You’re on an airplane when you feel a sudden jolt. Outside your window nothing seems to be happening, yet the plane continues to rattle you and your fellow passengers as it passes through turbulent air in the atmosphere.
你在飞机上, 突然感到一阵颠簸。 你往窗外看外, 似乎什么都没有发生, 可是持续的颠簸 让你和其他乘客感到不安,
Although it may not comfort you to hear it, this phenomenon is one of the prevailing mysteries of physics. After more than a century of studying turbulence, we’ve only come up with a few answers for how it works and affects the world around us.
因为飞机正在通过大气中的乱流。 虽然听起来不会让你欣慰, 这个现象是依旧是 一个广为流传的物理谜团。 在对乱流进行了一个多世纪的研究后, 我们只找到了几个解释,
And yet, turbulence is ubiquitous, springing up in virtually any system that has moving fluids. That includes the airflow in your respiratory tract. The blood moving through your arteries. And the coffee in your cup, as you stir it. Clouds are governed by turbulence, as are waves crashing along the shore and the gusts of plasma in our sun. Understanding precisely how this phenomenon works would have a bearing on so many aspects of our lives.
关于它的背后机理以及它对世界的影响。 尽管如此,乱流无处不在, 几乎在任何流体系统中都会出现。 包括你呼吸道里的气流, 你血管里流淌的血液, 和你在搅拌的咖啡里。 云是被乱流支配的,同样的, 拍打着海岸的海浪以及 带离子体的太阳风也是。 如果能准确的理解这个原理,
Here’s what we do know. Liquids and gases usually have two types of motion: a laminar flow, which is stable and smooth; and a turbulent flow, which is composed of seemingly unorganized swirls. Imagine an incense stick. The laminar flow of unruffled smoke at the base is steady and easy to predict. Closer to the top, however, the smoke accelerates, becomes unstable, and the pattern of movement changes to something chaotic. That’s turbulence in action, and turbulent flows have certain characteristics in common.
会对我们生活的方方面面 产生很大的影响。 这些是我们目前所知道的。 液体和气体一般会有两种动态: 稳定平滑的称为层流, 和看似无规律的漩涡 而组成的称为紊流。 想象一炷熏香, 层流存在于烟雾基部, 稳定并且可预测。 可是越接近烟雾的上层 由于烟雾加速, 变得非常不稳定, 运动模式也变的混乱。 这就是乱流,
Firstly, turbulence is always chaotic. That’s different from being random. Rather, this means that turbulence is very sensitive to disruptions. A little nudge one way or the other will eventually turn into completely different results. That makes it nearly impossible to predict what will happen, even with a lot of information about the current state of a system.
乱流有几个共同的特征。 第一,乱流是混乱的。 这与随机不同。 更准确来说,乱流对扰乱非常敏感。 随意的轻轻一推 就会导致完全不同的结果。 这就导致几乎无法预测会发生什么,
Another important characteristic of turbulence is the different scales of motion that these flows display. Turbulent flows have many differently-sized whirls called eddies, which are like vortices of different sizes and shapes. All those differently-sized eddies interact with each other, breaking up to become smaller and smaller until all that movement is transformed into heat, in a process called the “energy cascade."
即便有很多系统当前状态的信息。 乱流的另一个重要的特征是 表现出来的不同运动规模。 乱流有很多不同大小的漩涡 名为涡流, 它们像是不同大小的涡旋。 这些不同大小的涡流互相影响, 变得越来越小, 直到这些动能转换成热能,
So that’s how we recognize turbulence– but why does it happen? In every flowing liquid or gas there are two opposing forces: inertia and viscosity. Inertia is the tendency of fluids to keep moving, which causes instability. Viscosity works against disruption, making the flow laminar instead. In thick fluids such as honey, viscosity almost always wins. Less viscous substances like water or air are more prone to inertia, which creates instabilities that develop into turbulence.
这个过程叫做“能量串级”。 这就是我们如何辨认乱流, 可是它为什么会发生呢? 每一种流动液体或气体 都有两个相斥的力量: 惯性力与粘滞力。 惯性力促使流体继续运动, 因而导致不稳定。 粘滞力阻抗外力干扰, 因而流体会成为层流。 在比较粘稠的液体如蜂蜜, 粘滞力几乎每次都赢。 不太粘稠的物质比如水或空气 更易被惯性力控制,
We measure where a flow falls on that spectrum with something called the Reynolds number, which is the ratio between a flow’s inertia and its viscosity. The higher the Reynolds number, the more likely it is that turbulence will occur. Honey being poured into a cup, for example, has a Reynolds number of about 1. The same set up with water has a Reynolds number that’s closer to 10,000.
由于不稳定而形成乱流。 我们测量流场流动情况, 用的单位是雷诺数, 是流体的惯性力与黏滞力比值。 雷诺数越大, 乱流出现的几率就越高。 比如,当蜂蜜被倒进杯子里, 雷诺数大约为一。
The Reynolds number is useful for understanding simple scenarios, but it’s ineffective in many situations. For example, the motion of the atmosphere is significantly influenced by factors including gravity and the earth’s rotation. Or take relatively simple things like the drag on buildings and cars. We can model those thanks to many experiments and empirical evidence. But physicists want to be able to predict them through physical laws and equations as well as we can model the orbits of planets or electromagnetic fields.
如果把蜂蜜换成水, 雷诺数就接近一万。 雷诺数对理解简单的场景有用, 但它在许多情况下会无效。 例如,大气层的运动 会被重力和地球的自转等因素所影响。 或者相对简单的例子, 比如建筑物和汽车上的阻力。 我们可以依据很多 实验和实践证据建模, 但物理学家们希望能够 通过物理定律和方程式来预测, 就如同我们可以构建 星球轨道或极场模型。
Most scientists think that getting there will rely on statistics and increased computing power. Extremely high-speed computer simulations of turbulent flows could help us identify patterns that could lead to a theory that organizes and unifies predictions across different situations. Other scientists think that the phenomenon is so complex that such a full-fledged theory isn’t ever going to be possible.
大多数科学家认为要达到 那个目标要依赖统计学 以及更强的运算能力。 超高速计算机对乱流的模拟 可能会帮助我们找到规律并形成理论, 并能够整合统一针对不同情况的预测。 其他的科学家觉得这个现象太过复杂, 这样一个完善的理论永远不可能。
Hopefully we’ll reach a breakthrough, because a true understanding of turbulence could have huge positive impacts. That would include more efficient wind farms; the ability to better prepare for catastrophic weather events; or even the power to manipulate hurricanes away. And, of course, smoother rides for millions of airline passengers.
希望我们能够取得突破, 因为对乱流的真正理解 可能会产生巨大的影响。 包括更加高效的风力发电, 更好的预知灾难性天气的能力, 甚至是操纵飓风的力量。 当然还会给数百万航空公司的乘客 更平稳的旅途。