Author(s): Claudia Leuch; Claudia Beck; Ismail Albayrak; Robert M. Boes; David F. Vetsch

Linked Author(s): Ismail Albayrak

Keywords: Vertical bar rack; Curved-bar rack; Downstream fish migration; CFD; Hydropower plant

Abstract: Mechanical behavioural fish guidance structures (FGS) with vertical bars, i.e. louvers and angled bar racks are a promising technical solution for the safe downstream migration of fish at run-of-river hydropower plants (HPP) and water intakes. Such FGS do not pose a physical barrier to most fish but rather create flow patterns that deter fish from passing the bar rack and guide them towards a bypass system. Current knowledge on flow parameters that induce this avoidance behaviour is limited. Furthermore, FGS may impact the energy production and operation of the HPP as they generate additional head losses and affect the turbine admission flow through deflection of the current. In order to provide a widely applicable and robust solution, a balance between good fish guidance and minimal hydraulic losses needs to be found. Computational Fluid Dynamics (CFD) is a valuable tool to efficiently test and compare different FGS geometries such as bar shape, spacing and angle, and rack angle to the flow direction compared to time consuming and expensive physical modelling. Furthermore, the simulation results can be used to investigate the flow field around the bars at high resolution, which can be difficult to obtain in a physical model. Flow patterns near the rack can thus be related to the fish behaviour and the parameters that influence the fish guidance efficiency can be determined. The present study uses a CFD modelling approach to do a parameter study of FGS with different bar shapes, spacings and rack angles. To this end, a CFD model was set up to simulate the near-bar flow field and flow detachment at the bars of the FGSs. Different turbulence models were tested to obtain a model configuration that well reproduces flow detachment and thus hydraulic losses. The model output was validated by comparing the flow fields and the hydraulic head loss coefficients to data obtained from physical model tests of the FGS. The model was subsequently used to analyse the effect of the investigated bar and rack parameters on the hydraulic performance, i.e. the hydraulic losses and the up- and downstream flow fields. The results show that the use of more hydro-dynamically shaped bars significantly improves the hydraulic performance of FGSs. The effect of the approach flow velocity on the flow conditions in the vicinity of the bars is discussed and the results are also evaluated in terms of guidance efficiency of the studied FGS based on the live-fish test results and literature data. The latter is presented in detail in the accompanying paper (Beck et al., 2021). Beck et al. (2021). “Fish Swimming Behavior and Bypass Acceptance at Curved-Bar Rack Bypass Systems”. IAHR 2021, Granada, Spain(submitted)

DOI: https://doi.org/10.3850/IAHR-39WC252171192022442

Year: 2022