小底坡、低Fr数泄洪洞掺气坎体型优化研究

位于小底坡、低佛氏数泄洪洞上的掺气坎,其体型设计往往存在较大难度。为了查明小底坡、低佛氏数泄洪洞掺气坎体型优化设计的一般规律,采用大比尺的模型试验,对三维掺气坎进行了系统研究。小底坡上的掺气坎,可用过坎射流最高点至底板的距离Tmax和空腔回水作为其体型优化的主要目标,良好的掺气坎应使空腔回水最少时Tmax也较小。试验结果表明:Tmax的主要影响因素为平均坎高及掺气坎横断面的型式,平均坎高愈小,Tmax愈小;横断面为凸型的凸型坎,可以减弱出射水流横断面上水面线的凹形分布,能使Tmax相对较小;空腔回水的主要影响因素为平均坎高及坎高差,适当增加平均坎高及横向坎高差,对消除空腔回水有利;在小底坡掺气坎体型优化中,三维掺气坎较二维连续坎有明显的优势,特别是凸型坎,容易达到空腔回水少,同时Tmax也较小的优化目标。

The Optimum Shape of Aerator at the Spillway Tunnel of Slight Slope and Low Fr

Based on a large-scale model experiment,the optimization of the shape of aerator at slight slope of the channel and low Fr spillway tunnel was studied.The result showed that the optimum target of the aerator's sharp can be measured by the minimum amount of invert flow in air chamber and the minimum distance Tmax(between the zenith of the jet and the baseboard).The main factors of Tmax are the average height of aerator and lateral type of the aerator.The more lower the average height is,the more shorter the Tmax is.The convex aerator in lateral direction can weaken the concave distribution of the water surface in lateral direction and decrease Tmax relatively.The main factors of the invert flow in air chamber are the average height and the height difference of areator.Properly increasing the average height and height difference is good for eliminating the invert flow.When optimizing the shape of aerator at slight slope of the channel,the three-dimensional aerator is better than the two dimensional aerator,especially for the convex aerator,which is easy to achieve shorter Tmaxand less invert flow.