分期导流围堰束窄河床二维水流特性模拟及分析

Numerical simulation of two-dimensional characteristics of flow narrowed by cofferdam in phased diversion

围堰束窄河床水流是水利水电工程建设过程中经常遇到的一种流动现象。束窄河床的水流条件不仅与围堰坡脚冲刷与护固关系密切,而且还会影响施工期围堰河床的行洪和通航,因此束窄河床水流条件的变化和影响历来是施工部门关注的重点。本文以分期导流围堰束窄河床水流为研究对象,采用控制体积法建立平面二维水流数学模型对其运动进行模拟。根据试验观测的水面线和断面流速分布资料,对数学模型进行验证。在此基础上,根据数值模拟结果分析比较了4种束窄度下围堰附近的水流运动特性,结果表明,围堰束窄度越大,其上游的壅水程度、进口附近的水流跌落、束窄段水流流速以及下游回流范围也越大,下游水深恢复到不受围堰影响的位置也越靠近下游,但束窄段水流却随着束窄度不同呈现出不同变化。

At the construction stage of hydraulic work on a river, a cofferdam of phased diversion narrows the riverbed and causes a change in the flow around it. This change depends on the toe scouring and reinforcing of the cofferdam and causes certain effects on the flood discharging capacity, navigation conditions and deformation of the river. This paper presents simulations of flow in the reach of riverbed narrowed by a phased- diversion cofferdam, using a depth-integrated 2-D numerical model based on solution by finite-volume method. This model was validated by experimental data of velocity and water stage, and the analysis in this paper focuses on four different ratios of flow contraction around the cofferdam. It is found that the cofferdam might significantly affect the flow field and that the contraction ratio was one of the major factors. A greater contraction ratio results in deeper and farther backwater and greater water surface drop at the entrance of narrowed section, with higher flow velocities in this section and a lengthened recirculation zone downstream. When different shapes of flow contraction are adopted, however, different trends appear in the variations of flow around the narrowed section.