180°弯曲水槽内床面冲淤演化过程数值模拟

Numerical Modeling of Bed Evolution in 180° Bending Flume

为准确掌握180°弯曲水槽内床面冲淤特征及其演化过程,采用基于非结构化三角形网格的三维流动和地形冲淤数值模型对180°弯曲水槽内床面的冲淤演化过程进行复演。运用标准k-ε紊流模型和显式2步投影方法求解RANS方程,推移质输沙率选取Van Rijn输沙公式计算,对于二次流强度较强、横向坡度对输沙方向影响较大的强弯曲水槽,采用方便实用的Engelund方法计算横向底坡所引起的输沙方向的偏移,同时对河床变形所引起的河床临界起动切应力变化进行修正及对流动和地形冲淤相同时间步模拟非恒定的河床冲淤演化过程。与试验测量结果对比显示:数值模型对强弯曲水槽冲淤特征有较好的模拟效果;Engelund方法对计算输沙方向偏移角度具有明显的改进;模型同样也具备复演内床面非恒定冲淤演化过程的能力。

A three-dimensional numerical model based on unstructured triangle grids was used for predicting the flow and time variation of bed deformation in a 180° channel bend. The standard turbulence closed model and explicit project method were employed to solve the RANS equations. The bed load transport quantity was determined with the Van Rijn formula. For a strong secondary flow and the influence of transverse bed slope on the direction of lateral bed load sediment in sharp channel bend,the simple Engelund model was employed to compute the deviation of the sediment transport. Moreover,the critical bed shear stress of incipient motion was also corrected according to the method advanced by Van Rijn. A full set of unsteady flow and bed deformation process within a same time step was predicted. The predicted bed deformation over time was compared with data from a physical model study and good agreement was found.