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The generation of sound by two-phase nozzle flows and its relevance to excess noise of jet engines

Published online by Cambridge University Press:  29 March 2006

O. J. Whitfield  and
M. S. Howe
O. J. Whitfield
Affiliation:
Engineering Department, University of Cambridge Present address: Mechanical Engineering Laboratory, G.E.C. Power Engineering, Cambridge Road, Whetstone, Leicestershire.
M. S. Howe
Affiliation:
Engineering Department, University of Cambridge
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Abstract

This paper describes a prototype model experiment designed to test the principle that the ‘excess’ noise of a jet issuing from a conical nozzle can be significantly diminished by reducing the maximum pressure gradient in the flow. The experiment uses a water jet containing flow inhomogeneities in the form of air or helium bubbles exhausting through a conventional conical nozzle or a specially contoured ‘bellmouth’ nozzle. It is argued that the level of the internally generated noise is controlled by the mean-flow pressure gradient, and substantial reductions in the sound level are recorded with the bellmouth nozzle. Certain features of the acoustic pressure signatures of the two-phase flow are examined in detail, in particular a rather surprising absolute difference in the sound pressure levels produced when helium rather than air bubbles are used under otherwise identical mean-flow conditions. Theoretical arguments are advanced which appear to explain the principal features of the observations.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 75 , Issue 3 , 11 June 1976 , pp. 553 - 576
Copyright
© 1976 Cambridge University Press

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