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On the noise sources of the unsuppressed high-speed jet

Published online by Cambridge University Press:  29 March 2006

K. A. Bishop ,
J. E. Ffowcs Williams  and
W. Smith
K. A. Bishop
Affiliation:
Rolls-Royce Ltd, Bristol Engine Division
J. E. Ffowcs Williams
Affiliation:
Rolls-Royce Ltd, Bristol Engine Division
W. Smith
Affiliation:
Rolls-Royce Ltd, Bristol Engine Division
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Abstract

The paper describes an interpretation of jet-noise theory and scale-model experiments to highlight physical properties of jet-noise sources at very high speed. The study is prompted by current efforts to suppress the noise of supersonic transport aircraft.

The principal noise sources are shown to be very large-scale wave-like undulations of the jet flow that travel downstream at supersonic speed for a distance of several jet diameters. These motions are relatively well ordered and are probably more akin to recognizable instabilities of a laminar flow than the confused small-scale turbulence. Because of this we postulate a model of the noise generating motions as the instability products of a jet flow of low equivalent Reynolds number. This Reynolds number is based on an eddy viscosity and can be further reduced by artificially increasing the small-scale turbulence level. This step would tend to stabilize the flow and inhibit the formation of large-scale noise producing eddies.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 50 , Issue 1 , 15 November 1971 , pp. 21 - 31
Copyright
© 1971 Cambridge University Press

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