泄洪隧洞急流弯道水力特性

Hydraulic characteristics of supercritical flow along a tunnel bend

由于泄洪隧洞明流弯道流速大、弗劳德数高、流态复杂,因此极少在工程中应用,相关水力特性研究也较少。本文采用物理模型试验方法,对城门型泄洪洞急流弯道及其下游水流进行了观测。试验结果表明:弯道内水流具有轴向前行与由凸岸流向凹岸的横向运动,由此产生凸岸水面逐渐降低、凹岸水面逐渐爬高的发展趋势;凹岸水流超过隧洞直墙的部分紧贴洞顶继续沿轴向前行,同时其横向运动方向演变为由凹岸指向凸岸;洞顶贴壁水流跃过洞顶最高点后,沿着凸岸直墙下滑,形成瀑布;水流在弯道内呈现出环状状态,在下游平直隧洞内逐渐演变为表面起伏波动的水流。根据试验结果,建立了凹岸水流冲击拱顶初始位置及第一波峰冲击拱顶范围的预测经验公式,为泄洪隧洞弯道段设计提供参考。

Supercritical flow in a tunnel bend possesses the characteristic of high velocity,large froude number and complex flow pattern,so this tunnel bend is rarely used in practice and studies on the hydraulic characteristics are few.The flow in the bend and the downstream straight reach were observed in a physical model.The flow moves ahead both in the tangential and transverse directions from the inner to the outer wall.The surface along the inner wall drops while the other one climbs.The flow along the outer wall exceeding the vertical wall clings to the arch.The direction of the transverse motion become from the outer wall to the other.The wall-attached flow slip down the inner wall as it passes the apex,forming a waterfall.The hollow swirling flow pro-duced in the bend develop into a shock wave with a fluctuating surface in the straight tunnel.Empirical formulas were established for predicting the inception location where the flow impinges on the top as well as the impingement range.The findings may be helpful in the design of tunnel bend.