Resistance performance and fluid-flow investigation of trawl plane netting at small angles of attack

Abstract

Hydrodynamic experiments in a flume tank in the current range of 40–80 cm/s and computational fluid dynamic (CFD) analysis at the current of 60 cm/s of trawl plane nettings with solidity ratios of 0.06–0.32 at small angles of attack (0–25°) were conducted to refine the understanding of the relationship between resistance performance and flow behavior. The rigid model representing the plane netting in a taut configuration was adopted. A finite volume method was used for solving Reynolds-Averaged Navier-Stokes equations associated with the shear-stress transport k-ω model in CFD analysis. Referred to experimental results, the parallel drag coefficient decreases from 0.4 to 0.25 with a reduction of 38% but, the drag coefficient at the angle of attack of 25° rises from 0.62 to 0.79 with an increment of 27% as the solidity ratio increases from 0.06 to 0.32. Such dual effect of the solidity ratio on the drag coefficient of plane nettings with respect to the inclination angle is also observed from CFD analysis. A transition of flow behavior from flowing above to passing through the netting occurs. The changing tendency of the local flow velocity is consistent with the resistance performance relative to the solidity ratio for the tested nettings.