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Originally Posted by freebeard
kach22i -- ???
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I was addressing Otto's question based on the assumption he and others had knowledge of the now commonly used noise reduction used on jets.
News, Current Space updates, Rockets,Constellation,Satellites,Space Research,: space shuttle orbiter
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A jet engine noise reduction device called a chevron, now in use on commercial airliners, is a good example of a NASA-developed technology that climbed the TRL scale to success, said Fay Collier, manager of NASA's Environmentally Responsible Aviation Project.
Chevrons are the saw-tooth pattern that can be seen on the trailing edges of some jet engine nozzles. As hot air from the engine core mixes with cooler air blowing through the engine fan, the jagged edges serve to smooth the mixing, which reduces turbulence that creates noise.
The new Boeing 787 is among the most modern jets relying on chevrons to reduce engine noise levels, sporting chevrons on the nacelles, or fan housings. The Boeing 747-8 has chevrons on both the nacelles and inner core engine nozzles.
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the jagged edges serve to smooth the mixing, which reduces turbulence that creates noise.
What that description fails to explain is that varying distances expand the noise energy over a wider spectrum (via traveling distance) thereby taking the loudest peak down. It is after-all our hearing perception which indicates loudness by the highest frequency peak within our hearing spectrum.
Otto was imaging wheel pants or wheel fairings with a saw-tooth (serrated edge) pattern.
The only advantage I know of is because of sound (or cutting).
http://weaponsedge.com/how-to-sharpen-a-knife/
Question answered?
In nature there is the bat wing. Has more to do with bone structure and tensioned membranes than aerodynamic advantages I believe.
http://krisallegra.blogspot.com/2012...g-helping.html
If the bat's wing shape cuts down on sound so that it can silently hunt insects, then all the better I guess.
On a car, tire and engine sound is going to heavily outweigh aerodynamic sound in my opinion.