Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
J R Soc Interface. 2017 Oct;14(135). doi: 10.1098/rsif.2017.0496.
Albatrosses can travel a thousand kilometres daily over the oceans. They extract their propulsive energy from horizontal wind shears with a flight strategy called dynamic soaring. While thermal soaring, exploited by birds of prey and sports gliders, consists of simply remaining in updrafts, extracting energy from horizontal winds necessitates redistributing momentum across the wind shear layer, by means of an intricate and dynamic flight manoeuvre. Dynamic soaring has been described as a sequence of half-turns connecting upwind climbs and downwind dives through the surface shear layer. Here, we investigate the optimal (minimum-wind) flight trajectory, with a combined numerical and analytic methodology. We show that contrary to current thinking, but consistent with GPS recordings of albatrosses, when the shear layer is thin the optimal trajectory is composed of small-angle, large-radius arcs. Essentially, the albatross is a flying sailboat, sequentially acting as sail and keel, and is most efficient when remaining crosswind at all times. Our analysis constitutes a general framework for dynamic soaring and more broadly energy extraction in complex winds. It is geared to improve the characterization of pelagic birds flight dynamics and habitat, and could enable the development of a robotic albatross that could travel with a virtually infinite range.
信天翁每天可以在海洋上飞行一千公里。它们利用一种被称为动力翱翔的飞行策略，从水平风切变中提取推进能量。虽然热气流翱翔被猛禽和运动滑翔机利用，但它只是简单地停留在上升气流中，而从水平风中提取能量则需要通过一种复杂而动态的飞行机动来在风切变层中重新分配动量。动力翱翔被描述为一系列半转弯，通过表面风切变层连接顺风爬升和逆风下降。在这里，我们通过数值和分析相结合的方法研究了最优（最小风）飞行轨迹。我们表明，与当前的想法相反，但与信天翁的 GPS 记录一致，当风切变层较薄时，最优轨迹由小角度、大半径的弧线组成。本质上，信天翁是一艘飞行帆船，依次充当帆和龙骨，当它始终保持横风飞行时效率最高。我们的分析构成了动力翱翔和更广泛的复杂风能量提取的一般框架。它旨在改善对海洋鸟类飞行动力学和栖息地的特征描述，并能够开发出一种能够以近乎无限的范围飞行的机器人信天翁。
