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Acoustic Nacelles

Published on 02/08/2013 08:30 - By

It’s well known that the sound of aircraft overhead is sometimes deafening ! Without acoustic treatment, the noise generated by the engines would be unbearable to the human ear.

At Aircelle, specialists in the manufacture of commercial aircraft nacelles, such as for the A380 seen here, they have not turned a deaf ear to this problem; on the contrary, they treat the noisiest areas of jet engines.

Marc Versaevel, Engineering Acoustics - Aircelle (Safran Group):

"The fan which is very large, is one of the primary sources to treat in the engine; so, to do that, we put an acoustic lining in the air intake, as you can see on this A380 nacelle, the black liner of the nacelle starts here, and goes back as far as the fan. To treat the fan noise, which normally spreads through the thrust reverser, we have another acoustic treatment as seen here in the by-pass duct.’’

And to contain the noise, and resist the temperature extremes which may range from -60 ° C at the inlet to +700 ° C at the outlet or tail end, various materials such as carbon, aluminum and titanium are used.

Marc Versaevel, Engineering Acoustics - Aircelle (Safran Group):

"We use a sandwich structure composed of acoustic absorbent materials: a perforated skin on the internal fan side, a porous internal structure using a honey-combed interior with foam cells, and then the outer acoustic reflecting skin."

For example, on an A380 engine nacelle, some 10 million holes are provided in an area of 40 m2 ( 430 sq.ft ). An engine that does not emit any noise is a dream for people living near airports, but may not be as unrealistic as that. Aircelle has has already initiated research work with academics and acoustic experts on the subject, and hope to find the answer to this problem within the next ten years.

Denis Jontef, Program Manager Research and Technology - Aircelle (Safran Group):

"How can these technologies, technologies that exist in stereo headsets for example, be used in things that can be integrated into nacelles, and allow us to measure the noise source, its shape if you prefer, and interact with it ? The principle is that the acoustic wave can be offset by what is very technically called, phase-shifted wavelength, to 90 °, so as to cancel out the residual amplitude."

Meanwhile, Aircelle are working on an intermediate solution: to increase the acoustic surface of a nacelle by adding this type of material in strategic locations; nevertheless over the last 20 years progress in this area has been enormous! And as proof of this, the acoustics of the nacelles have a lot to do with the fact that the four engines of the massive A380 emit an equivalent reduced noise level to that of two A320 engines!

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