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Linear and nonlinear mechanisms of sound radiation by instability waves in subsonic jets

Published online by Cambridge University Press:  30 June 2010

VICTORIA SUPONITSKY ,
NEIL D. SANDHAM  and
CHRISTOPHER L. MORFEY
VICTORIA SUPONITSKY*
Affiliation:
School of Engineering Sciences, University of Southampton, Southampton SO17 1BJ, UK
NEIL D. SANDHAM
Affiliation:
School of Engineering Sciences, University of Southampton, Southampton SO17 1BJ, UK
CHRISTOPHER L. MORFEY
Affiliation:
ISVR, University of Southampton, Southampton SO17 1BJ, UK
*
†Email address for correspondence: [email protected]
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Abstract

Linear and nonlinear mechanisms of sound generation in subsonic jets are investigated by numerical simulations of the compressible Navier–Stokes equations. The main goal is to demonstrate that low-frequency waves resulting from nonlinear interaction between primary, highly amplified, instability waves can be efficient sound radiators in subsonic jets. The current approach allows linear, weakly nonlinear and highly nonlinear mechanisms to be distinguished. It is demonstrated that low-frequency waves resulting from nonlinear interaction are more efficient in radiating sound when compared to linear instability waves radiating directly at the same frequencies. The results show that low-frequency sound radiated predominantly in the downstream direction and characterized by a broadband spectral peak near St = 0.2 can be observed in the simulations and described in terms of the nonlinear interaction model. It is also shown that coherent low-frequency sound radiated at higher angles to the jet axis (θ = 60°–707°) is likely to come from the interaction between two helical modes with azimuthal wavenumbers n = ±1. High-frequency noise in both downstream and side-line directions seems to originate from the breakdown of the jet into smaller structures.

JFM classification

Acoustics: Aeroacoustics Acoustics: Jet noise Instability: Nonlinear instability
Type
Papers
Information
Journal of Fluid Mechanics , Volume 658 , 10 September 2010 , pp. 509 - 538
Copyright
Copyright © Cambridge University Press 2010

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