标题： 间歇性的湍流阵风抬升了老鹰 显示英文标题

标题： Intermittent turbulent gusts lift eagles

摘要： 湍流使飞机无法起飞并在飞行中需要消耗能量，然而会飞的野生动物却能在多风的日子里轻松飞行。 翱翔鸟类与短暂湍流气流之间的相互作用性质尚不清楚，尤其是与我们对热气流或动态滑翔过程中更大且更稳定的气流中的飞行理解相比。 我们发现，翱翔的金雕（Aquila chrysaetos）经历了短暂的向上加速度，这表明它们倾向于与强烈的间歇性湍流上升气流相互作用。 这些垂直加速度反映了升力的变化，其变化幅度高达平均值的25个标准差，或者超过重力加速度的三倍，因此不可能仅仅归因于气流扰动的缓解或规避。 这些极端事件以短促爆发的形式出现，类似于与湍流涡旋运动相匹配的方式。 在较长时间尺度上，这些爆发统计特性和对称性接近湍流特性。 在最短时间尺度上，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性。 我们提出了一种简单的非线性模型，该模型可以预测对称性破坏的尺度以及较小尺度上的更强间歇性。 这些发现表明湍流气流存在一种“棘轮机制”，并且首次提供了野生生物利用湍流气流的定量证据。 由此得出的一个含义是，湍流如此强烈且普遍存在，以至于不稳定性与非线性空气动力学成为大气边界层中扑翼和翱翔飞行固有的、有益的特征——这是我们理解飞行能量消耗时需要纳入的因素。 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 implication 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.