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On internal mean flow in porous absorbers and its effect on attenuation properties
Centre for ECO Vehicle Design, Scania CV, Södertälje, Sweden.ORCID iD: 0000-0003-1604-8263
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.ORCID iD: 0000-0003-4103-0129
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Numerical acoustics.ORCID iD: 0000-0003-1855-5437
Scania CV, Södertälje, Sweden.ORCID iD: 0000-0002-3826-3055
2013 (English)In: Proceedings of Meetings on Acoustics: Volume 19, 2013, Acoustical Society of America (ASA), 2013, Vol. 19, 1-6 p.Conference paper (Other academic)
Abstract [en]

In vehicle applications, absorbing materials are often used to attenuate sound. In, for example, exhaust systems and on noise encapsulations, the absorber is exposed to flow. This creates a boundary layer above the absorber, which affects the impedance of the surface, and hence alters the absorption properties. In addition to this effect, the flow itself may enter the absorbent material due to high pressure and forced flow paths. An investigation of the effects that internal flow in the absorber imposes on the acoustic properties is presented. One way to describe the effect is by a change in flow resistivity. The effect is investigated for typical absorbers used in noise encapsulations for trucks. The Transfer Matrix Method is applied to calculate the resulting absorption coefficient for an absorber with changed flow resistivity due to internal flow. The possibility to model the changed properties of the absorber with internal mean flow by means of Biot theory is also explored, together with a discussion on suitable experimental methods to verify and further investigate the effects.

Place, publisher, year, edition, pages
Acoustical Society of America (ASA), 2013. Vol. 19, 1-6 p.
, Proceedings of Meetings on Acoustics, ISSN 1939-800X ; 19
Keyword [en]
Absorbent materials, Absorbing materials, Absorption co-efficient, Absorption property, Attenuation properties, Experimental methods, Flow resistivity, In-vehicle applications
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-134241DOI: 10.1121/1.4799717ScopusID: 2-s2.0-84878976617OAI: diva2:665855
21st International Congress on Acoustics, ICA 2013 - 165th Meeting of the Acoustical Society of America; Montreal, QC; Canada; 2 June 2013 through 7 June 2013

QC 20131121. QC 20160129. QC 20160207

Available from: 2013-11-21 Created: 2013-11-20 Last updated: 2016-03-11Bibliographically approved
In thesis
1. Absorption of Sound: On the effects of field interaction on absorber performance
Open this publication in new window or tab >>Absorption of Sound: On the effects of field interaction on absorber performance
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Environmental noise has for decades been a well known problem, especially in urban areas. As noise requirements for vehicles are sharpened, noise reducing concepts are needed in early design stages requiring accurate simulations to support the design. Specifically for optimization of noise treatments, the absorber performance must be simulated correctly.

So called noise encapsulations are placed below the powertrain on heavy vehicles to enclose the engine and reduce noise radiation. The attenuation of the absorbers on these shields must be represented correctly in simulations, even in environments with complex sound field, cooling flow and high temperature variations which may affect the absorber performance. This thesis studies the performance variation due to different absorber representations and due to these factors and how to include this in simulations.

It is shown that the material representation significantly affects the attenuation performance in the simulations. Assuming locally reacting absorbers neglects the full interaction between the sound field and the material, which was shown to affect the noise reduction considerably. A measurement method to determine the angular dependent surface impedance was evaluated. It was shown sensitive to small samples and a method to improve accuracy was suggested. Including the angular dependence, either by full resolution or an angular dependent impedance, the field-absorber interaction is included in the simulations and more accurate results are obtained. The influence of flow and temperature fields on the absorber performance was also investigated. A method to include these effects was developed and the attenuation performance shown significant, especially for materials with bulk reaction.

In conclusion, thorough knowledge of the material behavior and the field in the applications is required to choose appropriate material representation to enable reliable simulation results.​


Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 45 p.
TRITA-AVE, ISSN 1651-7660 ; 2016:09
Sound absorption, Porous absorbers, Bulk reaction, Local reaction, Boundary layer, Grazing flow, Temperature gradients, Surface impedance, Sound field, Pass-by noise
National Category
Fluid Mechanics and Acoustics
Research subject
Vehicle and Maritime Engineering
urn:nbn:se:kth:diva-183413 (URN)978-91-7595-883-5 (ISBN)
Public defence
2016-04-08, F3, Lindstedtsvägen 26, KTH, Stockholm, 09:00 (English)

QC 20160311

Available from: 2016-03-11 Created: 2016-03-10 Last updated: 2016-03-11Bibliographically approved

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