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Attenuation of sound in a low Mach Number nozzle flow

Published online by Cambridge University Press:  19 April 2006

M. S. Howe
M. S. Howe
Affiliation:
Bolt, Beranek & Newman Inc., 50 Moulton Street, Cambridge, Massachusetts 02138
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Abstract

This paper examines the energy conversion mechanisms which govern the emission of low frequency sound from an axisymmetric jet pipe of arbitrary nozzle contraction ratio in the case of low Mach number nozzle flow. The incident acoustic energy which escapes from the nozzle is partitioned between two distinct disturbances in the exterior fluid. The first of these is the free-space radiation, whose directivity is equivalent to that produced by monopole and dipole sources. Second, essentially incompressible vortex waves are excited by the shedding of vorticity from the nozzle lip, and may be associated with the large-scale instabilities of the jet. Two linearized theoretical models are discussed. One of these is an exact linear theory in which the boundary of the jet is treated as an unstable vortex sheet. The second assumes that the finite width of the mean shear layer of the real jet cannot be neglected. The analytical results are shown to compare favourably with recent attenuation measurements.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 91 , Issue 2 , 23 March 1979 , pp. 209 - 229
Copyright
© 1979 Cambridge University Press

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