Hydrodynamic analysis of fish swimming behavior in turbulent river confluences

This study focuses on selecting the most appropriate turbulence model for simulating fish swimming behavior in river confluences. To achieve this, three numerical models—k-ε, k-ω, and large eddy simulation—were compared by running simulations under identical flow conditions and evaluating the results against biological experimental data. Among the models, the k-ω model demonstrated the smallest relative error, consistently within 5% of the experimental results, confirming its superior accuracy and reliability for this application. The k-ω model's ability to capture boundary layer turbulence and near-wall flow dynamics proved essential for studying fish swimming in complex turbulent environments. Simulations revealed that both the flow velocity ratio between the main stream and tributary and the confluence angle are critical factors influencing the flow structure. At higher flow velocity ratios (R = 1/3 and 3/1) or large confluence angles (α ≥ 90°), turbulence intensity increased, leading to more complex vortex formations that significantly impacted fish swimming speed. When the flow velocity ratio (R) is 1/3, the fish can achieve a maximum swimming speed of 2.75 L/s, which is significantly higher than the swimming speed of 1.18 L/s observed when R is 3/1. Additionally, fish closer to the center of the flow field experienced greater turbulence, resulting in higher energy expenditure. The findings provide crucial insights into the hydrodynamic mechanisms driving fish swimming behavior in dynamic aquatic environments.