Turbulence: One of the great unsolved mysteries of physics - Tomás Chor

翻译人员: Yingyu Liu 校对人员: Lipeng Chen

You’re on an airplane when you feel a sudden jolt.

你在飞机上，

突然感到一阵颠簸。

Outside your window nothing seems to be happening,

你往窗外看外，

似乎什么都没有发生，

yet the plane continues to rattle you and your fellow passengers

可是持续的颠簸

让你和其他乘客感到不安，

as it passes through turbulent air in the atmosphere.

因为飞机正在通过大气中的乱流。

Although it may not comfort you to hear it,

虽然听起来不会让你欣慰，

this phenomenon is one of the prevailing mysteries of physics.

这个现象是依旧是 一个广为流传的物理谜团。

After more than a century of studying turbulence,

在对乱流进行了一个多世纪的研究后，

we’ve only come up with a few answers for how it works

我们只找到了几个解释，

and affects the world around us.

关于它的背后机理以及它对世界的影响。

And yet, turbulence is ubiquitous,

尽管如此，乱流无处不在，

springing up in virtually any system that has moving fluids.

几乎在任何流体系统中都会出现。

That includes the airflow in your respiratory tract.

包括你呼吸道里的气流，

The blood moving through your arteries.

你血管里流淌的血液，

And the coffee in your cup, as you stir it.

和你在搅拌的咖啡里。

Clouds are governed by turbulence,

云是被乱流支配的，同样的，

as are waves crashing along the shore and the gusts of plasma in our sun.

拍打着海岸的海浪以及 带离子体的太阳风也是。

Understanding precisely how this phenomenon works

如果能准确的理解这个原理，

would have a bearing on so many aspects of our lives.

会对我们生活的方方面面 产生很大的影响。

Here’s what we do know.

这些是我们目前所知道的。

Liquids and gases usually have two types of motion:

液体和气体一般会有两种动态：

a laminar flow, which is stable and smooth;

稳定平滑的称为层流，

and a turbulent flow, which is composed of seemingly unorganized swirls.

和看似无规律的漩涡 而组成的称为紊流。

Imagine an incense stick.

想象一炷熏香，

The laminar flow of unruffled smoke at the base is steady and easy to predict.

层流存在于烟雾基部， 稳定并且可预测。

Closer to the top, however,

可是越接近烟雾的上层

the smoke accelerates, becomes unstable,

由于烟雾加速， 变得非常不稳定，

and the pattern of movement changes to something chaotic.

运动模式也变的混乱。

That’s turbulence in action,

这就是乱流，

and turbulent flows have certain characteristics in common.

乱流有几个共同的特征。

Firstly, turbulence is always chaotic.

第一，乱流是混乱的。

That’s different from being random.

这与随机不同。

Rather, this means that turbulence is very sensitive to disruptions.

更准确来说，乱流对扰乱非常敏感。

A little nudge one way or the other

随意的轻轻一推

will eventually turn into completely different results.

就会导致完全不同的结果。

That makes it nearly impossible to predict what will happen,

这就导致几乎无法预测会发生什么，

even with a lot of information about the current state of a system.

即便有很多系统当前状态的信息。

Another important characteristic of turbulence

乱流的另一个重要的特征是

is the different scales of motion that these flows display.

表现出来的不同运动规模。

Turbulent flows have many differently-sized whirls called eddies,

乱流有很多不同大小的漩涡

名为涡流，

which are like vortices of different sizes and shapes.

它们像是不同大小的涡旋。

All those differently-sized eddies interact with each other,

这些不同大小的涡流互相影响，

breaking up to become smaller and smaller

变得越来越小，

until all that movement is transformed into heat,

直到这些动能转换成热能，

in a process called the “energy cascade."

这个过程叫做“能量串级”。

So that’s how we recognize turbulence–

这就是我们如何辨认乱流，

but why does it happen?

可是它为什么会发生呢？

In every flowing liquid or gas there are two opposing forces:

每一种流动液体或气体 都有两个相斥的力量：

inertia and viscosity.

惯性力与粘滞力。

Inertia is the tendency of fluids to keep moving,

惯性力促使流体继续运动，

which causes instability.

因而导致不稳定。

Viscosity works against disruption,

粘滞力阻抗外力干扰，

making the flow laminar instead.

因而流体会成为层流。

In thick fluids such as honey,

在比较粘稠的液体如蜂蜜，

viscosity almost always wins.

粘滞力几乎每次都赢。

Less viscous substances like water or air are more prone to inertia,

不太粘稠的物质比如水或空气 更易被惯性力控制，

which creates instabilities that develop into turbulence.

由于不稳定而形成乱流。

We measure where a flow falls on that spectrum

我们测量流场流动情况，

with something called the Reynolds number,

用的单位是雷诺数，

which is the ratio between a flow’s inertia and its viscosity.

是流体的惯性力与黏滞力比值。

The higher the Reynolds number,

雷诺数越大，

the more likely it is that turbulence will occur.

乱流出现的几率就越高。

Honey being poured into a cup, for example,

比如，当蜂蜜被倒进杯子里，

has a Reynolds number of about 1.

雷诺数大约为一。

The same set up with water has a Reynolds number that’s closer to 10,000.

如果把蜂蜜换成水， 雷诺数就接近一万。

The Reynolds number is useful for understanding simple scenarios,

雷诺数对理解简单的场景有用，

but it’s ineffective in many situations.

但它在许多情况下会无效。

For example, the motion of the atmosphere is significantly influenced

会被重力和地球的自转等因素所影响。

by factors including gravity and the earth’s rotation.

Or take relatively simple things like the drag on buildings and cars.

或者相对简单的例子， 比如建筑物和汽车上的阻力。

We can model those thanks to many experiments and empirical evidence.

我们可以依据很多 实验和实践证据建模，

But physicists want to be able to predict them through physical laws and equations

但物理学家们希望能够 通过物理定律和方程式来预测，

as well as we can model the orbits of planets or electromagnetic fields.

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

大多数科学家认为要达到 那个目标要依赖统计学

and increased computing power.

以及更强的运算能力。

Extremely high-speed computer simulations of turbulent flows

超高速计算机对乱流的模拟

could help us identify patterns that could lead to a theory

可能会帮助我们找到规律并形成理论，

that organizes and unifies predictions across different situations.

并能够整合统一针对不同情况的预测。

Other scientists think that the phenomenon is so complex

其他的科学家觉得这个现象太过复杂，

that such a full-fledged theory isn’t ever going to be possible.

这样一个完善的理论永远不可能。

Hopefully we’ll reach a breakthrough,

希望我们能够取得突破，

because a true understanding of turbulence could have huge positive impacts.

因为对乱流的真正理解 可能会产生巨大的影响。

That would include more efficient wind farms;

包括更加高效的风力发电，

the ability to better prepare for catastrophic weather events;

更好的预知灾难性天气的能力，

or even the power to manipulate hurricanes away.

甚至是操纵飓风的力量。

And, of course, smoother rides for millions of airline passengers.

当然还会给数百万航空公司的乘客 更平稳的旅途。