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More and more steep-grade tunnels are applied to the hydroelectricdevelopmentof the mountain rivers. The related research and prototype operation show that the hydraulic characteristics of steep-grade tunnel, such as discharge capacity, flow pattern, flow pressure etc. are different from that of slight-grade tunnel. In the article, based on the model test data of steep-grade tunnels in a lot of hydropower stations, the reasons why there are hydraulic characteristics difference existing between steep-grade tunnel and slight-grade tunnel are analyzed, especially about the influencing factors of free-surface-pressure flow and the related control measures. The research results show the influencing factors offree-surface-pressure flowinclude relative submerge depthH/a, the tunnel shape(bottom slope, inlet top shape, tunnel height, tunnel length, bending section, gate shaft etc.), inlet guiding channel arrangement and the consequent air suction swirl etc. According to the terrain condition, geological condition, project function, operation safety and economic factor etc., some measures can be adopted to improve the mixed free-surface-pressure flow problem in steep-grade tunnels.


Session R19, Hydraulic Applications: Numerical and Experimental Devices and Flow Interaction



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