台阶式溢洪道滑行水流水面线和消能效果的试验研究

Experimental Research on the Presented Water-Surface Curve of Skimming Flow on Stepped Spillways and Energy Disspation

通过模型试验研究了台阶式溢洪道滑行水流的流态、水面线和消能效果.试验得出,台阶式溢洪道的水流流态分为台阶内部的旋滚流态和虚拟底板以上主流区的流态.台阶式溢洪道水面线的变化与来流量、台阶尺寸和掺气浓度有关.当水流进入台阶段时,水面由于失重有一定的降低,然后逐渐抬高至某一高度后再略有降低;在掺气发生点以前,水面线沿程降低,掺气发生点以后,水面线沿程升高;当水流掺气饱和时,水深沿程不再变化,为明渠均匀流.台阶式溢洪道的消能率是逐级台阶的累积效应.水流通过与台阶之间的碰撞、台阶上的水流漩滚以及水流内部的紊动剪切强化了溢洪道的消能效果.在试验范围内,台阶式溢洪道与光滑溢洪道比较,消能率可以提高40%～70%.通过试验,得出了台阶式溢洪道滑行水流水面线和消能率的计算方法.

The flow pattern the water surface curve and the effect of energy dissipation are investigated via hydraulic model test. There are!two flow patterns on the stepped spillway——internal vortex and main stream zoom on the fictitious bottom. The distribution of water surface curve is related to the discharge, the size of steps and the density of the entrainment air. when the flow enters the steps, the water surface, due to loss of weight, falls to some extent and rises gradually to a certain height and then lowers slightly. The water surface falls before the flow point of air entrainment and then rises afterwards. When the water flow is saturated in air entrainment, the water depth doesn't change to manifest as a uniform flow in open channel. The energy dissipation of water flow is produced by the accumulation of all steps. The effect of the energy dissipation is greatly enhanced owing to the collision of the water with the steps, the water vortex on the steps and turbulent shearing of water. The energy dissipation rate is 40 to 70% higher than that of the skimming spillway. The calculation methods of the water surface curve and the energy dissipation rate are proposed.