Scale effect of applying Tauti's law in model experiment: CFD models for flow across planar netting

Tauti's similarity criterion is the core problem in physical experiments and is associated with the accuracy of the final estimation of physical system results. In this study, a computational fluid dynamics (CFD) simulation study related to the steady fluid hydrodynamic forces acting on netting was performed by solving Reynolds-averaged Navier–Stokes equations. First, the prediction accuracy of the netting hydrodynamic forces in a flume tank was investigated. Subsequently, the basic characteristics of CFD simulations to reproduce the flow field and the hydrodynamics of a prototype net were studied. The flow field around the netting was analysed using five different schemes. When a same scale ratio was adopted (λ = λ′ = λ″, where λ is the large-scale ratio, and λ′ and λ″, are the small-scale ratios of the mesh length and twine diameter, respectively), the results demonstrate that as the scale ratio increases, the drag coefficient of the netting increases, and the relative error between the drag restored by the Tauti criterion and the original netting drag force also increases. When adopting a double different scale ratio (λ,λ′=λ″) in the schemes of the prototype netting, the drag coefficient of the netting decreased with an increase in the scale ratio, and the drag value gradually deviated from the standard value. When thress different scale ratios (λ,λ′,λ″) were adopted under various mesh sizes and twine diameters, the flow velocity reduction trend downstream of the netting was opposite to that upstream, verifying that the same small-scale ratio is accurate for the reduction result. Finally, we confirmed the improvement in the selection of the scale ratio of the Tauti criterion and the correction suggestions after adopting the scale ratio. The aforementioned findings can provide a theoretical guidance for the physical testing and design of fishing gear.