A Comparative Assessment of Reynolds Averaged Navier-Stokes and Large-Eddy Simulation Models: Choosing the Best for Pool-Type Fishway Flow Simulations

Fishways are an important solution for mitigating the ecological impacts of river barriers, with their hydrodynamics playing a key role in their effectiveness. Computational fluid dynamics (CFD) is now one of the main tools to predict and characterize flow hydrodynamics, but choosing the most suitable turbulence model is considered one of its main challenges. Although substantial research has been carried out on vertical slot fishways, where the flow is predominantly two-dimensional, studies on pool-type fishways with bottom orifices remain scarce. In this study, three Reynolds averaged Navier-Stokes (RANS) turbulence models (the standard k-epsilon model, the renormalized group k-epsilon (RNG) model, and the standard k-omega model) and the large-eddy simulation (LES) model performances were compared to simulating the flow in a pool-type fishway with bottom orifices. ADV and PIV experimental data were used to assess model performance. While all the turbulence models accurately predicted the discharges and flow depths, the LES model outperformed the others in reproducing flow patterns, velocities, and turbulent kinetic energy. The RNG model also showed reasonable agreement with the experimental data. By contrast, the k-epsilon model delivered the poorest performance, failing to accurately predict the sizes of the recirculation zones and the locations of the recirculation axis and presenting the weakest agreement with the experimental observations. The value of the LES model in studying and characterizing fishway hydrodynamics, particularly concerning turbulence parameters, is highlighted.