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On the noise of a nearly ideally expanded supersonic jet

Published online by Cambridge University Press:  29 March 2006

Christopher K. W. Tam
Christopher K. W. Tam
Affiliation:
Department of Aeronautics and Astronautics, Massachusetts Institute of Technology Present address: Department of Mathematics, Florida State University.
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Abstract

A noise generation mechanism for a nearly ideally expanded supersonic jet is proposed. It is suggested that the dominant part of the noise of a supersonic jet is generated at two rather localized regions of the jet. These regions are located at distances quite far downstream of the nozzle exit. Large-scale instabilities of the jet flow are believed to be responsible for transferring the kinetic energy of the jet into noise radiation. An analysis based on a simple mathematical model reveals that two large-scale unstable waves are preferentially amplified in a supersonic jet. The rapid growth of these waves causes the oscillations of the jet to penetrate the mixing layer at two locations and to interact strongly with the ambient fluid there. This gives rise to intense noise radiation. Theoretical results based on the proposed noise generation mechanism are found to compare favourably with experimental measurements. A simple scaling formula is also derived.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 51 , Issue 1 , 11 January 1972 , pp. 69 - 95
Copyright
© 1972 Cambridge University Press

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