Author(s): Anne-Fleur Lejeune; Damien Calluaud; Gerard Pineau; Laurent David

Linked Author(s): Anne-Fleur Lejeune, Damien Calluaud, Gérard PINEAU, Laurent David

Keywords: Vertical Double Slot Fishway; Ecohydraulics; Turbulent flow; Unsteady flow; Numerical simulations

Abstract: The Water Framework Directive, elected in 2000, require European Union member states to achieve good quality of all water bodies. This aim comes, amongst other things, by insuring the continuity of rivers for fish species, and thus bypass structures were implemented in proximity to obstacles. The use of Vertical Double Slot Fishways (VDSF) has significantly increased over the last ten years, particularly in France (on the 50 existing VDSF, 29 were installed in the 2010s). However, few studies (Fujihara et al., 2003; Huang, 2020) have been conducted on this particular type of fishway since the first testing in 1943, in Canada (Clay, 1995). The proposed study is funded by the French Office of Biodiversity and has two major goals: understanding the turbulent flows inside a VDSF and optimise the design criteria. Unlike the Vertical (single) Slot Fishways (VSF), knowledge on VDFS optimal designs, such as length and width ratios, is scarce. Since the flow is unsteady and three-dimensional, a numerical approach has been chosen to model a specific VDSF, using CFD software Star-CCM+. Fluid dynamics are difficult to predict inside, as it is a cavity flow with high Reynolds number (Re ~ 150,000), combining free surface and two jets mixing together. An experimental 1:6 scale 5 pools fishway prototype, reproducing an existing VDSF in Malause on the Garonne river (France), is simulated. This work follows and makes use of methods previously drawn up in numerical studies on VSF (Ballu et al., 2017). A comparison between three modelling methods has been implemented: RANS (Reynolds-Averaged Navier-Stokes), URANS (Unsteady RANS) and LES (Large Eddy Simulation), with different grid sizes. The goal is to determine the most appropriate method to model the turbulent flow inside a VDSF, and thus to access turbulent and unsteady flow features with accuracy. Hydraulic mean values from all three methods have been assessed, both global values from the middle pool and several specific profiles. The evolution of the flow has been studied with the unsteady simulations: URANS and LES. A grid sensibility study has also been implemented on each of the methods. A future study will focus on reducing the size of the domain of simulation to one or two pools, in order to decrease significantly the calculation time and, if possible, ease the access to turbulent and unsteady features. When both the method and the domain are settled -and after a validation with experimental data, several simulations will be launched to establish the most favourable dimensions for fish to reach upstream, using hydraulics attributes linked to the IPOS parameters (Lacey et al., 2011).

DOI: https://doi.org/10.3850/IAHR-39WC252171192022908

Year: 2022