering structure destroys.In this paper,the 3d numerical model of local scour including the hydrodynamic model,the equations of sediment erosion and bed deformation was constructed based on the finite volume method and the theory of unstructured data storage. The turbulence model in the hydrodynamic model is the shear stress transport SST k-ω model. The sediment erosion and deposition 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 characteristic data would be transmitted to the equation of sediment erosion and bed deformation.The numerical calculation of these equations is achieved by User Define Function. Deformation mesh caused by the update of riverbed topography was reconstructed by the dynamic mesh technique.The numerical results are compared with the experiment of local scour around the cylinder by Sumer and the experiment of local scour around the spur dike by Michiue to verify the reliability.According to the scour depth and the flow characteristics in the scour pit at the moment of scour equilibrium, the numerical model successfully simulates the final scour topography and morphology, and captures the three-dimensional terrain changes at different moments.According to the building of the numerical model and the analysis of the application results ,the main conclusions were drawn.When the model is developed on the basis of shear stress, it is simple and reliable;Factors such as sediment flux reconstruction and bed slope affect the accuracy of the model.The moving grid technology provided by FLUENT software can better reconstruct small deformation grids, but it is insufficient to reconstruct large deformation grids caused by terrain changes.
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