Investigating Flow Regimes and Bed-Shear Stress Patterns Around Aquaculture Elements Using CFD

Marine aquaculture structures alter local hydrodynamics through flow deflection, wake formation, and changes in near-bed shear stress, with potential implications for water exchange, benthic conditions, site selection, and environmental assessment. This study applies a three-dimensional unsteady Reynolds-averaged Navier–Stokes computational fluid dynamics framework to investigate how idealised fish-cage configurations influence flow fields, wake persistence, and kinematic bed shear stress. The numerical implementation was first benchmarked against analytical potential-flow solutions for single and multiple cylinders, with a mean relative velocity error of 1.47% for the benchmark cases. Farm-scale simulations represented circular cages using 38 m diameter discs and examined the effects of inlet velocity, cage diameter, layout, farm size, cage spacing, seabed roughness, and biofouling. Increased inlet velocity generated the largest single-cage bed-stress response, increasing peak kinematic bed shear stress by 139% relative to the medium-velocity baseline. Farm layout strongly affected wake persistence: a linear nine-cage arrangement increased wake length by 354% relative to the grid baseline, whereas staggered and honeycomb layouts reduced wake length. Biofouling increased peak bed shear stress by up to 24%, while larger cages and farms produced more persistent downstream disturbances. No scenario exceeded the adopted bed shear-stress threshold for sediment mobility. The results demonstrate that a computationally efficient, numerically verified, idealised Computational Fluid Dynamics (CFD)framework can support comparative assessment of relative trends across aquaculture farm layouts and operational conditions, informing sustainable farm design, environmental assessment, and marine spatial planning.