Abstract: Baffle-drop shaft is an effective energy dissipation structure in urban deep tunnel drainage system. Different structural parameters of the shaft result in large differences in flow capacity and energy dissipation rate. Through experimental study and numerical simulation (using realizable k-ε turbulence model and volume of fluid(VOF) method), the flow pattern, the maximum flow capacity, the outlet flow velocity and the energy dissipation rate of the shaft with different baffle spacings and baffle angles are analyzed. Results demonstrate that the basic flow patterns in the baffle-drop shaft can be summarized into three categories: wall-limited flow, critical flow, and free-fall flow. Increasing the baffle angle is conducive to the transition of flow pattern from wall-limited flow to free-fall flow. Therefore, a proper baffle angle is critical to the design of the shaft. The maximum discharge of the shaft increases as the baffle spacing and baffle angle increase. The energy dissipation rate of the shaft declines with the increase of inflow. Considering both maximum flow capacity and energy dissipation, the shaft performs the best when shaft diameter is 10 m with a baffle spacing of 4.85 m and baffle angles from 9° to 11°. The research finding offers technical support for the design of deep tunnel drainage systems.

Key words: baffle-drop shaft, model test, numerical simulation, optimization of structural parameters, deep tunnel drainage system