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Aerodynamics of the hovering hummingbird

机译：徘徊的蜂鸟的空气动力学

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Despite profound musculoskeletal differences, hummingbirds (Trochilidae) are widely thought to employ aerodynamic mechanisms similar to those used by insects. The kinematic symmetry of the hummingbird upstroke and downstroke(1-3) has led to the assumption that these halves of the wingbeat cycle contribute equally to weight support during hovering, as exhibited by insects of similar size(4). This assumption has been applied, either explicitly or implicitly, in widely used aerodynamic models(1,5-7) and in a variety of empirical tests(8,9). Here we provide measurements of the wake of hovering rufous hummingbirds (Selasphorus rufus) obtained with digital particle image velocimetry that show force asymmetry: hummingbirds produce 75% of their weight support during the downstroke and only 25% during the upstroke. Some of this asymmetry is probably due to inversion of their cambered wings during upstroke. The wake of hummingbird wings also reveals evidence of leading-edge vortices created during the downstroke, indicating that they may operate at Reynolds numbers sufficiently low to exploit a key mechanism typical of insect hovering(10,11). Hummingbird hovering approaches that of insects, yet remains distinct because of effects resulting from an inherently dissimilar-avian-body plan.
机译：尽管肌肉骨骼方面存在着巨大差异，但人们广泛认为蜂鸟（Trochilidae）采用的空气动力学机制与昆虫所使用的类似。蜂鸟上冲程和下冲程的运动学对称性（1-3）导致了这样一个假设，即像相似大小的昆虫（4）所展示的，这两个半拍打周期的翼拍对悬停过程中的重量支撑有同等的作用。在广泛使用的空气动力学模型（1,5-7）和各种经验测试（8,9）中，已明确或隐含地采用了该假设。在这里，我们提供了通过数字粒子图像测速技术获得的盘旋的红褐色蜂鸟（Selasphorus rufus）的唤醒力的测量结果，显示了力的不对称性：蜂鸟在向下冲程中产生75％的重量支撑，而在向上冲程中仅产生25％的重量支撑。这种不对称性的某些原因可能是由于上冲程期间其弧形机翼的倒置。蜂鸟翅膀的唤醒也揭示了在下冲程期间产生的前沿涡旋的迹象，表明它们可能以足够低的雷诺数运行以利用昆虫盘旋的典型关键机制（10,11）。蜂鸟的盘旋接近昆虫的盘旋，但由于与生俱来的禽体计划的不同，其影响仍然很明显。

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