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Absorption of sound at a surface exposed to flow and temperature gradients
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Scania CV AB, Sweden.ORCID iD: 0000-0003-1604-8263
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.ORCID iD: 0000-0003-4103-0129
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. Scania CV AB, Sweden.ORCID iD: 0000-0002-3826-3055
2016 (English)In: Applied Acoustics, ISSN 0003-682x, Vol. 110, 33-42 p.Article in journal (Other academic) Published
Abstract [en]

In noise abatement using porous or fibrous materials, accurate determination of the surface impedance representing the absorber is decisive for simulation quality. The presence of grazing flow and non-homogeneous ambient temperature influence the reaction of the absorber and may suitably be included in a modified “effective” surface impedance. In this paper, this approach is applied to a generic case representative for the engine bay of a heavy truck, where porous shields suppress the radiated noise, e.g. during a pass-by noise test. The change in the absorption is determined numerically by solving the wave propagation through a layer of varying temperature and flow adjacent to the impedance surface for different angles of incidence. The study shows significant impact of both flow and temperature, especially for materials with low absorption. The diffuse field absorption coefficient is also derived and although the effect is less pronounced in this case, it is still important in lower frequencies and in the frequency range typical for IC engine noise. The proposed numerical method is shown to be accurate and efficient for determination of the effective impedance and moreover not limited to thin boundary layers.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 110, 33-42 p.
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-183440DOI: 10.1016/j.apacoust.2016.03.017ISI: 000377232500005OAI: oai:DiVA.org:kth-183440DiVA: diva2:911091
Note

QC 20160407

Available from: 2016-03-11 Created: 2016-03-11 Last updated: 2016-06-28Bibliographically 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.
Series
TRITA-AVE, ISSN 1651-7660 ; 2016:09
Keyword
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
Identifiers
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)
Opponent
Supervisors
Note

QC 20160311

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

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