Abstract A biplane-type hyper-lift trawl door is newly designed to achieve stable handling while maneuvering, deploying, and stowing with excellent hydrodynamic performances for both bottom and midwater trawling. Flume-tank experiments were carried out to investigate the effect of the aspect ratio (λ, defined as the span b divided by chord c) on the hydrodynamic characteristics of the biplane-type hyper-lift trawl door with a camber ratio of 20% within a wide range of angles of attack (α). The maximum lift coefficients (CLmax) were 2.10 (λ = 1.0, α = 42°), 2.11 (λ = 1.6, α = 37°), and 2.06 (λ = 2.0, α = 28°). With a decreasing stall angle, the maximum lift coefficient remained constant (greater than 2). Considering the compactness and maneuverability of the biplane-type hyper-lift trawl door, an aspect ratio of 2 was adopted for the following experiments. The gap-chord ratio (G/c, G the gap between the fore and rear wings perpendicular to the chord direction) and stagger angle (θ, the included angle between the gap and the line connecting the leading edges of the fore and rear wings) expressing the positional relationship between the fore and rear wings of the biplane-type hyper-lift trawl door were set as 0.75, 0.9, and 1.0 and 20°, 30°, and 40°, respectively, to investigate the hydrodynamic characteristics further. The maximum lift coefficients and stall angles for the five biplane-type models were approximately 2.05 and 30°, respectively. Interestingly, these values were larger than the maximum lift coefficient and stall angle for a monoplane hyper-lift trawl door with the same aspect ratio (= 2) (CLmax = 1.78, α = 22°). This implies that the biplane-type structure contributes to enhancing the lift force and increasing the stall angle. The hydrodynamic forces of the fore and rear wings of the biplane-type hyper-lift trawl door were then calculated using a computational fluid dynamics approach. The lift coefficient for the rear wing was significantly higher than that for the fore wing before an angle of attack of 30° was reached. Nevertheless, the lift force distribution ratio for both the fore wing and the rear wing relative to the entire otter board approached 50%. On the other hand, the stall angle for the rear wing was approximately 30°, and that of the fore wing was around 38°. The fluid between the fore and rear wings tended to flow downstream and to successfully inhibit flow separation on the suction side of the fore wing.

中文翻译：

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用于水獭拖网的新设计的双翼型超升力拖网门的水动力性能

摘要 一种双翼型超升力拖网门是新设计的一种在操纵、展开和收起时实现稳定操纵的双翼型超升力拖网门，具有优良的水动力性能，适用于底拖网和中水拖网。为研究纵横比（λ，定义为跨度 b 除以弦 c）对弯度比为 20% 的双翼型超升力拖网门水动力特性的影响。大范围的攻角 (α)。最大升力系数 (CLmax) 为 2.10（λ = 1.0，α = 42°）、2.11（λ = 1.6，α = 37°）和 2.06（λ = 2.0，α = 28°）。随着失速角的减小，最大升力系数保持不变（大于 2）。考虑到双翼型超升力拖网门的紧凑性和机动性，以下实验采用纵横比 2。间隙弦比（G/c，G为前后翼垂直于弦向的间隙）和交错角（θ，间隙与前后翼前缘连线的夹角） ) 表示双翼型超升力拖网门前后翼的位置关系，分别设置为 0.75、0.9 和 1.0 和 20°、30°和 40°，以进一步研究水动力特性。五种双翼飞机模型的最大升力系数和失速角分别约为 2.05 和 30°。有趣的是，这些值大于具有相同纵横比 (= 2) (CLmax = 1.78, α = 22°) 的单翼超升力拖网门的最大升力系数和失速角。这意味着双翼型结构有助于增强升力和增加失速角。然后使用计算流体动力学方法计算双翼型超升力拖网门前后翼的水动力。在达到 30° 迎角之前，后翼的升力系数明显高于前翼。尽管如此，前翼和后翼相对于整个水獭板的升力分配比接近50%。另一方面，后翼的失速角约为 30°，前翼的失速角约为 38°。前翼和后翼之间的流体倾向于向下游流动，并成功地抑制了前翼吸力侧的流动分离。