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New Type of Tip Jet to Reduce Noise

Published online by Cambridge University Press:  26 October 2023

E J Richards
E J Richards*
Affiliation:
University of Southampton, Department of Aeronautical Engineering
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Extract

During the past few years, it has become recognised that one of the major objections to the introduction of helicopters fitted with pressure jets at the blade tips is the high level of noise set up by the jets The source of this noise lies m the jet stream itself When air travelling at high speed mixes with the surrounding air, turbulence is formed in the region of high velocity shear and noise is emitted into the stationary or near stationary medium surrounding the jet The large velocity gradient or shear actually amplifies the sound (Ref 1) which increases as a very high power of the jet velocity, normally about the eighth power Needless to say, if turbulence exists initially in the jet stream, either from poor internal shaping of the engine or from incomplete burning of the fuel, the noise will be aggravated and a different noise law achieved With well designed jet umts, however, the eighth power law is obeyed surprisingly well

Type
Research Article
Information
The Journal of the Helicopter Association of Great Britain , Volume 9 , Issue 3 , January 1956 , pp. 404 - 413
Copyright
Copyright © Royal Aeronautical Society 1956

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Footnotes

*

This Paper was submitted by the Author as a written contribution for the Journal and is printed with the permission of the University of Southampton

References

Lighthill, M J On Sound Generated Aerodynamically—I General Theory, Proc Roy Soc A, Vol 211, pp 564-587, 195210.1098/rspa.1952.0060CrossRefGoogle Scholar
Richards, E J Problems of Noise in Helicopter Design Journ Helicopter Assn of Great Britain July, 1955Google Scholar
Ingard, U Review of the Influence of Meteorological Conditions on Sound Propagation Journ Acoustical Soc of America, Vol 25, No 3, May, 195310.1121/1.1907055CrossRefGoogle Scholar
Richards, E J and Evans, D J A New Concept in the Design of Jet Engine Mufflers and Sound Cells University of Southampton report to be publishedGoogle Scholar
Franklin, R E Noise Measurements on a Series of Convergent­Divergent Nozzles University of Southampton report to be publishedGoogle Scholar
Richards, E J and Jones, J P The Application of the Jet Flap to Helicopter Rotors Journ Helicopter Assn of Great Britain Vol 9 No 3Google Scholar