Abstract: The turning section of tunnel elbow directly impacts the hydraulic characteristics at the side outlet. Improper design of elbow parameters easily causes flow separation within the side outlet. Numerical simulations on the side outlet connected to tunnel elbow were conducted using the RSM turbulent flow model to investigate the effects of parameters such as the radius (R) of curvatureof the elbow, the length (L) of straight tunnel downstream the bend, and the turning angle (α) on outlet hydraulics and also to examine the flow dynamics within the tunnel. Results demonstrate that increasing the radius (R) and length (L) significantly enhances the outlet’s hydraulic performance. Specifically, when R≥12D (where D is the tunnel diameter) and L≥16D, flow separation inside the side outlet diminishes. The flow velocity distribution across the barrier section becomes uniform, eliminating backflow zones. These findings offer valuable insights for designing side inlets/outlets in pumped storage power plants.

Key words: pumped storage power station, side outlet, tunnel elbow, hydraulic characteristics, numerical simulation