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The Effect of Boundary Layers on Bulk Reacting Liners at Low Mach Number Flows
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.ORCID iD: 0000-0003-1604-8263
KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.ORCID iD: 0000-0003-4103-0129
2013 (English)Conference paper, Published paper (Other academic)
Abstract [en]

Sound absorbing linings are effective noise treatments in many applications in order to meet noise emission requirements. Stricter noise requirements set harder demands on the performance of the liners, why better prediction models of their performance have to be developed. As of today, several models to predict the sound reducing properties in the presence of flow exist and are shown to give diverging absorption properties for locally reacting liners exposed to high Mach number flows. The effect of flow on absorption properties is often seen as an issue that only needs to be addressed at high Mach number flows. In this paper, the existing models are applied to bulk reacting liners exposed to low Mach number flows and the resulting absorption coefficients are compared. Predictions of absorption coefficients clearly show that the effect of flow needs to be considered also at low Mach number flows and that the difference between the prediction models is indeed significant at low Mach number flows. This shows the importance in choosing the correct model for a specific application in order to avoid introducing erroneous prediction on the effect of flow. This study thus gives well-grounded evidence of the importance to include flow effects in modeling of sound absorptive linings even at low Mach number flows.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2013.
Keyword [en]
Sound absorption, surface impedance, grazing flow, liners
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-128559Scopus ID: 2-s2.0-84883681935OAI: oai:DiVA.org:kth-128559DiVA: diva2:648084
Conference
19th AIAA/CEAS Aeroacoustics Conference, 27-29 May, 2013, Berlin, Germany
Note

QC 20130913

Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2016-11-25Bibliographically approved
In thesis
1. Analysis of Acoustic Absorption with Extended Liner Reaction and Grazing Flow
Open this publication in new window or tab >>Analysis of Acoustic Absorption with Extended Liner Reaction and Grazing Flow
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Acoustic absorbing liners are efficient and commonly used measures to reduce sound levels in many fields of application. The sound reducingperformance of the liners is dependent on the acoustic state, defined by e.g. the flow and sound field interacting with the liner. To enable liner optimization the impact of these factors on the liner performance must be predictable. Studies of the impact of these factors were performed with existing experimental, analytical and numerical methods at low Mach number flows and material used in truck engine compartments. The study showed significant impact of both flow and sound field onthe liner performance. The size of the impact of the flow depends on which of the existing methods and models that was used, implying theneed of complementary methods. A new numerical method to model the boundary layer effect was for this reason developed in this work. The method was shown to predict the impact of flow correctly compared to the Pridmore-Brown solution and the method was computationally efficient. The sound reducing performance of a liner exposed to complex sound field and grazing flow can be predicted using existing methods together with the new proposed method. Extra care has to be taken when bulk reacting liners are considered since additional complications compared to locally reacting surfaces occur in presence the of grazing flow.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. x, 46 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2013:42
Keyword
Sound absorption, acoustic lining, non-locally reacting, boundary layer, grazing flow, sound field, transfer matrix method
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-128711 (URN)
Presentation
2013-09-27, K2, Teknikringen 28, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20130916

Available from: 2013-09-16 Created: 2013-09-16 Last updated: 2013-09-16Bibliographically approved

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