Aerodynamic forces and vortical structures in flapping butterfly's forward flight
Aerodynamic forces and vortical structures in flapping butterfly's forward flight
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DOI：
10.1063/1.4790882
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发表时间：
2013-02-01
影响因子：
4.6
通讯作者：
Hirai, Norio
中科院分区：
文献类型：
--
作者：
Yokoyama, Naoto;Senda, Kei;Hirai, Norio
对双侧对称扑动蝴蝶的向前飞行进行了数值模拟，该蝴蝶被建模为由胸部、腹部和左右翅膀组成的四连杆刚体系统。蝴蝶的关节运动是根据实验观察采用的。进行了三种模拟，根据确定胸部位置和姿态的方式进行区分：系留模拟、规定模拟和自由飞行模拟。系留模拟中蝴蝶胸部固定的向上力和顺流向力以及尾流结构与相应系留实验中的结果相当一致。在规定的模拟中，胸部轨迹和关节角度是根据自由飞行实验中观察到的给出的，证实蝴蝶可以产生足够的力来实现扑翼飞行。此外，还识别出了尾流和机翼上的相干涡旋结构。由于涡流结构而产生的空气动力也得到了阐明。在自由飞行模拟中，仅给出关节角度作为时间的周期函数，发现自由飞行是纵向不稳定的，因为蝴蝶无法将姿态保持在适当的范围内。重点关注腹部质量，其由于进食和代谢而变化很大，我们发现腹部运动在周期性飞行中起着重要作用。还讨论了周期性飞行和机动性控制胸部姿态的必要性。 (C) 2013 年美国物理研究所。 [http://dx.doi.org/10.1063/1.4790882]
Forward flights of a bilaterally symmetrically flapping butterfly modeled as a four-link rigid-body system consisting of a thorax, an abdomen, and left and right wings are numerically simulated. The joint motions of the butterflies are adopted from experimental observations. Three kinds of the simulations, distinguished by ways to determine the position and attitude of the thorax, are carried out: a tethered simulation, a prescribed simulation, and free-flight simulations. The upward and streamwise forces as well as the wake structures in the tethered simulation, where the thorax of the butterfly is fixed, reasonably agree with those in the corresponding tethered experiment. In the prescribed simulation, where the thoracic trajectories as well as the joint angles are given by those observed in a free-flight experiment, it is confirmed that the butterfly can produce enough forces to achieve the flapping flights. Moreover, coherent vortical structures in the wake and those on the wings are identified. The generation of the aerodynamic forces due to the vortical structures are also clarified. In the free-flight simulation, where only the joint angles are given as periodic functions of time, it is found that the free flight is longitudinally unstable because the butterfly cannot maintain the attitude in a proper range. Focusing on the abdominal mass, which largely varies owing to feeding and metabolizing, we have shown that the abdominal motion plays an important role in periodic flights. The necessity of control of the thoracic attitude for periodic flights and maneuverability is also discussed. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790882]