Aerodynamics of Hummingbird Flight

人类对动物飞行机制的认识正在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的机翼运动模式来估计扑动机翼的空气动力学功能。一种名为数字粒子图像测速(DPIV)的新技术可以直接显示气流的模式，从而可以直接测量这些机翼运动产生的空气动力学机制。首席研究人员最近对DPIV进行的研究立即得出了一个令人惊讶的结果：长期以来，盘旋的蜂鸟被认为像昆虫一样对称地使用翅膀，但它们更多地依赖于下划，而不是上划。这一发现有可能完全修正鸟类盘旋的进化思想。为了扩大这一观察范围，该研究项目将通过检测近场流动来详细探索蜂鸟在悬停和低速机动时的空气动力学。这项研究将是首次在飞行鸟类中使用立体声DPIV，揭示三维流动-这一进步对于描述非定常流动模式至关重要。这些测量将允许对鸟类中是否存在非稳定空气动力学机制进行全面测试，据报道，昆虫也存在这种机制。为了确定假定的非定常机制对悬停时的力平衡的功能意义，研究人员将把观察到的3D蜂鸟运动学编程到一个动态缩放的机器人中，测试近场/远场流动模式的一致性，并测量机器人机翼周围的力矩。在机器人的近场和尾流中进行采样，将能够测试使用远场涡流-尾迹结构来估计扑动飞行期间的时间平均力的有效性。最终，这项研究的结果将提高对悬停蜂鸟在翅膀功能上与昆虫融合的程度的基本了解，完善动物飞行的机器人模拟，并确定蜂鸟稳定性和机动性的运动学和空气动力学基础。更广泛地说，这项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动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。反过来，这些计算模型可能被用来检验有关蜂鸟独特飞行方式进化的假设。本科生的合作者参与了这项跨学科研究的所有方面，这项研究中使用的DPIV仪器将促进美国各地区的合作。由于蜂鸟特别吸引公众，项目科学家将继续积极与专业艺术家和科学作家合作，通过艺术场所和大众媒体传播DPIV图像和关于蜂鸟的见解。

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.