Numerical simulation of nodule mesh hydrodynamics based on CFD

Abstract

With the rapid advancement of the aquaculture industry, deep-sea aquaculture has become the primary development direction for ocean-based fish farming. As the key structural barrier that protects cultured species, the netting system plays a critical role in determining the hydrodynamic performance and operational stability of aquaculture cages. In particular, understanding the hydrodynamic loading and flow-around characteristics of mesh structures is essential for optimizing net design and ensuring structural resilience under various environmental conditions. In this study, the hydrodynamic loading and flow bypassing characteristics of small-scale nodular mesh structures were investigated using computational fluid dynamics (CFD) simulations, with the aim of revealing the influence of key structural and flow parameters on their hydrodynamic behavior. The numerical results indicate that the drag coefficient reaches its maximum at an angle of attack (AOA) of 90°. Within the range of 45° to 90° AOA, the T0 knotted mesh exhibits a higher drag coefficient than the T45 configuration. In contrast, between 0° and 45° AOA, the T0 mesh yields lower drag compared to T45. Regarding lift characteristics, the maximum lift coefficient occurs near 45° AOA and decreases progressively as the AOA approaches 0° or 90°. At all tested angles, the T0 mesh consistently demonstrates a higher lift coefficient than the T45 mesh. An increase in mesh solidity leads to a reduction in drag coefficient. Additionally, variations in twine diameter have a more pronounced effect on the drag performance of the knotted mesh than changes in twine length. The presence of knots significantly extends the wake region downstream of the cross-flow area. As the AOA decreases, the extent of the low-velocity wake behind the knotted mesh diminishes. Moreover, modifying mesh compactness by altering twine diameter has a greater influence on the surrounding flow field, local velocity gradients, and pressure distribution than changes in twine length.