Mechanical power curve measured in the wake of pied flycatchers indicates modulation of parasite power across flight speeds
Mechanical power curve measured in the wake of pied flycatchers indicates modulation of parasite power across flight speeds
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DOI：
10.1098/rsif.2017.0814
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发表时间：
2018-01-01
影响因子：
3.9
通讯作者：
Hedenstrom, Anders
中科院分区：
文献类型：
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作者：
Johansson, L. Christoffer;Maeda, Masateru;Hedenstrom, Anders
动物飞行所需的空气动力随飞行速度的变化决定了觅食和迁徙飞行的最佳速度。尽管与此相关，但空气动力提供了一个难以捉摸的量来直接在动物飞行中进行测量。在这里，我们用层析粒子图像测速仪测量了在风洞中自由飞行的捕蝇器的尾流速度场，从而确定了气动功率。我们发现了一条浅的U型功率曲线，这比理论上预期的要平坦。根据鸟的体角随速度的变化，我们推测，较浅的曲线是由于较低飞行速度下身体阻力系数和身体前额面积增加所致。与传统模型相比，在模型中引入了身体阻力的调整，使得数据的拟合更加合理。从尾迹结构中，我们还发现在飞行速度(1-9m S(-1))范围内，双翼在下划过程中产生了单一的起始涡。这是通过手臂翅膀在下划开始时相互作用，在鸟的身体上方产生一个统一的起始涡流来实现的。我们认为这是一种机制，导致了相当均匀的下洗和较低的诱导功率，这可以帮助解释鸟类比蝙蝠具有更高的空气动力学性能。
How aerodynamic power required for animal flight varies with flight speed determines optimal speeds during foraging and migratory flight. Despite its relevance, aerodynamic power provides an elusive quantity to measure directly in animal flight. Here, we determine the aerodynamic power from wake velocity fields, measured using tomographical particle image velocimetry, of pied flycatchers flying freely in a wind tunnel. We find a shallow U-shaped power curve, which is flatter than expected by theory. Based on how the birds vary body angle with speed, we speculate that the shallow curve results from increased body drag coefficient and body frontal area at lower flight speeds. Including modulation of body drag in the model results in a more reasonable fit with data than the traditional model. From the wake structure, we also find a single starting vortex generated from the two wings during the downstroke across flight speeds (1-9 m s(-1)). This is accomplished by the arm wings interacting at the beginning of the downstroke, generating a unified starting vortex above the body of the bird. We interpret this as a mechanism resulting in a rather uniform down-wash and low induced power, which can help explain the higher aerodynamic performance in birds compared with bats.