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Aeroacoustic investigation of diaphragm orifices in ducts
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.ORCID iD: 0000-0001-7898-8643
2007 (English)In: Turkish Acoustical Society - 36th International Congress and Exhibition on Noise Control Engineering, INTER-NOISE 2007 ISTANBUL, 2007, 292-301 p.Conference paper, Published paper (Refereed)
Abstract [en]

Diaphragm orifices are used in duct systems to control or measure the flow rate. Such components generate complex flows and aeroacoustic phenomena, e.g., dissipation via forced vortex shedding, sound generation from eddy structures (broadband noise) and non-linear whistling. In this paper the acoustic properties (passive and active) of single and double diaphragm orifices are investigated experimentally for small Mach-numbers and low frequencies (plane waves). Using microphone arrays and wave decomposition the induct sound fields are resolved and used as input to determine the active acoustic 2-port. The work represents one of the first efforts to apply 2-port methods to characterize flow generated noise in-ducts. The motivation of this work is to obtain better understanding for noise from flow singularities in ducts, e.g., in HVAC systems on vehicles, develop and improve prediction methods and produce data for validation of CFD and other models. First the single orifice case is investigated and the 2-port data is obtained. The active (source) strength part represents a dipole type of source for which a scaling law is derived. For the passive part (the scattering matrix) a simple quasi-stationary model is tested and works well up to a few hundred Hz. Secondly the double orifice configuration is investigated and again the 2-port data is measured. To investigate the presence of orifice interaction and non-linear aeroacoustic effects, such as whistling, the double orifice data is reduced to two identical single orifices. The equivalent source data for this reduced case is then compared with the single orifice scaling law. It is found that if the separation is larger than 10 orifice diameters then orifice interaction can be neglected. Non-linear effects and tendencies for whistling were found for separations less than 3-4 duct diameters.

Place, publisher, year, edition, pages
2007. 292-301 p.
Keyword [en]
Acoustic fields, Acoustic properties, Aeroacoustics, Air conditioning ducts, Climate control, Diaphragms, Exhibitions, Flow rate, Orifices, Scattering parameters
National Category
Vehicle Engineering
Identifiers
URN: urn:nbn:se:kth:diva-154628Scopus ID: 2-s2.0-84873978021ISBN: 978-160560385-8 (print)OAI: oai:DiVA.org:kth-154628DiVA: diva2:759069
Conference
36th International Congress and Exhibition on Noise Control Engineering, INTER-NOISE 2007, 28 August 2007 through 31 August 2007, Istanbul, Turkey
Note

QC 20141028

Available from: 2014-10-29 Created: 2014-10-27 Last updated: 2014-10-29Bibliographically approved

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Åbom, Mats

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