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首页> 美国卫生研究院文献>Journal of the Royal Society Interface >Vortex wake downwash distribution aerodynamic performance and wingbeat kinematics in slow-flying pied flycatchers
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Vortex wake downwash distribution aerodynamic performance and wingbeat kinematics in slow-flying pied flycatchers

机译：慢速飞行捕蝇器的涡流尾流下冲分布空气动力性能和机翼运动学

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Many small passerines regularly fly slowly when catching prey, flying in cluttered environments or landing on a perch or nest. While flying slowly, passerines generate most of the flight forces during the downstroke, and have a ‘feathered upstroke’ during which they make their wing inactive by retracting it close to the body and by spreading the primary wing feathers. How this flight mode relates aerodynamically to the cruising flight and so-called ‘normal hovering’ as used in hummingbirds is not yet known. Here, we present time-resolved fluid dynamics data in combination with wingbeat kinematics data for three pied flycatchers flying across a range of speeds from near hovering to their calculated minimum power speed. Flycatchers are adapted to low speed flight, which they habitually use when catching insects on the wing. From the wake dynamics data, we constructed average wingbeat wakes and determined the time-resolved flight forces, the time-resolved downwash distributions and the resulting lift-to-drag ratios, span efficiencies and flap efficiencies. During the downstroke, slow-flying flycatchers generate a single-vortex loop wake, which is much more similar to that generated by birds at cruising flight speeds than it is to the double loop vortex wake in hovering hummingbirds. This wake structure results in a relatively high downwash behind the body, which can be explained by the relatively active tail in flycatchers. As a result of this, slow-flying flycatchers have a span efficiency which is similar to that of the birds in cruising flight and which can be assumed to be higher than in hovering hummingbirds. During the upstroke, the wings of slowly flying flycatchers generated no significant forces, but the body–tail configuration added 23 per cent to weight support. This is strikingly similar to the 25 per cent weight support generated by the wing upstroke in hovering hummingbirds. Thus, for slow-flying passerines, the upstroke cannot be regarded as inactive, and the tail may be of importance for flight efficiency and possibly manoeuvrability.
机译：许多小pass鱼在捕获猎物，在混乱的环境中飞行或降落在栖息处或巢穴时会定期缓慢飞行。在缓慢飞行的过程中，雀形目鸟会在向下冲程中产生大部分飞行力，并具有“羽化向上冲程”，在此过程中，机翼会缩回身体并散布主要机翼的羽毛，从而使机翼失去作用。这种飞行模式在空气动力学上与巡航飞行以及蜂鸟使用的所谓“正常盘旋”之间的关系还不清楚。在这里，我们给出了时间分辨的流体动力学数据，并结合了翼状运动捕捉器的机翼运动学数据，这些飞行器在从接近悬停到计算出的最小动力速度的速度范围内飞行。捕蝇器适合低速飞行，在机翼上捕捉昆虫时通常会使用这种捕蝇器。从尾流动力学数据中，我们构造了平均机翼节拍尾流，并确定了时间分辨的飞行力，时间分辨的下冲分布以及所产生的升阻比，跨度效率和襟翼效率。在下风期间，慢飞的捕蝇器会产生一个单涡流环流尾流，这与以巡航速度飞行的鸟类所产生的单涡流环流相比，与在蜂鸟盘旋时的双环涡流尾流相类似。这种尾流结构导致身体后部的下冲较高，这可以用捕蝇器中相对活跃的尾巴来解释。结果，缓慢飞行的捕蝇器的跨度效率与巡航飞行中的鸟类类似，可以认为比盘旋的蜂鸟更高。在上冲程期间，缓慢飞行的捕蝇器的机翼没有产生很大的作用力，但其尾巴结构使重量支撑增加了23％。惊人的是，这类似于盘旋蜂鸟时机翼上行程产生的25％的重量支撑。因此，对于慢速飞行的er鱼来说，上冲程不能被认为是无效的，尾巴对于飞行效率和可能的机动性可能很重要。

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