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An Extended Transfer Matrix Approach to Model the Effect of Boundary Layers on Acoustic Linings
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.ORCID iD: 0000-0003-1604-8263
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.ORCID iD: 0000-0003-4103-0129
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Sound absorbing materials exposed to grazing flow experience a change in the surface properties due to the boundary layer developed above the surface. The effect of this boundary layer is significant even for fairly low Mach numbers, and several attempts to find analytical models to describe this effect have previously been made. This paper proposes a numerical discretization method, based on the classic transfer matrix approach to model the boundary layer effect. The method includes the time averaged flow velocity gradients of the boundary layer, which is shown to be essential in order to obtain convergence to the correct solution. The method is found to predict the effect of the boundary layer on the surface properties correctly compared to previous numerical solutions. The proposed method is simple to implement, and benets from a fast convergence relative to other numerical methods.

Keyword [en]
grazing flow, surface impedance, sound absorption
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:kth:diva-128560OAI: diva2:648095


Available from: 2013-09-13 Created: 2013-09-13 Last updated: 2013-09-16Bibliographically 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.
Trita-AVE, ISSN 1651-7660 ; 2013:42
Sound absorption, acoustic lining, non-locally reacting, boundary layer, grazing flow, sound field, transfer matrix method
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-128711 (URN)
2013-09-27, K2, Teknikringen 28, KTH, Stockholm, 13:00 (English)

QC 20130916

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

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