Numerical modeling of flow characteristics and sediment movements in a bend under supercritical flow conditions

Abstract

Sediment bypass tunnels (SBTs) are effective in minimizing reservoir sedimentation by routing sediment-laden flows around the dam under supercritical flow conditions. One of the major challenges in existing SBTs is the wear of the tunnel invert, which intensifies in bends caused by nonuniform sediment concentrations. Recent experimental investigations examined the cause of sediment and abrasion nonuniformity in bends, but for some specific configurations only. Therefore, a computational fluid dynamics – discrete element method (CFD-DEM) model in OpenFOAM was utilized to simulate and validate the flow characteristics and sediment movements in supercritical bend flows, thus helping in improving future SBT designs and maintenance. In this study, the flow and particle motion characteristics are simulated for an existing scale-model of the downstream bend of the Solis SBT. The turbulence was modeled using the renormalization group (RNG) k – ε model. The sediment movements were modeled using an Eulerian-Lagrangian approach with one-way coupling of the fluid-particle interactions and unresolved flow properties around the particles. Additionally, the particle-bed interactions were defined via particle rebound conditions. The CFD simulation results show that although the main core region vortex (MCRV) is captured by the used isotropic turbulence model, the outer wall vortex (OWV) could not be simulated. Interestingly, the concentrated sediment movements toward the inner wall are simulated efficiently and are comparable to previous experimental evidence. These sediment movements are influenced by a component of the MCRV that is acting toward the inner wall. Moreover, using the current computationally economical approach, plausible results can be achieved regarding flow characteristics and particle movements.