Improving Noise Reduction in Airbus Engine Nacelles

AI Thread Summary
The discussion focuses on advancements in noise reduction technology for Airbus engine nacelles, particularly the introduction of a zero splice liner that eliminates seams, which are typically sources of resonance. These liners act as acoustic barriers, especially around fan tips, improving sound quality by reducing transmission of noise rather than focusing it. The design challenges of creating a single-piece liner with proper composite properties are acknowledged as significant achievements. While the overall noise remains, the nature of the sound is improved, making it less intrusive. The conversation highlights the importance of understanding engine noise dynamics, particularly fan tip and exhaust gas noise.
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This may be of interest to readers:
http://www.flightglobal.com/articles/2007/01/23/211641/airbus-a350-xwb-set-to-be-quietest-generation-of-airliner-as-manufacturer-improves-zero-splice.htm

A noise reduction engine nacelle intake. "A zero splice liner with a continuous surface and lacking the distinct joins that exist on conventional liners."

How do liners reduce the noise and why is this one an improvement?
 
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Liners are accoustic barriers. Especially around fan tips where there are usually some pretty complicated aerodynamic things happening. The whole idea of the single piece is that the seams, no matter how tight you make them, are sources for resonance and transmission. It is very impressive that they figured out a way to do it in a single piece. That is no easy task and to have the composite properties come out properly.
 
So does the noise get focused in one direction instead of spreading out when a liner is used? And is the liner of uniform thickness or thicker where the engine noise is greatest? Do the noisiest places in the engine occur at different locations as engine speed changes?
 
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The noise doesn't really get focused. It just isn't impeded. Of course, the nature of the noise is dependent on the conditions and frequencies. It depends highly on the engine. The two big hitters on most engines, is fan tip pass (fan noise) and exhaust gas noise. Exhaust noise was effected greatly by the invention of the turbo fan that reduced exhaust temperatures and velocities. Our engines can have a pretty decent whine to them under certain conditions because of the fan tips. Other components do contribute but not as much as the two stated.
 
FRED GARVIN said:
"The noise doesn't really get focused. It just isn't impeded"

So there's just as much noise but it makes a nicer sound?
 

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