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Directivity of acoustic emissions from wave packets to the far field

Published online by Cambridge University Press:  10 November 2009

DOMINIK OBRIST
DOMINIK OBRIST*
Affiliation:
Institute of Fluid Dynamics, ETH Zurich, 8092 Zurich, Switzerland
*
†Email address for correspondence: obrist@ifd.mavt.ethz.ch
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Abstract

We investigate the acoustic emission from wave packets to the far field. To this end, we develop a theory for one- and two-dimensional source fields in the shape of wave packets with Gaussian envelopes. This theory is based on an approximation to Lighthill's acoustic analogy for distant observers. It is formulated in the spectral domain in which a Gaussian wave packet is represented again by a Gaussian. This allows us to determine the directivity of the acoustic emission (e.g. superdirectivity and Mach waves) by simple geometric constructions in the spectral domain. It is shown that the character of the acoustic emission is mainly governed by the aspect ratio and the Mach number of the wave packet source. To illustrate the relevance of this theory we use it to study two prominent problems in subsonic jet aeroacoustics.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 640 , 10 December 2009 , pp. 165 - 186
Copyright
Copyright © Cambridge University Press 2009

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