Numerical investigation on the evolution process of cascade dam-break flood in the downstream earth-rock dam reservoir area based on coupled CFD-DEM

Once a dam-break incident occurs in cascade reservoirs, it may lead to continuous dam-break in downstream cascade reservoirs. Clarifying the evolution law of dam-break flood in the downstream reservoir area is the basis for revealing the peak discharge enhancement mechanisms of cascade dam-break flood, but it has not been extensively studied. In this study, based on the Eulerian-Lagrangian theory, a model coupling computational fluid dynamics (CFD) and discrete element method (DEM) was established, considering the sediment concentration of dam-break flood, and it was verified that the model can accurately simulate the motion law of fluid phase and particle phase in dam-break flood through the benchmarking tests and existing experimental data. It was then applied to simulate the effects of different flood sediment concentration, upstream and downstream water levels, dam-dam spacing, and upstream slope ratio of the earth-rock dam on the evolution process of dam-break flood in the downstream reservoir area. The evolution law of upstream dam-break flood in the downstream reservoir area was revealed from the perspectives of wave climbing height and dam surface pressure. The results showed that compared with not considering the sediment concentration, when the sediment concentration of the dam-break flood was 40%, the maximum climbing height increased by 33.2%, and the peak pressure on the dam surface increased by 41.8%. The main reason was that the increase in sediment particle content improves the viscosity and density of flood. In addition, three typical flood evolution patterns were observed for different upstream and downstream water levels: climbing, leaping, and pushing patterns. In the climbing and leaping patterns, the impact pressure generated by the dam-break flood on the upstream dam heel of the earth-rock dam cannot be ignored. In the pushing pattern, the impact force of the dam-break flood has little effect on the dam surface pressure, but the climbing height at the dam crest increases significantly. The sediment concentration and upstream and downstream water levels were the key factors affecting the evolution law of dam-break flood, while the dam-dam spacing and the upstream slope ratio of the earth-rock dam has little effect.