Study of the Influence of Aspect Ratios on Hydrodynamic Performance of a Symmetrical Elliptic Otter Board

Abstract

The otter board, which is designed to maintain the horizontal opening of trawl nets, is a vital component of a trawl system. It requires a high lift-to-drag ratio, which is directly related to the trawling efficiency and economic effectiveness of the single trawler. To improve the hydrodynamic efficiency of a symmetrical elliptic otter board, four model otter boards, i.e., aspect ratio (AR) = 0.507, 0.640, 0.766, and 0.895, were designed in the present work and the effects of aspect ratios on the hydrodynamic performance of the otter board were investigated by flume tank experiments. Further, the k-ε EARSM turbulence model was adopted to analyze the hydrodynamic coefficients and the flow distribution around the otter board using the computational fluid dynamics (CFD) method. The optimal aspect ratio was obtained based on the analysis of experimental data, wherein the lift coefficient, the drag coefficient, and the lift-to-drag ratio at different angles of attack (AOA) were measured. The results show that the symmetrical elliptic otter board model is within the critical Reynolds number region when the Reynolds number is larger than 1.682 × 105, and its hydrodynamic coefficient is consistent with the real otter board. When the AR was 0.766, the elliptic otter board had the best hydrodynamic performance, of which the lift coefficient and the lift-to-drag ratio were 1.05 and 1.14 fold that of the initial otter board (AR = 0.640), and the volume of the wing-tip vortex reaches a maximum. The results show the hydrodynamic performance of the symmetrical elliptic otter board, and parameter optimization of the otter board has also been provided for reference.