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Determination of in-duct sound power beyond the plane wave range using wall-mounted microphones
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).ORCID iD: 0000-0001-7898-8643
2015 (English)In: Applied Acoustics, ISSN 0003-682X, E-ISSN 1872-910X, Vol. 99, 24-30 p.Article in journal (Refereed) Published
Abstract [en]

When studying the acoustic wave propagation in a duct, the frequency range can be divided into the low frequency plane wave range and the high frequency range with non-plane waves. In the low frequency range, the wave propagation is one-dimensional and the governing equations are rather simple. The larger the duct, the lower the frequency limit of the non-plane waves. Therefore, also taking into account the three-dimensional acoustic wave propagation is important, especially when considering the duct systems used in large machines. In practice often a harsh environment and immobile structures restrict the use of standardized noise measuring methods. For instance to characterize the exhaust noise of medium speed internal combustion engines (IC-engines) in situ, the in-duct sound pressures are measured using wall-mounted microphones. Then the low frequency range source sound power can be estimated by wave decomposition ("two-microphone method"). Often a three-microphone array is used to cover a sufficiently large frequency range. One way to formulate the sound pressure and sound power relationship in the high frequency range is to weight the sound pressures at the duct wall in one-third octave bands. The aim of this study is to extend the classical plane wave formulation by determining these weighting factors, so that a three-microphone array also can be used beyond the plane wave range. The results from numerical approach are compared to experimental data.

Place, publisher, year, edition, pages
2015. Vol. 99, 24-30 p.
Keyword [en]
Exhaust noise, IC-engine, In-duct, Non-plane waves, Sound power
National Category
Other Engineering and Technologies
URN: urn:nbn:se:kth:diva-170221DOI: 10.1016/j.apacoust.2015.05.003ISI: 000358969200003ScopusID: 2-s2.0-84930958691OAI: diva2:828453

QC 20150630

Available from: 2015-06-30 Created: 2015-06-29 Last updated: 2015-12-14Bibliographically approved
In thesis
1. Acoustic In-duct Characterization of Fluid Machines with Applications to Medium Speed IC-engines
Open this publication in new window or tab >>Acoustic In-duct Characterization of Fluid Machines with Applications to Medium Speed IC-engines
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The unwanted sound, noise, can lead to health problems, e.g. hearing loss and stress-related problems. A pre-knowledge of noise generation by machines is of great importance due to the ever-shorter product development cycles and stricter noise legislation. The noise from a machine radiates to the environment indirectly via the foundation structure and directly via the surrounding fluid. A fluid machine converts the energy from the fluid into mechanical energy or vice versa. Examples of the fluid machines are internal combustion engines (IC-engines), pumps, compressors, and fans. Predicting and controlling noise from a fluid machine requires a model of the noise sources themselves, i.e. acoustic source data. In the duct systems connected to the fluid machines, the acoustic source interacts strongly with the system boundaries, and the source characteristics must be described using in-duct methods.

Above a certain frequency, i.e. first non-plane wave mode cut-on frequency, the sound pressure varies over the duct cross-section and non-plane waves are introduced. For a number of applications, the plane wave range dominates and the non-plane waves can be neglected. But for machines connected to large ducts, the non-plane wave range is also important. In the plane wave range, one-dimensional process simulation software can be used to predict, e.g. for IC-engines, the acoustic in-duct source characteristics. The high frequency phenomena with non-plane waves are so complicated, however, that it is practically impossible to simulate them accurately. Thus, in order to develop methods to estimate the sound produced, experimental studies are also essential.

This thesis investigates the acoustic in-duct source characterization of fluid machines with applications to exhaust noise from medium speed IC-engines.  This corresponds to large engines used for power plants or on ships, for which the non-plane wave range also becomes important. The plane wave source characterization methods are extended into the higher frequency range with non-plane waves. In addition, methods to determine non-plane wave range damping for typical elements in exhaust systems, e.g. after-treatment devices, are discussed.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xi, 63 p.
TRITA-AVE, ISSN 1651-7660 ; 2015:86
in-duct, acoustic source, source characterization, IC-engine
National Category
Fluid Mechanics and Acoustics
urn:nbn:se:kth:diva-177341 (URN)978-91-7595-765-4 (ISBN)
Public defence
2015-12-10, sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)

QC 20151119

Available from: 2015-11-19 Created: 2015-11-18 Last updated: 2015-12-14Bibliographically approved

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Hynninen, AnttiÅbom, Mats
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