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Simulations of the scattering of sound waves at a sudden area expansion
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0003-4103-0129
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0002-9061-4174
2012 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 331, no 5, 1068-1083 p.Article in journal (Refereed) Published
Abstract [en]

The scattering of acoustic plane waves at a sudden area expansion in a flow duct is simulated using the linearized Navier-Stokes equations. The aim is to validate the numerical methodology for the flow duct area expansion, and to investigate the influence of the downstream mean flow on the acoustic scattering properties. A comparison of results from numerical simulations, analytical theory and experiments is presented. It is shown that the results for the acoustic scattering obtained by the different methods gives excellent agreement. For the end correction, the numerical approach is found superior to the analytical model at frequencies where coupling of acoustic and hydrodynamic waves is significant. A study with two additional flow profiles, representing a non-expanding jet with infinitely thin shear layer, and an immediate expansion, shows that a realistic jet is needed to accurately capture the acoustic-hydrodynamic interaction. A study with several different artificial jet expansions concluded that the acoustic scattering is not significantly dependent on the mean flow profile below the area expansion. The constructed flow profiles give reasonable results although the reflection and transmission coefficients are underestimated, and this deviation seems to be rather independent of frequency for the parameter regime studied. The prediction of the end correction for the constructed mean flow profiles deviates significantly from that for the realistic profile in a Strouhal number regime representing strong coupling between acousticand hydrodynamic waves. It is concluded that the constructed flow profiles lack the ability to predict the loss of energy to hydrodynamic waves, and that this effect increases with increasing Mach number.

Place, publisher, year, edition, pages
Elsevier, 2012. Vol. 331, no 5, 1068-1083 p.
Keyword [en]
aeroacoustics, frequency-domain, linearized Navier-Stokes, scattering, duct
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-33774DOI: 10.1016/j.jsv.2011.09.011ISI: 000299459100008Scopus ID: 2-s2.0-82955247818OAI: oai:DiVA.org:kth-33774DiVA: diva2:417481
Funder
TrenOp, Transport Research Environment with Novel PerspectivesSwedish e‐Science Research Center
Note

QC 20120309

Available from: 2011-05-17 Created: 2011-05-17 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Frequency Domain Linearized Navier-Stokes Equations Methods for Low Mach Number Internal Aeroacoustics
Open this publication in new window or tab >>Frequency Domain Linearized Navier-Stokes Equations Methods for Low Mach Number Internal Aeroacoustics
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Traffic is a major source of environmental noise in modern day's society. As a result, the development of new vehicles are subject to heavy governmental legislations. The major noise sources on common road vehicles are engine noise, transmission noise, tire noise and, at high speeds, wind noise. One way to reduce intake and exhaust noise is to attach mufflers to the exhaust pipes. However, to develop prototypes for the evaluation of muffler performance is a costly and time-consuming process. As a consequence, in recent years so called virtual prototyping has emerged as an alternative. Current industrial simulation methodologies are often rather crude, normally only including one-dimensional mean flows and one-dimensional acoustic fields. Also, flow generated noise is rudimentary modeled or not included at all. Hence, improved methods are needed to fully benefit from the possibilities of virtual prototyping.

This thesis is aimed at the development of simulation methodologies suitable both as industrial tools for the prediction of the acoustic performance of flow duct systems, as well as for analyzing the governing mechanisms of duct aeroacoustics. Special focus has been at investigating the possibilities to use frequency-domain linearized Navier-Stokes equations solvers, where the equations are solved either directly or as eigenvalue formulations.

A frequency-domain linearized Navier-Stokes equations methodology has been developed to simulate sound propagation and acoustic scattering in flow duct systems. The performance of the method has been validated to experimental data and analytical solutions for several cases of in-duct area expansions and orifice plates at different flow speeds. Good agreement has generally been found, suggesting that the proposed methodology is suitable for analyzing internal aeroacoustics.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. vii, 78 p.
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-33763 (URN)978-91-7501-008-3 (ISBN)
Public defence
2011-05-27, Sal E3, Osquars backe 14, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research CenterTrenOp, Transport Research Environment with Novel Perspectives
Note
QC 20110517Available from: 2011-05-17 Created: 2011-05-16 Last updated: 2012-06-12Bibliographically approved

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Boij, SusannEfraimsson, Gunilla

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