The research on the internal flow pattern characteristics of steep slope tunnel

More and more steep-grade tunnels are applied to the hydroelectric development of the mountain rivers. The related research and prototype operation show that the hydraulic characteristics of steep slope tunnel, such as discharge capacity, flow pattern, flow pressure etc. are different from that of slight slope tunnel. In the article, based on the model test data of steep slope tunnels in a lot of hydropower stations, the reasons why there are hydraulic characteristics difference existing between steep slope tunnel and slight slope tunnel are analyzed, especially about the influencing factors of alternation of free and pressure flow and the related control measures. The research results show the influencing factors include relative submerge depth H/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 alternation of free and pressure flow problems in steep slope tunnels.