裁弯对上下游流态影响的三维数学模型研究

Study on effects of river cutoffs by a 3-D numerical model

裁弯是弯曲型河道演变发展以及河道整治工程中十分常见的现象。裁弯会对上下游河道产生较大影响。本文利用数学模型,采用带旋流修正的紊流模型,同时借助VOF方法描述自由表面,对三个连续畸弯的水流结构进行数值模拟,分析比较了两个裁弯工况对上下游河道的水流结构的影响。计算结果表明:裁弯对上游河道的影响明显大于下游,具体表现为裁弯明显加大了上游垂线平均流速,增大范围与裁弯幅度呈正比,与离开裁弯点的距离呈反比,上游弯道的环流强度同时减弱;裁弯使下游河道纵向流速沿横向分布趋于均匀,影响程度也由裁弯点至下游逐步减弱。

A river cutoff may happen as an event of natural river evolution or the result of an engineering project.It is known that a cutoff will cause a significant change in the river channel both upstream and downstream of the cutoff.In this paper,a three-dimensional numerical model,including the realizable k-ε model for turbulence eddy viscosity and the VOF method for free water surface,is adopted to simulate the complex flows in a model river with successive bends under different cutoff conditions.The results show that a cutoff produces a larger impact on the upstream flow.The depth-averaged velocity there is significantly increased by the cutoff and the variation decreases with the distance from the cutoff.The secondary flow upstream the cutoff has a tendency to be weakened,while the longitudinal velocity downstream the cutoff shows a tendency to become uniform in the transverse direction.