Hydrodynamics of PET net panels using the Improved Delayed Detached Eddy Simulation

This study employs the Improved Delayed Detached Eddy Simulation (IDDES) method to explore the flow field distributions and hydrodynamic coefficients to further enhance the understanding of the hydrodynamic characteristics of polyethylene terephthalate (PET) nets commonly used in offshore aquaculture facilities. The study examined the effects of inflow velocity, angle of attack, and net solidity on the hydrodynamic behavior of the net panels. Capitalized on a typical case of flowing past a circular cylinder, the accuracies of the turbulence model and the solver were successfully substantiated. The results presented that the velocity fields and hydrodynamic coefficients of the 19 net-mesh panels were close to the full-scale nets. The drag coefficients gradually declined as the increase of inflow velocities. The local flow acceleration effected on both spanwise directions of twines diminish, while the downstream wake gets fully developed. Furthermore, the drag coefficients of nets present a gradual increasing tendency with net solidities, the local flow acceleration effected on both spanwise directions of twines, and the wake interactions were enhanced. The downstream streamlines converged to form a considerable region with low velocities for the case of the solidity 0.230. The drag coefficients continuously increased as the panels became more perpendicular to the flow direction, while the lift coefficients were inclined to rise initially and then decreased. The more considerable velocity reductions in addition to low flow interactions among twines were also observed. The effects of local interactions of flow fields among twines, along with the flow acceleration on both spanwise directions of twines, were the most dominant especially in the case of angle of attack 90°. This study demonstrated that both solidity and angle of attack significantly influenced the flow field distribution and hydrodynamic coefficients of PET nets. This numerical study has clarified the velocity fields and hydrodynamic coefficients around PET nets, providing the solid foundation for further analysis of the flow exchange across aquaculture structures.