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This question already has an answer here:

I've noticed that there are saw-teeth on modern jet engines such as the GEnx and the Rolls Royce Trent 1000. What is their purpose?

Lufthansa Kisses Chevrons

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marked as duplicate by fooot, reirab, Federico, CGCampbell, Ralph J May 17 '15 at 21:28

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ You mean on the back? $\endgroup$ – raptortech97 May 17 '15 at 18:59
  • $\begingroup$ @fooot, the question that is said to be similar, is addressing a more specific issue. $\endgroup$ – Madhav Sudarshan May 17 '15 at 19:51
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    $\begingroup$ Can you edit the question to explain how this one is less specific? Right now they are both just asking "what is their purpose," and the answers are very similar. $\endgroup$ – fooot May 17 '15 at 19:57
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These "saw-teeth" or "chevrons" or even "acoustic liners", are there to help reduce noise generated from the operation of the engine.

As hot air from the inner core of the engine mixes with the other, cooler air, it generates noise. These "saw-teeth" are there to help smooth that mixing, thereby generating less noise which is the result of turbulence. These are seen on the Boeing 747-8 (as seen in your picture) and the Boeing 787.

The reduction of sound generated means that less noise insulation is needed for use in the fuselage of the airplane. Less insulation means less weight. Less-weight equals less fuel burn, which means that chevrons are great for passengers, and economics.

There's only one difference from your picture. As much as we would like them to blow kisses to everyone, that's not what they are there for. :)

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    $\begingroup$ Thank you so much @Zizouz212, the answer was very informative and helpful. $\endgroup$ – Madhav Sudarshan May 17 '15 at 19:53
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To quote from the Wikipedia article on the subject:

In aerospace industry, chevrons are the sawtooth patterns on the trailing edges of some jet engine nozzles[1] that are used for noise reduction. Their principle of operation is that, as hot air from the engine core mixes with cooler air blowing through the engine fan, the shaped edges serve to smooth the mixing, which reduces noise-creating turbulence.[1] Chevrons were developed with the help of NASA.[1][2] Some notable examples of such engines include GEnx and Rolls-Royce Trent 1000.

  1. Banke, Jim (2012-12-13). "NASA Helps Create a More Silent Night". NASA. Retrieved January 12, 2013.
  2. Zaman, K.B.M.Q.; Bridges, J. E.; Huff, D. L. (17–21 December 2010). "Evolution from 'Tabs' to 'Chevron Technology’–a Review" (PDF-1.34 MB). Proceedings of the 13th Asian Congress of Fluid Mechanics 17–21 December 2010, Dhaka, Bangladesh (NASA Glenn Research Center. Cleveland, Ohio). Retrieved January 29, 2013.
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    $\begingroup$ Please link to the article, don't just quote it and paste the citations as if this was your own content. $\endgroup$ – egid May 17 '15 at 23:45
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    $\begingroup$ @egid If its a quote, it isn't my own content is it? Link only answers are discouraged. Also, pasting saves the trouble of going to the link. Also, in some cases the relevant text is buried on the page, so I am extracting the relevant part of the page. $\endgroup$ – Tyler Durden May 17 '15 at 23:53
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    $\begingroup$ I think it's safe to say that quote-only answers are also discouraged, but maybe we should start a meta thread about it. Alternately, maybe answers like these should be community wikis. Either way — what if someone wanted to read more? There's no reason to put a fair bit of effort into including the citations and then not drop in the link to the article. $\endgroup$ – egid May 17 '15 at 23:55
  • $\begingroup$ And, in this case, you actually pasted the entire article $\endgroup$ – egid May 18 '15 at 0:45
  • $\begingroup$ @egid Normally I would never do a copy and paste answer, but in this case the wiki completely answers the question. The question in fact in a lot of forums would not be allowed because it is trivially answered by the wikipedia. $\endgroup$ – Tyler Durden May 18 '15 at 1:00

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