非对称Y型宽尾墩体型对阶梯掺气空腔长度及负压的影响研究

Study on effects of asymmetrical flaring gate pier Y-shapes on length of aerated cavity and its negative pressure

为了研究Y型非对称宽尾墩体型对阶梯掺气空腔长度和空腔负压的影响,本文采用水气两相流VOF方法的三维RNG k-ε紊流模型,利用几何重建格式进行水气面附近的插值,速度与压力的耦合方式采用PISO算法,用非定常流算法逼近定常流的稳定解,对宽尾墩收缩比分别为0.598、0.497和0.445的Y型非对称宽尾墩＋阶梯溢流坝＋消力池的阶梯掺气空腔长度和阶梯压力分布进行了数值模拟,模拟范围从上游库区至下游消力池尾坎。并对阶梯掺气空腔长度进行实验,将所得实验结果与模拟结果进行对比,发现计算阶梯掺气空腔长度与实测空腔长度基本吻合,最大误差为9.7%。模拟结果显示,随着非对称宽尾墩收缩比减小,阶梯掺气空腔长度逐渐增大,且侧收缩角较大一侧的空腔长度是侧收缩角较小一侧空腔长度的4~5倍。空腔负压随收缩比减小而减少,但阶梯负压分布范围逐渐扩大,各级阶梯外边缘均出现负压,空腔内最大负压出现在首级阶梯垂直固壁面上。

This paper presents a study on the effects of asymmetric flaring gate pier Y-shapes on the length of steps-aerated cavity and its negative pressure. We adopted a RNG turbulence model and a VOF model to simulate the water vapor two-phase flows, and used a PISO velocity-pressure coupling algorithm for iterative solution of geometry reconstruction scheme with the unsteady flow approach. For a stepped spillway with asymmetrical Y-shape flaring gate piers, the study covers a flow domain from the reservoir up to the end sill of downstream stilling basin, and focuses on numerical simulations of the length of cavity and its negative pressure in the conditions of gate piers＇ contraction ratios of 0.598, 0.497 and 0.445. Experimental tests were conducted with the aerated cavity lengths being measured. Comparison of the simulated and measured results shows a good agreement of the cavity length with calculation errors in the range of 9.7%, indicating accuracy and reliability of the present method in successful calculation of cavity length and pressure distribution. The simulations show that as the pier contraction ratio decreases, the cavity length is reduced, and that the length of cavity at the smaller contraction side is four to five times greater than that at the other side. With a decreasing pier contraction ratio, negative pressure on the steps aerated by the air cavity is reduced, but its covering area on the steps expands gradually. At the outer edge of all the steps occurs a negative pressure that takes the lowest value on the vertical face of the first step at the spillway entrance.