The earliest recorded evidence of this can be seen over a thousand years ago in Persia.

最早的記錄證據可以在一千多年前的波斯看到。

But these machines have evolved from simple devices used to crush grain and pump water.

但是，這些機器已經從用於粉碎穀物和抽水的簡單設備發展而來。

To towering monsters generating enough electricity to power entire towns.

高聳入雲的怪獸產生的電力足以為整個城鎮供電。

Traditional wind turbines come in many shapes and designs.

傳統的風力渦輪機有多種形狀和設計。

But they have all given way to a fairly consistent three blade design.

但它們都讓位於相當一致的三葉設計。

Today we're going to answer the question, why do wind turbines have three blades?

今天我們要回答的問題是：為什麼風力渦輪機有三個葉片？

We can imagine each blade as a wrench tightening a nut.

我們可以把每一把刀想象成一把擰緊螺母的扳手。

If we increase the length of the wrench, we can generate more torque.

如果我們增加扳手的長度，就能產生更大的扭矩。

That's the force that causes rotation.

這就是導致旋轉的力。

Likewise, if we add a second wrench, we can apply even more force.

同樣，如果我們增加第二個扳手，就可以施加更大的力。

The same principle applies to wind turbines.

這一原則同樣適用於風力渦輪機。

So naturally, you may think, why not add as many blades and make them as long as possible?

是以，你可能會想，為什麼不增加刀片的數量，並使它們儘可能長呢？

The biggest wind turbine has a diameter of 164 m, each blade weighs 33 tons and each costs hundreds of thousands of dollars to manufacture.

最大的風力渦輪機直徑達 164 米，每個葉片重 33 噸，每個葉片的製造成本達數十萬美元。

So more blades equals more weight and more cost.

是以，葉片越多，重量越重，成本越高。

So maybe less blades is better?

也許刀片越少越好？

Let's compare our standard three blade design to its immediate competitors, a two blade turbine and a four blade turbine.

讓我們將我們的標準三葉片設計與其直接競爭對手--雙葉片渦輪機和四葉片渦輪機進行比較。

Let's assume they have the same blade design for now.

我們暫且假設它們的刀片設計相同。

We can easily eliminate the four blade design with a quick cost analysis, each of these blades cost a lot of money, adding a fourth blade provides such a marginal increase in performance that it does not justify the additional cost.

我們可以通過快速的成本分析輕鬆地取消四葉片設計，因為每個葉片的成本都很高，增加第四個葉片對性能的提升微乎其微，不足以證明額外成本的合理性。

So it's down to two and three blades.

現在只剩兩片和三片刀片了。

A two bladed design can match the performance of a three bladed design by increasing the chord of the blade by 50%.

將葉片的弦長增加 50%，雙葉片設計就能達到三葉片設計的性能。

Which eliminates the cost advantage, so it's pointless.

這就消除了成本優勢，是以毫無意義。

Or we can increase the rotational speed by 22.5%.

或者，我們可以將轉速提高 22.5%。

Turbines with two blades will spin faster in the same wind due to the reduced drag they experience.

有兩個葉片的渦輪機在風力相同的情況下會旋轉得更快，這是因為它們受到的阻力減少了。

But spinning faster is a negative.

但旋轉速度越快就越不利。

Let's explore why.

讓我們來探究一下原因。

A faster spinning blade will generate more noise.

轉速更快的刀片會產生更大的噪音。

This is what a wind turbine sounds like up close.

這就是風力渦輪機的近距離聲音。

Yeah, people don't like living next to these things.

是的，人們不喜歡住在這些東西旁邊。

So we need to minimize the noise they make by minimizing their speed.

是以，我們需要通過儘量降低它們的速度來減少噪音。

Next, we need to worry about centrifugal force, as the blades spin faster, their apparent weight increases, thus the central hub and the blades need to be stronger to resist the additional stress.

其次，我們需要擔心離心力，因為葉片旋轉得越快，其表面重量就越大，是以中心輪轂和葉片需要更加堅固，以抵抗額外的壓力。

Again, this adds cost.

這再次增加了成本。

This is what can happen when a wind turbine's brakes fail in strong winds.

這就是風力渦輪機的制動器在強風中失靈時可能發生的情況。

So a three blade design can generate more power at slower rotational speeds than a two blade design, while being more cost efficient than a four bladed option.

是以，與雙葉片設計相比，三葉片設計能以較慢的轉速產生更大的功率，同時又比四葉片設計更具成本效益。

So the three bladed design is our Goldilocks choice, not too much and not too little.

是以，三葉片設計是我們的黃金選擇，既不會太多，也不會太少。

Thanks for watching and happy Earth Day.

感謝您的收看，祝您地球日快樂。

Don't forget to subscribe and see my next video, which will explain the history and physics behind winglets, which are those curly bits at the end of wings.

別忘了訂閱並觀看我的下一個視頻，它將解釋小翼（機翼末端的捲曲部分）背後的歷史和物理學原理。