Research on Flood Discharge and Energy Dissipation of a Tunnel Group Layout for a Super-High Rockfill Dam in a High-Altitude Region

Abstract

Under the condition of a large dip angle between the flood discharging structure axis and the downstream cushion pool centerline, the downstream flow connection for the discharging tunnel group is poor, and the lower air pressure in high-altitude areas increases its influence on the trajectory distance of the nappe, further increasing the difficulty of predicting the flood discharge and energy dissipation layout. Based on the RM hydropower project with the world’s highest earth-rockfill dam, this paper studies the problem of a large included angle flip energy dissipation layout of a tunnel group flood discharge using the method of the overall hydraulic physical model test. The test results show that the conventional flip outlet mode has a long nappe falling point, a serious shortage of effective energy dissipation space, a large dynamic hydraulic pressure impact peak value on the bottom slab and side wall of the plunge pool, a poor flow connection between the outlet of the plunge pool and the downstream river channel, and a low energy dissipation rate. Considering the influence of a low-pressure environment, when the “transverse diffusion and downward incidence” outflow is adopted, the nappe falling point shrinks by 11 m, the energy dissipation form of the plunge pool is greatly improved, the effective energy dissipation space is increased by 159%, the RMS of the maximum fluctuating pressure is reduced by 74%, the outflow is smoothly connected with the downstream river, the energy dissipation rate is increased by 0.8%, and the protection range of flood discharge atomization is significantly reduced. This effectively solves the safety problems of large included angle discharge return channels and the energy dissipation and erosion prevention of super-high rockfill dams.