缓坡泄洪放空洞掺气坎水力特性试验分析

Experimental analysis of hydraulic characteristics of aerators in spillway tunnels with mild slope

高速水流掺气是减免流道空蚀破坏的有效措施,然而在缓底坡、大水位变幅条件下,常规掺气坎难以形成稳定无积水的掺气空腔。本文在缓底坡(3.3%)条件下,采用模型试验方法,对比分析了常规连续坎、异型坎及组合坎的水流特性和掺气效果,认为Fr数、掺气坎坡度与水舌落点处底板坡度是影响水流入射角的主要因素;在此底坡条件下,掺气坎尺寸变化的影响要远大于体型变化的影响,采用异型掺气坎亦难有效解决掺气空腔积水问题;经依托工程模型试验论证,组合坎掺气流态良好,适应大变幅的运行水头,可较好地改善缓底坡空腔回流积水问题。

Aeration to high-velocity water flow is an effective measure to reduce cavitation damage.However,under the condition of mild chute bottom slopes and large variations in reservoir stage,a conventional aerator is usually difficult to form stable,water-free aeration cavities.This paper examines the flow characteristics and aeration effects of bottom aerators through model tests under the condition of a mild bottom slope(3.3%),and compares conventional continuous aerators,special-shaped aerators,and combined aerators.We find that three main factors-Fr number,aerator slope,and chute bottom slope at the water nappe landing point-affect the incidence angle of water flow.At the chute bottom slopes tested,the influence of variations in aerator size is much greater than that of shape change;it is difficult to effectively solve the problem of water accumulation in the aeration cavity if a special-shaped aerator is adopted.Based on our scale model tests of a real project,we have shown that the combined sill aerator creates good air flow patterns,and it is applicable to the working heads with large amplitudes and better controlling backflow water in the cavity on mild bottom slopes.