Hydrodynamic Optimization of Non-Pressurized Tunnel Intersection of Pumped Storage Power Station

The geometry of non-pressurized tunnel intersections governs the hydraulic behavior of the confluence flows, which are critical to the safe operation of pumped storage power stations. To address the issue of water surface levels exceeding the permissible height of the vertical walls at the intersection of the sediment discharge and emptying tunnels close to the lower reservoir of a pumped storage power station, a hydraulic model with a scale of 1:45 was constructed to optimize the intersection design. The optimization process included replacing the straight connection with an arc connection, incorporating an energy dissipation basin into the emptying tunnel, reducing the intersection angle, and increasing the arc radius. During the optimization, the hydraulic behavior of the confluence flow was thoroughly analyzed. This study determined that an arc connection with a 21° intersection angle represented the optimal design. Using the RNG k-ε turbulence model and the volume-of-fluid (VOF) method, a three-dimensional (3D) numerical model was developed to further evaluate the flow patterns, velocity fields, and bottom pressure distributions under both the optimized-design and model-verification conditions. The numerical simulation results, validated against experimental data, exhibited close agreement. The findings demonstrate that the optimized design ensures compliance with specifications, as the maximum water depth no longer exceeds the height of the straight walls. This study offers valuable insights for optimizing tunnel intersections of high-elevation-difference non-pressurized tunnels in pumped storage power stations.