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Acoustic modes in a duct with slowly varying impedance and non-uniform mean flow and temperature
KTH, School of Engineering Sciences (SCI), Mechanics, Turbulence.
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2011 (English)In: 17th AIAA/CEAS Aeroacoustics Conference 2011 (32nd AIAA Aeroacoustics Conference), 2011Conference paper (Refereed)
Abstract [en]

Noise from the auxiliary power unit (APU) is becoming an increasingly important aircraft design constraint because of the noise exposure during ground operations ("ramp-noise"). Reduction of noise may be achieved by liners in the exhaust duct. In this paper, we will consider the propagation of sound through the APU exhaust duct, which is typically straight with an axially varying liner depth, a non-uniform mean flow and strong temperature gradients. We present a solution in the form of slowly varying modes of WKB type for the acoustic pressure field inside a duct with an impedance that is continuously varying in the axial direction. In cross-wise direction each WKB mode is given by eigenfunction-type solutions of the Pridmore-Brown equation. A new numerical approach based on a standard implementation of a collocation method supplemented by a path-following procedure is presented to solve this equation. We compare the results of the slowly-varying solution with a solution based on mode-matching between axial segments with constant impedance.

Place, publisher, year, edition, pages
Keyword [en]
Acoustic pressure field, Aircraft design, Auxiliary power units, Axial direction, Collocation method, Non-uniform mean flow, Numerical approaches, Propagation of sounds, Aeroacoustics, Auxiliary power systems, Ducts, Eigenvalues and eigenfunctions, Ground operations, Noise pollution, Numerical methods, Acoustic noise
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:kth:diva-148681ScopusID: 2-s2.0-84883104325ISBN: 9781600869433OAI: diva2:749920
17th AIAA/CEAS Aeroacoustics Conference 2011 (32nd AIAA Aeroacoustics Conference), 5 June 2011 through 8 June 2011, Portland, OR, United States

QC 20140925

Available from: 2014-09-25 Created: 2014-08-11 Last updated: 2014-09-25Bibliographically approved

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Lazeroms, Werner M. J.
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