Hydraulic Coupling-Induced Flow-Regime Transition and Energy Dissipation Characteristics in Cascade Flood Discharge Systems of Large Tailings Storage Facilities

Hydraulic analysis of complex flood-drainage systems is critical for the safety design of large tailings storage facilities. Conventional approaches are limited in their ability to precisely characterize three-dimensional flow fields and flow-regime transition processes under multi-structure coupling conditions. A three-dimensional FLOW-3D model was developed for the Diyan tailings storage facility using the RNG k-ε turbulence model and Tru-VOF method. The system comprises three internal drainage shafts, three external overflow shafts, and more than 4 km of connecting tunnels. Simulated discharges exceeded the corresponding design values by 2.3–26.5%. All internal drainage tunnels remained under free-surface flow. The available CFD cases bracketed the free-surface–pressurized transition of the coupled No. 1 and No. 2 overflow shafts between upstream heads of 1.0 and 2.0 m. Downstream hydraulic control propagated backwater through the connecting tunnels, altered the upstream flow regime, and reduced the rate of discharge increase. Total-head dissipation ratios ranged from 58.2% to 99.7%. Within the internal drainage system, larger vertical drops were generally associated with lower residual outlet velocities and higher dissipation ratios. The results provide an engineering-scale numerical assessment of hydraulic interaction, backwater propagation, and flow-regime change in a cascade flood discharge systemfor the hydraulic evaluation of similar configurations.