Turbulent Flow in a Central Vertical Slot Fishway: Numerical Assessment with RANS and LES Schemes

Abstract

The application of numerical models for fishway flow enables an improved comprehension of the turbulent flow structure, which is an important covariate used to explain fish passage. Reynolds-averaged Navier–Stokes (RANS) with K-ε closure is the main numerical model to characterize the flow in fishways, but recently, large eddy simulation (LES) has been reported to be better at capturing turbulence in incompressible flows. Comparison between RANS and LES in analyses of fishways flows indicate limitations in both approaches to capture the turbulence parameters or sightly performance of LES for detailed scale studies. Vertical slot fishways are one of the most studied fish ladders, but few studies address the effect of different slot displacements on hydraulic parameters. Thus, the flow of the central vertical slot fishway was simulated in the open-source software OpenFOAM, and two models were applied: (1) RANS with K-ε closure; and (2) LES with the one-equation eddy viscosity (kEqn) scheme. The numerical results were compared to ADV data sampled in a physical model. The flow in a pool of central vertical slots creates two lateral flow recirculation areas and a central straight flux at different discharges and water levels. The RANS K-ε and LES kEqn models provide with the ADV data for all velocity ranges and for the smallest turbulent kinetic energy (TKE <0.03 m2/s2). The LES kEqn model is slightly better in turbulence representation but the RANS K-ε reproduces velocity field more accurately. The RANS and LES model application in fish ladders will be useful for improving the comprehension of fish passage performance and practical aspects of fishways.