Aerodynamics of Hummingbird Flight

人类对动物飞行机制的理解正进入一个令人兴奋的新阶段。在过去的一个世纪里，许多研究试图通过高速胶片和视频测量翅膀运动的模式来估计扑翼的气动功能。一项新技术，数字粒子图像测速（DPIV）直接揭示气流模式，从而允许直接测量由这些机翼运动产生的空气动力学机制。从首席研究员最近的DPIV研究中立即出现了一个令人惊讶的结果，即盘旋的蜂鸟，长期以来被认为以类似昆虫的对称方式使用它们的翅膀，更多地依赖于它们的向下拍打而不是向上拍打。这一发现有可能彻底改变人们对鸟类悬停进化的看法。为了扩展这一观察，本研究项目将通过检查近场流来详细探索蜂鸟悬停和慢速机动的空气动力学。这项研究将首次使用立体DPIV在飞行的鸟类中，揭示三维流动-这对表征非定常流动模式至关重要。这些测量将允许对鸟类中存在的非定常空气动力学机制进行全面的测试，这已经在昆虫中得到了报道。为了确定假定的非定常机制对悬停力平衡的功能意义，研究人员将观察到的三维蜂鸟运动学编程到一个动态比例的机器人中，测试近场/远场流模式的一致性，并测量作用在机器人机翼上的力矩。在机器人的近场和尾迹中进行采样，将能够测试使用远场涡-尾迹结构来估计扑翼飞行期间的时间平均力的有效性。最终，本研究结果将提高对悬停蜂鸟与昆虫在翅膀功能上趋同程度的基本认识，完善动物飞行的机器人模拟，确定蜂鸟稳定性和机动性的运动学和气动基础。更广泛地说，该研究将阐明非定常和准定常空气动力学的生物操纵，从而为工程师开发自主微型飞行器提供有用的模型，并为计算流体动力学家提供精确的运动学和DPIV数据，以纳入蜂鸟飞行模型。计算模型可以反过来用来测试关于蜂鸟独特飞行方式进化的假设。本科生合作者参与了这项跨学科研究的各个方面，本研究中使用的DPIV仪器将促进美国各地区的合作。由于蜂鸟特别能引起公众的极大兴趣，项目科学家将继续与专业艺术家和科学作家积极合作，通过艺术场所和大众媒体传播DPIV图像和对蜂鸟的见解。

Human understanding of the mechanisms of animal flight is entering into an exciting new phase. Over the past century, many studies have sought to estimate the aerodynamic function of flapping wings from patterns of wing motion measured using high-speed film and video. A new technique, digital particle image velocimetry (DPIV) directly reveals patterns of airflow, and thereby permits direct measurement of the aerodynamic mechanisms produced by these wing movements. A surprising result that immediately emerged from the recent DPIV studies of the principal investigator is that hovering hummingbirds, long thought to use their wings in a symmetrical manner similar to insects, depend much more upon their downstroke than their upstroke. This finding has the potential to completely revise thinking about the evolution of hovering in birds. To extend this observation, this research project will explore in detail the aerodynamics of hovering and slow-speed maneuvering in hummingbirds by examining near-field flow. This research will be the first use of stereo DPIV in flying birds, revealing flow in three dimensions - an advance vital for characterizing unsteady flow patterns. These measurements will allow full tests for the presence of unsteady aerodynamic mechanisms in birds, which have been reported for insects. To determine the functional significance of putative unsteady mechanisms to the force balance in hovering, the investigators will program observed 3D hummingbird kinematics into a dynamically scaled robot, test for the congruence in near-field/far field flow patterns, and measure moments acting about the wing of the robot. Sampling in the near field and wake of the robot will enable tests of the validity of using far field vortex-wake structures to estimate time-averaged forces during flapping flight. Ultimately, the results of this research will improve basic understanding of the extent to which hovering hummingbirds converge with insects in wing function, refine robotic simulations of animal flight, and determine the kinematic and aerodynamic basis of stability and maneuverability in hummingbirds. More broadly, the research will elucidate biological manipulation of unsteady and quasi-steady aerodynamics, thereby providing engineers with a useful model for the development of autonomous micro-air vehicles, and providing computational fluid dynamicists with precise kinematic and DPIV data to incorporate into models of hummingbird flight. The computational models may, in turn, be used to test hypotheses regarding the evolution of hummingbird's unique flight style. Undergraduate collaborators are involved in all aspects of this cross-disciplinary research, and the DPIV instrumentation used in this study will foster collaborations across regions of the United States. Because hummingbirds in particular generate great public fascination, the project scientists will continue active collaboration with professional artists and science writers to disseminate DPIV images and insights about hummingbirds through artistic venues and the popular press.