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The role of shear-layer instability waves in jet exhaust noise

Published online by Cambridge University Press:  11 April 2006

C. J. Moore
C. J. Moore
Affiliation:
Advanced Research Laboratories, Rolls-Royce Limited, P.O. Box 31, Derby, England
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Abstract

Large-scale structures in the form of instability waves are an inherent part of a shearlayer mixing process. Such structures are shown to be present in an acoustically and aerodynamically well behaved jet even at high Mach numbers. They do not directly radiate significant acoustic power in a subsonic jet, but do govern the production of the turbulent fluctuations which radiate broad-band jet noise. Over the whole subsonic Mach number range, a significant increase in jet noise can be produced by exciting the shear layer with a fluctuating pressure at the nozzle of only 0·08 % of the jet dynamic head but with the correct Strouhal number. Such excitation by internal acoustic, aerodynamic or thermal fluctuations could explain the variability of jet noise measurements between different rigs and could also be responsible for some components of ‘excess’ noise.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 80 , Issue 2 , 25 April 1977 , pp. 321 - 367
Copyright
© 1977 Cambridge University Press

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