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Studies of sound generation and propagation in flow ducts
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
2006 (English)Licentiate thesis, monograph (Other scientific)
Abstract [en]

This thesis contains three papers investigating problems of interest for noise control in ducts.

The first part of this thesis treats the sound propagation in rectangular ducts with flexible walls. Various experimental techniques are performed to measure the internal sound propagation and radiation to the surrounding. An analytical model is derived to calculate the coupled propagation wavenumber and radiated sound power. The two-port formalism is used.

The second part starts with the sound propagation in open ended circular straight pipe with airflow (a tailpipe). Various aspects such as: acoustic damping, reflection and transmission at the open termination are investigated. Sound absorption due to vorticity shed at the opening is also treated. The geometry of the opening is then modified (oblique cuts, diffusers) and comparisons with the reference straight pipe is made for the sound transmission and flow induced noise generation. The effect of an upstream bend close to the opening is also investigated.

In the third part the acoustic impedance of perforated plates are investigated. In particular the application to small perforation ratios ( ≈ 1% ) and holes or slits with apertures of sub-millimetre size, so called micro-perforated plates, are of interest. Linear and non-linear regimes are investigated. A model is derived to calculate the linear acoustic impedance of perforated elements.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , 260 p.
Trita-AVE, ISSN 1651-7660 ; 2006:34
Keyword [en]
two-port, plane wave, HVAC system, tailpipe, exhaust system, flexible duct, pipe, reflection coefficient, impedance, flow noise, vorticity, damping, scaling laws, impedance, transmission loss, perforated plate, slit, non linearity
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:kth:diva-4049OAI: diva2:10549
2006-06-16, MWL 74, Teknikringen 8, KTH, SE 100 44 Stockholm, 10:00
QC 20101111Available from: 2006-06-13 Created: 2006-06-13 Last updated: 2010-11-11Bibliographically approved

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