Hydrodynamic performance and flow field visualization of hyperboloid otter board

The otter board is one of the important attachments in the trawl operation system; the hydrodynamic performance is directly related to the expansion of the trawl mouth and affects its production effect and economic benefits. Hyperboloid otter board is widely used in the mid-layer trawl fishery off the Japan coast due to the high lift. The author used the single factor test method to study the hydrodynamic performance of hyperboloid model otter boards using the flume experiment and numerical simulation (Computational Fluid Dynamics, CFD) with different aspect ratios λ (2.5, 3, 3.5, 4), camber ratio f/C (10%, 15%, 20%) and sweepback angle Λ (0°, 10°, 15°), analyze the hydrodynamic performance of the otter boards with different structural parameters, compare the results of the two methods, and visualize the flow field around the otter board. The results show: (1) No.2 otter board (λ=3, f/C=15%, Λ=10°) has the highest lift coefficient when the angle of attack is 25°, the model experiment value is 1.7, the simulation value is 1.88, and the drag coefficient increases with the increase of the angle of attack, the average deviation of the simulated and measured values of the flow velocity at the back is 4.4%, and the results obtained by the two methods are highly consistent (P<0.01). (2) In the flow field distribution, the separation point of the boundary layer of No.2 otter board moved with the increase of the angle of attack and gradually moved to the leading edge of the fore wing, the rear vortex of the central plane increased with the increase of the angle of attack, and the left side low pressure zone increased first and then decreased with the increase of the angle of attack, and the tail of the otter board increased with the angle to form a distinct wing tip vortex, which produced vortex lift to provide additional lift to the otter board, making hyperboloid have higher lift than other types otter board. The results of this study have reference value for the development of the otter board or optimized otter board performance.