Symmetry breaking leads to forward flapping flight
Symmetry breaking leads to forward flapping flight
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DOI：
10.1017/s0022112004008468
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发表时间：
2004-05-10
影响因子：
3.7
通讯作者：
Childress, S
中科院分区：
文献类型：
--
作者：
Vandenberghe, N;Zhang, J;Childress, S
扑翼飞行在自然界中普遍存在，然而在微生物世界中，盛行的是纤毛和鞭毛，而非翅膀。本文探讨了这种二分现象。我们通过实验研究了一个上下扑动且可自由水平移动的翅膀的动力学。当超过一个临界频率时，翅膀开始自发向前移动，这表明“扑翼飞行”是从无水平运动的纯扑动状态发生的一种对称性破缺分岔。一个无量纲参数，即基于扑动频率的雷诺数，表征了分岔点。在这个分岔点之上，我们观察到前进速度随扑动频率线性增加。对上下起伏的翼片周围流场的可视化显示，在转变点之下是一种对称模式。在阈值之上，在翅膀尾流中观察到一个反向的冯·卡门涡街。我们的模型实验结果，即临界雷诺数和阈值之上的行为，与对游泳和飞行动物基于扑翼的运动的观察结果是一致的。
Flapping flight is ubiquitous in Nature, yet cilia and flagella, not wings, prevail in the world of micro-organisms. This paper addresses this dichotomy. We investigate experimentally the dynamics of a wing, flapped up and down and free to move horizontally. The wing begins to move forward spontaneously as a critical frequency is exceeded, indicating that 'flapping flight' occurs as a symmetry-breaking bifurcation from a pure flapping state with no horizontal motion. A dimensionless parameter, the Reynolds number based on the flapping frequency, characterizes the point of bifurcation. Above this bifurcation, we observe that the forward speed increases linearly with the flapping frequency. Visualization of the flow field around the heaving and plunging foil shows a symmetric pattern below transition. Above threshold, an inverted von Karman vortex street is observed in the wake of the wing. The results of our model experiment, namely the critical Reynolds number and the behaviour above threshold, are consistent with observations of the flapping-based locomotion of swimming and flying animals.