Study on Comparison of Energy Dissipation Measures for Retaining Weirs at the Outlet of Large-Scale Low-Lift Pumping Stations

In large-scale low-lift pumping stations, in order to adopt siphon outlet channels under the condition of no water in the outlet channel, a retaining weir needs to be set on the outlet side of the pumping station. To ensure the safe and stable operation of the retaining weir, the problem of energy dissipation of the retaining weir needs to be solved. Based on the VOF two-phase flow model, numerical simulations of three-dimensional turbulent flows were carried out for energy dissipation measures such as stilling basins, toe pier energy dissipation, suspended grid for energy dissipation, and their combinations, and the flow fields, hydraulic characteristics, and energy dissipation effects under different energy dissipation measures were compared. The research shows that the toe pier–suspended grid combined scheme can effectively break and weaken the large-scale vortices behind the retaining weir. Compared with the case of only using a stilling basin for energy dissipation, the maximum bottom velocity is reduced by 31%, and the maximum dissipation rate is increased by 119%. A comprehensive evaluation objective function is established with the relative bottom velocity and energy dissipation rate in the stilling basin as the quantification indexes. Through further analysis, the value of the toe pier–suspended grid combined scheme is the lowest, which is 37.84% lower than that of the traditional stilling basin, and the energy dissipation efficiency is the best. The toe pier–suspended grid combined scheme effectively optimizes flow conditions and improves energy dissipation, offering theoretical and engineering references for the energy dissipation design of retaining weirs in low-lift and large-flow pumping stations.