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Measurement of perforate impedance with grazing flow on both sides
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
2016 (English)In: 22nd AIAA/CEAS Aeroacoustics Conference. American Institute of Aeronautics and Astronautics., American Institute of Aeronautics and Astronautics, 2016Conference paper (Refereed)
Abstract [en]

In this paper, the acoustic impedance of a microperforated plate (MPP) with two-sided grazing flow is educed by a modified semi-analytical inverse technique. The MPP sample is placed in the middle of a rectangular duct with grazing flow. The mode matching formulation is derived in terms of pressure for a MPP with two-sided grazing flow. The inputs to this mode matching technique are complex acoustic pressure measured at twelve positions at the wall of the duct, upstream and downstream of the MPP section. First the ability of the code to reproduce the pressure field for a given impedance is tested. Second the ability to educe the correct impedance for a given pressure distribution is tested. The results of the mode matching code are in good agreement with the simulations for no flow cases.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2016.
National Category
Mechanical Engineering Aerospace Engineering
URN: urn:nbn:se:kth:diva-192866DOI: 10.2514/6.2016-2853ScopusID: 2-s2.0-84982962151OAI: diva2:972578
AIAA/CEAS Aeroacoustics Conference
EU, FP7, Seventh Framework Programme, 289352

QC 20160927

Available from: 2016-09-21 Created: 2016-09-21 Last updated: 2016-09-27Bibliographically approved
In thesis
1. Innovative noise control in ducts
Open this publication in new window or tab >>Innovative noise control in ducts
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of this doctoral thesis is to study three different innovative noise control techniques in ducts namely: acoustic metamaterials, porous absorbers and microperforates. There has been a lot of research done on all these three topics in the context of duct acoustics. This research will assess the potential of the acoustic metamaterial technique and compare to the use of conventional methods using microperforated plates and/or porous materials. 

The objective of the metamaterials part is to develop a physical approach to model and synthesize bulk moduli and densities to feasibly control the wave propagation pattern, creating quiet zones in the targeted fluid domain. This is achieved using an array of locally resonant metallic patches. In addition to this, a novel thin slow sound material is also proposed in the acoustic metamaterial part of this thesis. This slow sound material is a quasi-labyrinthine structure flush mounted to a duct, comprising of coplanar quarter wavelength resonators that aims to slow the speed of sound at selective resonance frequencies. A good agreement between theoretical analysis and experimental measurements is demonstrated.

The second technique is based on acoustic porous foam and it is about modeling and characterization of a novel porous metallic foam absorber inside ducts. This material proved to be a similar or better sound absorber compared to the conventional porous absorbers, but with robust and less degradable properties. Material characterization of this porous absorber from a simple transfer matrix measurement is proposed.The last part of this research is focused on impedance of perforates with grazing flow on both sides. Modeling of the double sided grazing flow impedance is done using a modified version of an inverse semi-analytical technique. A minimization scheme is used to find the liner impedance value in the complex plane to match the calculated sound field to the measured one at the microphone positions.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 69 p.
TRITA-AVE, ISSN 1651-7660 ; 58
Locally resonant materials, slow sound, acoustic impedance, metallic foam, low frequency noise, mufflers, lined ducts, grazing flow, flow duct, impedance eduction.
National Category
Vehicle Engineering
Research subject
Vehicle and Maritime Engineering
urn:nbn:se:kth:diva-192927 (URN)978-91-7729-119-0 (ISBN)
Public defence
2016-10-21, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
EU, FP7, Seventh Framework Programme, 289352

QC 20160923

Available from: 2016-09-23 Created: 2016-09-23 Last updated: 2016-09-23Bibliographically approved

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