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Acoustic waves in ducts with thin shear layers
Växjö University, International Centre of Mathematical Modelling School of Mathematics and Systems Engineering, Sweden.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.ORCID iD: 0000-0003-4103-0129
2007 (English)In: 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 2007Conference paper (Refereed)
Abstract [en]

The acoustic properties of a duct may change radically if a mean flow is introduced. The reflection coefficient may for instance reach a peak greater than one at an abrupt open pipe termination and at sudden area expansions the reflection properties may have a strong Strouhal number dependence. Simulations of these phenomena using a model of an issuing jet with a constant cross-section coupling to the slower or quiescent medium by a vortex layer have compared favourably with experiments. Stability of the flow should have a central role in this flow-acoustic interaction. To investigate the importance of stability for the scattering of sound at edges this paper deals with the study of waves in a duct where the flow is not necessary unstable. An accompanying paper treats the scattering of sound at edges in the duct. The flow-acoustic coupling is modelled with a newly proposed set of coupling conditions relating the fields on both sides of an acoustically thin shear layer. The model is uniform in the Strouhal number s based on the shear layer thickness at the exit. For vanishing s the model agrees with the unstable vortex layer model, the layer is stable for s larger than a transfer Strouhal number and the model reduces to the quiescent case for infinite s. In addition to continuity of sound pressure we use continuity for a quantity, being displacement for vanishing s, velocity for s equals the transfer Strouhal number and pressure gradient for infinite s. The stabilizing mechanism reduces for increasing s the acoustic transverse length scale compared to the corresponding scale for the mean flow. The current paper deals with motivating and using the new coupling conditions to study the waves in a duct. The main purpose is to investigate the properties of the acoustic and hydrodynamic waves as well as their interaction. Of interest is also to verify the required stability properties of the model.

Place, publisher, year, edition, pages
Keyword [en]
Acoustic fields, Acoustic properties, Aeroacoustics, Computer simulation, Ducts, Shear flow, Stability, Strouhal number, Vortex flow
National Category
Vehicle Engineering
URN: urn:nbn:se:kth:diva-154692ScopusID: 2-s2.0-84884795339ISBN: 978-162410003-1OAI: diva2:765714
13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 21 May 2007 through 23 May 2007, Rome, Italy

QC 20141124

QC 20160921

Available from: 2014-11-24 Created: 2014-10-27 Last updated: 2016-09-21Bibliographically approved

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Boij, Susann
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