The flow patterns of horizontal gyrating discharge tunnel are studied with Gongboxia hydropower station as an example and in combining with wind velocity and pressure graph during the gate opening. The tests systematically describe the flow pattern difference between prototype and models and the variation of flow pattern in weir section, vertical shaft section, starting rotation device, gyrating discharge tunnel , water plunge pool and recession tunnel. The results show that the flow pattern transforms gradually from weir flow to submerged flow in the weir section, and from free drop to submerged jet flow in the vertical shaft section because of the annular aerator and in the process of gate opening. The flow pattern of the gyrating discharge tunnel may be classified into five steps, experiencing the changes from free flow to absorbing flow. The function of the water plunge pool adjusting flow is significant. And the flow in the recession tunnel appears to be the steady open flow pattern.%以公伯峡水电站为例,结合原型风速和压强随闸门开度的变化过程线,研究了水平旋流泄洪洞的水流流态.试验系统描述了堰闸段、竖井段、起旋室、旋流洞、水垫塘及退水洞内水流流态的变化过程,对比分析了原型和模型流态的差异.结果表明受收缩环的影响,在闸门开启过程中堰闸段水流由堰流向淹没流过渡,竖井段水流由自由跌落向淹没射流过渡；旋流洞内流态的变化大致可分为五个阶段,经历由自由流向吸吮流转变的过程；水垫塘调整流态的作用显著,退水洞内水流呈稳定的明流流态.
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