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Jet noise shielding: Mean flow convection and refraction effects on jet noise source propagation
Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland.ORCID iD: 0000-0003-0176-5358
Trinity College Dublin, Department of Mechanical and Manufacturing Engineering, Ireland.
2008 (English)In: 23rd International Conference on Noise and Vibration Engineering, ISMA, Leuven University Press, 2008, 525-533 p.Conference paper (Other academic)
Abstract [en]

Positioning aircraft engines on the rear of the fuselage above a U-shaped empennage, is an aircraft configuration, which could possibly reduce the engine noise emitted towards the ground during take-off and approach. In order to acoustically assess the shielding effect attained from such a configuration, the complicated physical noise sources must, firstly, be represented in a manner appropriate for input into propagation / shielding prediction methods. In this paper, the development of an innovative methodology for providing such a source for jet noise is described. Convecting point sources are located using Lighthill's analogy with a Reynolds-Averaged Navier Stokes (RANS) solution to provide mean flow properties. The refractive effect of the mean jet flow on sound propagation is determined using a Wave Expansion Method (WEM) to efficiently numerically propagate monopole noise sources in a small domain, which includes the sheared jet flow. This near-field WEM result is then propagated to the far-field using the Helmholtz-Kirchhoff integral equation, assuming a uniform flow external to the Kirchhoff surface. The refractive flow effect on omnidirectional sources is superimposed on the convecting sources. These directional point sources may be used as a sound source input for shielding prediction methods. In this present study, jet noise sources have been created for a range of frequencies. The isolated sound pressure level and the shielding effect, resultant from separating these sources from an arc of receivers, with a flat plate, have been evaluated and results compared with test data. Results presented here are very encouraging, as they clearly indicate that with the inclusion of both the convective and the refractive effects of the jet flow on the propagation of point sources, simple jet noise sources may be defined for use in shielding prediction methods, however, using the present approximations, the predicted sound pressure levels are greater than the measured values at downstream receiver angles.

Place, publisher, year, edition, pages
Leuven University Press, 2008. 525-533 p.
Keyword [en]
Acoustic noise measurement, Acoustic wave transmission, Aircraft engines, Empennages, Fire alarm systems, Forecasting, Fuselages, Navier Stokes equations, Shielding, Aircraft configurations, Innovative methodologies, Mean flow properties, Physical noise sources, Prediction methods, Refraction effects, Reynolds-averaged navier stokes, Sound pressure level
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:kth:diva-159527ISI: 000263409900038ScopusID: 2-s2.0-84906355064ISBN: 978-90-73802-86-5OAI: diva2:785472
23rd International Conference on Noise and Vibration Engineering 2008, ISMA 2008, Leuven, Belgium, 15 September 2008 through 17 September 2008

QC 20150204

Available from: 2015-02-03 Created: 2015-02-03 Last updated: 2016-08-22Bibliographically approved

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