Computational fluid dynamics in fishway research - a systematic review on upstream fish passage solutions

Computational fluid dynamics (CFD) is increasingly applied in the study of fishways. Applications and methodologies, however, vary substantially among scientific studies and no overview is currently available in the primary literature. Here we review published papers on CFD use in upstream fish passage solutions to identify and describe related spatial-temporal considerations, application fields, scopes and modeling procedures. Vertical slot was the most studied fishway type, followed by nature-like fishways and pool and weir fishways. Most often the CFD model was coupled with physical experiments, but only sometimes associated with actual fish behavior. Reynolds-Averaged Navier-Stokes equations (RANS) was the most frequently adopted set of equations, followed by Large Eddy Simulation (LES), but other promising approaches - scarcely applied so far - were also identified and suggested for future applications - e.g. Detached Eddy Simulation (DES). The use of commercial software was prevalent compared to open-source (notably, Ansys and FLOW-3D). The importance of model validation is highlighted, especially for merely numerical studies, together with the need for three-dimensional CFD to correctly represent turbulent flows. Overall, ecohydraulic studies on the interaction between fish movements and hydrodynamics are needed to complement the CFD-analysis and improve the design of more efficient fish passage solutions.