不同挑坎下首级台阶角度对阶梯溢流坝面掺气影响研究

Study on the effect of first stage angle on the aeration of stepped spillway under different pre-aerator angels

前置掺气坎与首级阶梯对阶梯溢流坝的掺气消能有着重要的影响作用,该文以水工模型试验为依托,结合某水电站,确定模型几何比尺为Lr=60。通过对Y型宽尾墩+阶梯溢流坝+消力池的联合消能工过渡阶梯上首级台阶台面上挑5°、10°及15°和前置掺气坎角度取8°和10°,共六种组合方案分别进行了水工模型试验。并从空腔长度、掺气浓度、台阶负压、底板时均压力和消能率等各个方面,寻找能改善掺气特性的过渡台阶衔接体型。结果表明:随着前置掺气坎角度增大,首级台面角增加不超过10°时,阶梯溢流坝面上底空腔长度和掺气浓度逐渐增大,负压减小,可有效保护阶梯,防止空蚀破坏。且流速减小,压强增大,消能率也随之略有增长,更利于对下游的保护作用。故前置掺气坎为10°,首级台阶台面角为10°时即方案五为最优组合方案。

The pre-aerator and the first step have an important effect on the aeration of stepped spillway. In this paper, based on the hydraulic model test, combined with a hydropower station, the geometric scale of the model Lr = 60 is determined. Three types of the table-board angle of first step respectively up 5 °, 10 °, 15 ° and two pre-aerator angels of 8 °, 10 ° are considered. A total of six combined conditions are set on the Y-shape flaring gate piers combined with stepped spillway and stilling basin withhydraulic model test, to find the optimal level of table size improving the aerosol characteristics by the cavity length, aeration concentration, step negative pressure, time-averaged pressure on stilling bottom, energy dissipation ratios and other aspects. The results show that the lengths of the bottom cavity and the concentration of the aerosol gradually increase with the increase of the pre-aerator angels, and when the increase of the first table angle does not exceed 10 °. This can effectively protect the ladder to prevent cavitation damage. When the flow rate decreases and the pressure increases, the energy dissipation rate also increases. It is more conducive to the protection of the downstream. So the fifth group of programs about the pre-aerator angel of 10 ° and the first stage table angle of 10 ° is the best combination.