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Aeroacoustic Characterization using Multiport Methods
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Noise is a major environmental pollutant, which can inict physical and psychologicalinjury. An important noise contribution stems from aeroacousticsources, which are found in e.g., ventilation ducts, engine exhaust systems andairplane engines.In this thesis, research methods for low Mach number aeroacoustic sourcesin ducts are developed. The basis of the methods is the ability to describe theintrinsic linear properties of the source as an N-port (multiport), where theoutput sound eld is related to the input sound eld and the generated soundeld, all consisting of plane waves. The methods presented are both numericaland experimental. The numerical method treats the passive properties, i.e.,scattering, attenuation and amplication of incident sound, while the experimentalmethod treats the active part (intrinsic sound generation) as well. Themethods are applied in the study of noise generation by a vortex mixer plate,placed in an airow of Mach 0.2, and in the study of acoustic-hydrodynamicinteraction in a T-junction of rectangular ducts.It is found that the accuracy of the experimental methods is signicantly increasedwhen the equations are over-determined, which is achieved by addingadditional microphones to the test rig. In the frequency range studied, themixer plate is found to generate less sound when made exible, without disturbingthe mixing quality.For the numerical method { based on the linearized Navier-Stokes equations,a model of the oscillation of the Reynolds stress (\turbulent damping")due to the acoustic eld is introduced. By comparing with experimental results,it is found that not using this model results in an over-prediction of theamplication at higher frequencies with several factors in magnitude, whileimplementing the model results in a much better agreement.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , vi, 66 p.
Series
Trita-AVE, ISSN 1651-7660 ; 2012:76
Keyword [en]
Aeroacoustics, Multiport, Experiments, Computational Aeroacoustics, Mixer Plate, T-junction.
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-105396ISBN: 978-91-7501-563-7 (print)OAI: oai:DiVA.org:kth-105396DiVA: diva2:571621
Public defence
2012-12-10, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilTrenOp, Transport Research Environment with Novel Perspectives
Note

QC 20121123

Available from: 2012-11-23 Created: 2012-11-20 Last updated: 2013-04-11Bibliographically approved
List of papers
1. Experimental determination of the aero-acoustic properties of an in-duct flexible plate
Open this publication in new window or tab >>Experimental determination of the aero-acoustic properties of an in-duct flexible plate
Show others...
2008 (English)In: 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), 2008Conference paper, Published paper (Refereed)
Abstract [en]

The potential reduction of the aeroacoustic noise generated by an in duct plate, byallowing it to be flexible, is studied experimentally. The test object is a triangular plateinserted at an angle in a circular flow duct. Results are given for the active and passiveacoustic properties. In addition the flow field and the vibrations of the plate arecharacterized. It is found that an appropriately yielding plate reduces the flow generatednoise while keeping the mean flow field unaffected.

Keyword
Aeroacoustic noise, Circular flow, Experimental determination, Flexible plates, Flow-generated noise, Mean flow fields, Potential reduction, Test object, Triangular plates
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-26135 (URN)2-s2.0-78249257017 (Scopus ID)9781563479397 (ISBN)
Conference
14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference); Vancouver, BC; Canada; 5 May 2008 through 7 May 2008
Note

QC 20101118

Available from: 2010-11-16 Created: 2010-11-16 Last updated: 2014-10-13Bibliographically approved
2. Accurate experimental two-port analysis of flow generated sound
Open this publication in new window or tab >>Accurate experimental two-port analysis of flow generated sound
2011 (English)In: Sound & vibration, ISSN 1541-0161, Vol. 330, no 26, 6336-6354 p.Article in journal (Other academic) Published
Abstract [en]

In the study of in-duct aero-acoustic phenomena two-port analysis based upon in-duct measurements has become an important method for the plane wave region. However already at moderate Mach numbers (0.2 - 0.3) the errors in the results can be hard to suppress. Ways of dealing with this includes the use of over-determination methods and methods of obtaining more accurate wave numbers. In this paper different methods for the determination of the source data and the scattering matrix are evaluated. For the source data in the form of a cross spectrum matrix an over-determination method is introduced. In addition, a method of obtaining the mean Mach number from experimentally determined wave numbers is described.

In order to evaluate the methods measurements are conducted at a mean Mach number of 0.2 for two test cases – an empty duct and a mixer plate inside the duct. The main improvements in the scattering matrix results are achieved by discarding measurements from an abundant set, based upon the measured coherence between excitation and fluctuating pressures. For the source part, it is shown that the error in the magnitude of the source cross spectrum matrix can be significantly suppressed by having additional (> 2) reference microphones on each side of the two-port.

The mean Mach number obtained from an experimentally determined wave number is observed to yield more accurate scattering matrix results in both phase and magnitude, than that based upon flow velocity measurements at one point and an assumed flow profile.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-26137 (URN)10.1016/j.jsv.2011.07.041 (DOI)000296403600004 ()2-s2.0-80053254335 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20101118. Uppdaterad från Manuskript till Artikel (20111121) Available from: 2010-11-16 Created: 2010-11-16 Last updated: 2017-12-12Bibliographically approved
3. Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows: an experimental investigation
Open this publication in new window or tab >>Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows: an experimental investigation
(English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568Article in journal (Other academic) Submitted
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-105697 (URN)
Note

QS 2012

Available from: 2012-11-23 Created: 2012-11-23 Last updated: 2017-12-07Bibliographically approved
4. A Linearized Navier-Stokes Method Including Turbulence Damping
Open this publication in new window or tab >>A Linearized Navier-Stokes Method Including Turbulence Damping
(English)Article in journal (Other academic) Submitted
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-105700 (URN)
Note

QS 2012

Available from: 2012-11-23 Created: 2012-11-23 Last updated: 2012-11-23Bibliographically approved

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