Flow field and drag characteristics of netting of cruciform structures with various sizes of knot structure using CFD models

Abstract

The knowledge of drag characteristic and flow field around knotless and knotted cruciform patterns is very important for the design of successful netting structures. The effects of ratio between sphere (knot) and cylinder (twine) diameters (D/d) on the surrounding fluid flow and drag of cruciform structures with various attack angles was numerically investigated based on k-ω shear stress turbulent (SST) model in computational fluid dynamics (CFD) models. A finite volume method was used for solving Reynolds-averaged Navier-Stokes (RANS) equations. The results show that the effects of key parameters (attack angle, knot size) are significant on the flow pattern and drag coefficients. The drag coefficients of knotted cruciform are greater than those of knotless cruciform for one-cruciform and four-cruciform structures. The drag coefficients of one-cruciform and four-cruciform elements increased as attack angle increased. For the one-cruciform element, the knotless cruciform experienced a fewer substantial streamline detachment generating a lower drag, while knotted cruciform experienced a higher drag was because of the presence of a vortex and turbulence boundary layer flows that develops around the node causing large flow velocity reductions around it. For the four-cruciform structure, the knotted cruciform experienced a greater drag that can be attributed to a more significant development of dynamic vortex flow downstream each knot. The increase in attack angle increased the velocity reduction for four-cruciform structure, while that at downstream of one-cruciform decreased as the attack angle increased. In addition, the drag coefficient decreased as the D/d ratio increased for one-cruciform pattern, while for four-cruciform structure, it increased as the D/d ratio increased