标题： 间歇性湍流阵风使鹰上升 显示英文标题

标题： Intermittent turbulent gusts lift eagles

摘要： 湍流会迫使飞机降落，而在飞行中对抗湍流需要能量，但有飞行能力的野生动物却能在多风的日子里轻松飞行。 飞行动物与短暂湍流阵风之间的相互作用性质尚不清楚，尤其是在与我们在热力或动态滑翔中对较大且稳定的气流飞行的理解相比时。 我们发现，滑翔的金雕（Aquila chrysaetos）经历了短时间的向上加速，这表明它们优先参与了强而间歇性的湍流上升气流。 垂直加速度反映了升力的变化，这些变化比平均值大25个标准差，或超过重力加速度的三倍，如此之大以至于与阵风缓解或避免不一致。 这些极端事件以短促的爆发形式出现，类似于与湍流涡旋的运动相仿。 爆发统计和它们的对称性在更长的时间尺度上接近湍流。 在最短的时间尺度上，这些爆发打破了小尺度湍流的对称性，使得向上的加速度比湍流更加间歇。 我们引入了一个简单的非线性模型，该模型可以预测对称性破坏发生的尺度以及在较小尺度上的更强间歇性。 这些发现表明了一种在湍流阵风上的棘轮机制，并构成了野生动物利用湍流阵风的第一个定量证据。 一个含义是，湍流如此强大且普遍，以至于非定常和非线性空气动力学成为大气边界层中扑翼和滑翔飞行固有且有益的方面——这一点我们需要纳入对飞行能量消耗的理解中。 显示英文摘要

摘要： Turbulence grounds aircraft and combating it in flight requires energy, yet volant wildlife fly effortlessly even on windy days. The nature of the interactions between soaring birds and transient turbulent gusts is not clear, especially when compared with our understanding of flight in larger and steadier airflows during thermal or dynamic soaring. We show that soaring golden eagles (Aquila chrysaetos) experienced short upward accelerations indicative of preferential engagement with strong and intermittent turbulent updrafts. The vertical accelerations reflect changes in lift that were as large as 25 standard deviations from the mean, or more than three times the acceleration of gravity, and so large as not to be consistent with gust mitigation or avoidance. These extreme events occurred in short bursts that mimic movement with turbulent vortices. The burst statistics and their symmetries approach those of turbulence toward longer timescales. On the shortest timescales, the bursts break the symmetry of small-scale turbulence in favor of upward accelerations that are more intermittent than turbulence. We introduce a simple nonlinear model that predicts the scale at which symmetry breaks and the stronger intermittency on the smaller scales. These findings suggest a ratcheting mechanism on turbulent gusts and constitute the first quantitative evidence in favor of turbulent gust harvesting by wildlife. An implications is that turbulence is so strong and pervasive as to make unsteady and nonlinear aerodynamics an intrinsic and beneficial aspect of both flapping and soaring flight in the atmospheric boundary layer - one that we need to incorporate in our understanding of the energetics of flight.