Abstract: In water conservancy and hydropower projects , hydraulic tunnel can be divided into diversion tunnel, spillway tunnel, emptying tunnel and water diversion tunnel for power generation, etc. Each of them has a certain flow condition, and it’s easy to control the hydraulic characteristics for a single-purpose tunnel. But when a tunnel has a variety of uses due to technical and economic conditions, the tunnel will be faced with significant hydraulic differences in various operation stages. In this paper, we researched the hydraulic characteristics of slope tunnel which integrates functions of diversion, flood discharge, emptying, and diversion for power generation in different operation stages by hydraulic model test of a water conservancy project. Results reveal that when the tunnel is used as spillway tunnel under normal operation, the flow pattern is normal at the tunnel inlet and in the tunnel, and the minimum pressure in the tunnel meets the requirements of specifications; when it’s used as diversion and emptying tunnel, vertical suction vortex is formed at inlet under certain flow conditions, and air bag whose shape changes and collapses constantly is formed in the tunnel. In long tunnel section and large flow range, mixed free-surface-pressure flow as well as free flow shockwave and deflected flow caused by the bifurcated pipe for power tunnel will also occur. Such flow patterns could induce harmful vibration of tunnel wall and cavitation. Furthermore, through experimental optimization and associated with reasonable dispatch of terminal working gate, the safe operation mode for multipurpose hydraulic tunnel is put forward.

Key words: hydraulic tunnel, bifurcation tunnel, mixed free-surface-pressure flow, flow vortex, hydrodynamic pressure, gate operation