Numerical analyses of water swirls in aquaculture tanks.

This article focuses on the numerical investigation of swirling water flows in aquaculture tanks with bottom drains, emphasizing the performance of various turbulence models in computational fluid dynamics (CFD) simulations. It finds that conventional two-equation eddy-viscosity turbulence models, both linear and nonlinear, tend to overpredict turbulent kinetic energy and inadequately capture swirl characteristics, whereas the Reynolds stress transport turbulence model (RSM) more accurately predicts vortex structures and the phase shift between Reynolds stress and rate-of-strain tensors. The study also examines the effects of inlet–outlet configurations and water depth on swirl formation, showing that the vertical deformation of the water funnel above the bottom drain increases linearly with the Froude number (based on outlet velocity and water depth), while horizontal deformation grows linearly with inlet velocity and exponentially with the Froude number. Additionally, the central swirling vortex consists of a forced vortex and a free vortex separated by a flow type indicator contour (λ = 0), where water velocity peaks and vertical velocity components are smaller than horizontal ones, resulting in large water residence times that may impact fish welfare.