Wake Characteristics and Near-field Mass and Momentum Transport Through Fishing Net Panel

Cage-based aquaculture has been growing rapidly in recent years, which results in clustering of large quantities of cages in fish farms located in inland lakes and reservoirs and coastal embayment, and hence significantly affecting flow and mass transport in the surrounding waters. However, existing studies focus primarily on the macro-scale flow blockage effects of the fish cages, and the complex wake flow pattern and the resultant mass transport induced by the cage are yet to be studied. To address this issue, this study employs the combined particle image velocimetry-planar laser-induced fluorescence (PIV-PLIF) technique to measure the wake characteristics and the associated mass transport through the fishing net panel as the key component of the fish cage. The extent of the wake area, flow pattern transition, and vortex shedding, etc, were determined from the measured velocity field. The mechanism of the highly heterogeneous wakefield on the mass transport was theoretically analyzed using turbulent kinetic energy production and dissipation equilibrium model and diffusion scaling model. A numerical model was also developed using OpenFOAM and calibrated and validated by the experimental results, and further used to explore the dependence of the mass transport on the properties of the net panel and the flow conditions. The study is expected to assist in the assessment of the environmental impacts and environmental carrying capacity as well as the optimization of the design and deployment of cages in fish farms.