由泄洪水流引起的水舌风现象的数值模拟分析

The numerical simulation analysis of nappe-wind generated by flood discharge

本文采用细网格非静力能量闭合边界层模式,对水电站大坝泄洪过程中水舌风的生成演变发展过程进行数值模拟。水电站开闸泄洪时,高速水流对气流瞬时的强大冲量作用在坝后形成一个风速较大区,随着高速水流趋向稳定,采用两种模拟方案对水舌风的发展演变过程进行进一步模拟。方案一,通过水气动量交换作用,水流对气流的拖曳力仅来自于大坝溢流面;方案二,拖曳力来自于溢流面及溢流面与消力池接口面。对模拟结果进行分析,发现不考虑水舌风效应时,坝体下风方向出现上下两个方向相反的微弱涡旋;当考虑水舌风作用时,高速水流的瞬时强大冲量作用在坝后形成一个风速较大的逆时针涡旋;水流趋向稳定后,两种方案进行模拟的结果与不考虑水舌风时相比,两个涡旋均得到加强,尤其是处于下面的溢流面处的逆时针涡旋。

A fine-mesh non-hydrostatic energy closure model is employed to simulate the coming and evolving of nappe-wind during flood discharge of hydropower station. A high wind-speed domain is observed behind the dam together with the instantaneous and strong momentum of high-speed liquid-flow on gas-flow when the floodwater of hydropower station is released. Two simulation schemes are applied to simulate the evolving of nappe-wind when the high-speed liquid-flow is stable. An argument is proposed in schemeⅠthat the dragging force of liquid-flow on gas-flow only comes from spillway due to the contribution of air-water momentum transfer. Accordingly, the dragging force comes from spillway and the joint of spillway and stilling basin on schemeⅡ. The results indicate that two weak vortex structures rotating adversely at different height are observed downward from the dam without the effect of nappe-wind. On the other hand, a counterclockwise vortex of high wind speed is found downward from the dam due to the instantaneous and strong momentum of high-speed liquid-flow. The results of both schemes show that the strengthening is found in both of vortex structures in contrast to the ones regardless of the nappe-wind, especially to the lower near the spillway.