Warrick Douglas R, Tobalske Bret W, Powers Donald R
Department of Zoology, Oregon State University, 3029 Cordley Hall, Corvallis, Oregon 97331, USA.
Nature. 2005 Jun 23;435(7045):1094-7. doi: 10.1038/nature03647.
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 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. This assumption has been applied, either explicitly or implicitly, in widely used aerodynamic models and in a variety of empirical tests. 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. Hummingbird hovering approaches that of insects, yet remains distinct because of effects resulting from an inherently dissimilar-avian-body plan.
尽管蜂鸟（蜂鸟科）在肌肉骨骼方面存在显著差异，但人们普遍认为它们采用的空气动力学机制与昆虫相似。蜂鸟上下拍动翅膀的运动学对称性导致了这样一种假设，即翅膀拍动周期的这两个部分在悬停时对支撑体重的贡献相同，类似大小的昆虫就是如此。这个假设已经被明确或隐含地应用于广泛使用的空气动力学模型以及各种实证测试中。在这里，我们提供了用数字粒子图像测速技术获得的红喉北蜂鸟（红喉北蜂鸟）悬停尾流的测量结果，这些结果显示了力的不对称性：蜂鸟在下拍过程中产生其体重支撑的75%，而在上拍过程中仅产生25%。这种不对称性部分可能是由于它们向上拍动时弧形翅膀的翻转。蜂鸟翅膀的尾流还揭示了下拍过程中产生的前缘涡的证据，这表明它们可能在足够低的雷诺数下运行，以利用昆虫悬停的一种典型关键机制。蜂鸟的悬停方式接近昆虫，但由于其固有的不同鸟类身体结构所产生的影响，仍然有所不同。
