The vortex wake of blackcaps (Sylvia atricapilla L.) measured using high-speed digital particle image velocimetry (DPIV)
The vortex wake of blackcaps (Sylvia atricapilla L.) measured using high-speed digital particle image velocimetry (DPIV)
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DOI：
10.1242/jeb.034454
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发表时间：
2009-10-15
影响因子：
2.8
通讯作者：
Hedenstrom, A.
中科院分区：
文献类型：
--
作者：
Johansson, L. C.;Hedenstrom, A.
重建自由飞行的鸟类的涡流尾流是具有挑战性的，但在过去的几年里，直接测量的尾流环流已经成为一些物种。在沿鸟翼展沿着不同位置测量了流向环流，但在横向平面上没有进行测量。蝙蝠尾流研究的最新发现指出了重建尾流拓扑结构的横向平面数据的重要性，因为重要的结构可能会被错过。我们目前的高速DPIV测量结果在横向平面后面自由飞行的黑头。我们发现了新的尾流结构，以前没有显示在鸟类，包括翼根涡的相反，以及相同的标志作为翼尖涡。这表明鸟类的尾流结构比以前假设的更复杂，需要分别对翅膀和身体上的流动进行更详细的研究。基于对有尾和无尾鸟类的测量，我们还测试了关于稳定飞行过程中尾巴功能的假设。我们无法检测到有尾巴和没有尾巴的鸟类在尾流模式上的任何差异。我们的结论是，鸟类不使用他们的尾巴，以利用涡脱落在翼根在下冲程。我们也没有发现支持尾巴应该减少鸟的阻力的假设。因此，稳定飞行时尾翼的功能仍不清楚，需要在未来的研究中进一步调查。
Reconstructing the vortex wake of freely flying birds is challenging, but in the past few years, direct measurements of the wake circulation have become available for a number of species. Streamwise circulation has been measured at different positions along the span of the birds, but no measurements have been performed in the transverse plane. Recent findings from studies of bat wakes have pointed to the importance of transverse plane data for reconstructing the wake topology because important structures may be missed otherwise. We present results of high-speed DPIV measurements in the transverse plane behind freely flying blackcaps. We found novel wake structures previously not shown in birds, including wing root vortices of opposite as well as the same sign as the wing tip vortices. This suggests a more complex wake structure in birds than previously assumed and calls for more detailed studies of the flow over the wings and body, respectively. Based on measurements on birds with and without a tail we also tested hypotheses regarding the function of the tail during steady flight. We were unable to detect any differences in the wake pattern between birds with and without a tail. We conclude that the birds do not use their tail to exploit vortices shed at the wing root during the downstroke. Neither did we find support for the hypothesis that the tail should reduce the drag of the bird. The function of the tail during steady flight thus remains unclear and calls for further investigation in future studies.