A novel approach for simulating self-propelled swimming fish: Implications for injury risk at pump and turbine intakes

Overview & Synopsis

Assessing fish injury and mortality risk in pumping and hydropower systems is increasingly important as operators work to meet ecological performance goals and comply with environmental legislation requiring safe fish passage. While risks of fish injury associated with hydraulic pumps and turbines are better documented, the risks that fish experience in closed-conduit passages, such as pump and turbine intakes, pipe-based fishways, and aquaculture transfer pipelines, remain understudied, limiting the ability to evaluate and improve system design. This study introduces a novel Computational Fluid Dynamics (CFD) approach to quantify how hydraulic conditions common to pump and turbine intakes and fish reaction interact to influence injury risks in such flows. Using brown trout (Salmo trutta) as a representative species, fish trajectories and reactions are modelled with three-dimensional CFD employing a Dynamic Fluid-Body Interaction, which allows for a free body motion in space by solving the fully coupled six-degree-of-freedom (6-DOF) equations of motion. In addition, the method incorporates mesh morphing techniques to reproduce realistic undulatory or oscillatory swimming, with movement transitions activated by predefined trigger points. The predicted trajectories of self-propelled fish were consistent with live-fish experiments with juvenile silver perch (Bidyanus bidyanus) travelling through pipe components. Simulations conducted for three common closed-conduit components, namely, a 90-degree bend, an expansion, and a contraction, show that fish moved safely through each configuration, with no harmful collisions. Hydrodynamic exposure levels for pressure change, shear strain rate, acceleration, and shear stress remain within accepted biological thresholds. The proposed methodology enables fish movements through conduits to be simulated. It therefore has the potential to become an important tool for ethohydraulic experiments on fish. At the same time, it allows for a comparative assessment of potential injury mechanisms when fish pass through various hydraulic structures, such as pumps and turbines, and provides a detailed picture of fish-fluid interactions. It therefore contributes to a broader evidence base that can be used by operators and researchers to consider injury risks to fish when passing through hydraulic structures in order to improve them and design them sustainably.