Investigation of flow field and pollutant particle distribution in the aquaculture tank for fish farming based on computational fluid dynamics

Abstract

Hydrodynamics is important for fish survival in the aquaculture tank systems, as it can directly affect the behaviour of farmed fish and the self-cleaning property of culture tank systems. The present study designs a new tank configuration, rectangular single-side arc angle tanks, to improve the performance of aquaculture vessels. The tank hydrodynamics was investigated by solving the Reynolds-Averaged Navier–Stokes (RANS) equations and combined with the discrete phase model (DPM) model to study particle motion. The velocity at the monitoring point and the discharge rate of particles from the tank were separately measured using Acoustic Doppler Velocimetry and the MATLAB image recognition method to validate the numerical model. We numerically tested the effect of culture tank configurations and the horizontal distance from the inlet pipe to the sidewall on hydrodynamics parameters, including velocity magnitude and uniformity, turbulence region and vortex distribution. Subsequently, to further understand the self-cleaning property of the culture tank systems for settleable particles, 300 cylindrical particles with a uniform size of 2.5 mm are tracked in the Lagrangian frame. Meanwhile, velocity distribution and pressure gradient have been employed to quantitatively evaluate the effects of hydrodynamics on the collection and discharge regularity of particles. Through CFD-assisted design verification, the tank configuration and the position of the inlet pipe layout have a considerable impact on the removal of particles from the tank and the energy to sustain the flow in the tank. Some key findings are found that 1) the hydrodynamics was improved significantly after rounding two right-angle edges in the rectangular culture tank, in which the configuration tanks of η = 0.2 and η = 0.3 could establish the strengthened rotational flow with better uniformity; 2) the inlet pipes proper far from the sidewall can enhance the self-cleaning property of the tank and the inlet pipe layout position of δ = 0.02–0.04 is the preferred interval.