Evaluation of fluid behavior and turnover in aquaculture tanks using CFD and transient temperature fields

This study investigates three-dimensional flow development, mixing behavior, and water turnover in an aquaculture tank using Computational Fluid Dynamics (CFD) coupled with a temperature-gradient tracer method. Cold water was continuously injected into a tank initially filled with warm water, and transient temperature gradients were used to characterize mixing and water exchange processes. A three-dimensional transient CFD model employing the Volume of Fluid (VOF) approach was validated against measurements from 20 thermocouples distributed throughout the tank. Grid-independence testing identified a 5 mm mesh as sufficient to resolve weak-flow regions and persistent stagnation beneath the inlet. The simulations captured jet-driven recirculation and the emergence of stable large-scale circulation. Flow stabilization occurred at approximately 1.0–1.5 Hydraulic Retention Time (HRT), while turnover exceeded 90% by 2.5 HRT, after which exchange rates diminished. Residual heterogeneity was confined primarily to persistent low-velocity regions beneath the inlet. These findings demonstrate that temperature-based transient CFD provides a quantitatively validated framework for diagnosing fluid performance and guiding tank design optimization. • Temperature-gradient CFD successfully visualized three-dimensional flow and turnover in an aquaculture tank. • Flow stabilized (non-steady to steady) at 1.5 HRT, and effective water renewal (> 90%) was achieved by 2.5 HRT. • Persistent stagnation (< 5% of inlet velocity) beneath the inlet limits local mixing and informs tank design optimization.