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Acoustic characterization of orifices and perforated liners with flow and high-level acoustic excitation
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Flow acoustics.ORCID iD: 0000-0002-0900-6391
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is motivated by the need for noise control in aircraft engine with orifices and perforated liner. The presence of high-level acoustic excitation, different flow situations either bias flow, grazing flow or any combination in the aircraft engine, makes the acoustic behavior complex due to the interaction between sound and flow over the lined wall. Both systematic acoustic prediction of aircraft engines and liner optimization necessitate progress in impedance measurement methods by including the effect of the complex flow situations. The aim of the present thesis is to experimentally study the change in acoustic properties of orifices and perforated liners under bias or grazing flow.

In order to study the effect of different combinations of bias flow and high-level acoustic excitation, an in-duct orifice has been investigated with finely controlled acoustic excitation levels and bias flow speeds. This provides a detailed study of the transition from cases when high-level acoustic excitation causes flow reversal in the orifice to cases when the bias flow maintains the flow direction. Nonlinear impedance is measured and compared, and a scattering matrix and its eigenvalues are investigated to study the potentiality of acoustic energy dissipation or production. A harmonic method is proposed for modelling the impedance, especially the resistance, which captures the change in impedance results at low frequencies compared with experimental results.

The presence of grazing flow can increase the resistance of acoustic liners and shift their resonator frequency. So-called impedance eduction technology has been widely studied during the past decades, but with a limited confidence due to the interaction of grazing flow and acoustic waves. A comparison has been performed with different test rigs and methods from the German Aerospace Center (DLR). Numerical work has been performed to investigate the effect of shear flow and viscosity. Our study indicates that the impedance eduction process should be consistent with that of the code of wave propagation computation, for example with the same assumption regarding shear flow and viscosity. A systematic analysis for measurement uncertainties is proposed in order to understand the essentials for data quality assessment and model validation. The idea of using different Mach numbers for wave dispersion and in the Ingard-Myers boundary condition has been tested regarding their effect on impedance eduction. In conclusion, a local Mach number based on friction velocity is introduced and validated using both our own experimental results and those of previous studies.  

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , vi, 61 p.
Series
TRITA-AVE, ISSN 1651-7660 ; 2015:26
Keyword [en]
Bias Flow, Grazing Flow, Nonlinear Acoustics, Acoustic Impedance, Impedance Eduction, Single Mode Straightforward Method, Uncertainty Analysis, LEE, LNSE
National Category
Applied Mechanics
Research subject
Järnvägsgruppen - Ljud och vibrationer
Identifiers
URN: urn:nbn:se:kth:diva-167114ISBN: 978-91-7595-614-5 (print)OAI: oai:DiVA.org:kth-167114DiVA: diva2:813073
Public defence
2015-06-09, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 12:42 (English)
Opponent
Supervisors
Note

QC 20150522

Available from: 2015-05-22 Created: 2015-05-21 Last updated: 2015-05-22Bibliographically approved
List of papers
1. Experimental investigation of an in-duct orifice with bias flow under medium and high level acoustic excitation
Open this publication in new window or tab >>Experimental investigation of an in-duct orifice with bias flow under medium and high level acoustic excitation
2014 (English)In: International Journal of Spray and Combustion Dynamics, ISSN 1756-8277, Vol. 6, no 3, 267-292 p.Article in journal (Refereed) Published
Abstract [en]

This paper experimentally investigates the acoustic properties of an orifice with bias flow under medium and high sound level excitation. Orifices with two different edge configurations were tested. The study includes a wide range of bias flow velocities, various acoustic excitation levels and different frequencies. The nonlinear acoustic scattering matrix was identified by a finely controled two-source method. Aeroacoustic modal analysis was introduced based on eigenvalue-decomposition. Acoustic properties, such as impedance, nonlinear scattering matrix and the eigenvalues were compared and discussed. Experimental results also show that bias flow makes the acoustic properties more complex compared to the no bias flow case, especially when the velocity ratio between acoustic particle velocity and mean flow velocity is near unity.

Place, publisher, year, edition, pages
Multi-Science Publishing, 2014
Keyword
Acoustic impedance, Acoustic properties, Acoustic wave transmission, Eigenvalues and eigenfunctions, Flow velocity, Modal analysis, Orifices, Scattering parameters, Velocity Acoustic excitation, Acoustic particle velocity, Different frequency, Experimental investigations, Mean flow velocities, Non-linear acoustics, Nonlinear scattering, Velocity ratio
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-128454 (URN)10.1260/1756-8277.6.3.267 (DOI)000342262900004 ()2-s2.0-84907447220 (Scopus ID)
Note

QC 20141028. Updated from submitted to published.

Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2015-05-22Bibliographically approved
2. The effect of combined high level acoustic excitation and bias flow on the acoustic properties of an in-duct orifice (AIAA 2013-2128)
Open this publication in new window or tab >>The effect of combined high level acoustic excitation and bias flow on the acoustic properties of an in-duct orifice (AIAA 2013-2128)
2013 (English)In: 19th AIAA/CEAS Aeroacoustics Conference, American Institute of Aeronautics and Astronautics, 2013, 1-13 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper investigates the acoustic properties of an orifice with bias flow under medium and high sound level excitation. Orifices with two different edge configurations were tested experimentally.The study includes a wide range of bias flow velocities, various acoustic excitation levels and different frequencies. The so-called Cummings equation was the starting point for the theoretical modelling. It was modified and a novel orifce acoustic discharge coefficient model was developed both for cases with and without bias flow. The model was experimentally validated. With this model the acoustic resistance is obtained by the harmonic balance method, and the results agree fairly well with the experimental results for low frequencies. Experimental results also show that bias flow makes the acoustic properties much more complex compared to the no bias flow case, especially when the velocity ratio between acoustic particle velocity and mean flow velocity is near unity.  

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2013
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-128456 (URN)10.2514/6.2013-2128 (DOI)2-s2.0-84883703222 (Scopus ID)
Conference
19th AIAA/CEAS Aeroacoustics Conference, 27-29 May, 2013, Berlin, Germany
Note

QC 20131016

Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2015-05-22Bibliographically approved
3. Comparison of impedance eduction results using different methods and test rigs
Open this publication in new window or tab >>Comparison of impedance eduction results using different methods and test rigs
Show others...
2014 (English)In: 20th AIAA/CEAS Aeroacoustics Conference, 2014Conference paper, Published paper (Refereed)
Abstract [en]

The last twenty years has seen a large development in inverse techniques for the determination of liner impedance under grazing flow conditions, so called impedance eduction techniques. This paper contribute to a continuing effort to gain confidence in results obtained using different test rigs as well as different impedance eduction techniques. The latter includes the use of different equations for solving for the sound field in the lined section. The DLR reference liner sample HR-S2 studied is a locally reacting single degree of freedom Helmholtz resonator liner which has previously been tested at DLR and NASA Langley. In this study it is tested in a smaller scale facility at KTH, but under similar mean flow and sound pressure level conditions as in the previous studies. A good agreement has been obtained for different method under the same plug flow assumption. The same trend but not identical effects of nonlinearity have been obtained with high levels of acoustic excitation. The effect of different flow Mach number assumptions are discussed in connection with the use of the Ingard-Myers boundary condition.

Keyword
Acoustic fields, Aeroacoustics, NASA, Acoustic excitation, Grazing flows, Helmholtz resonators, Impedance eduction, Inverse techniques, Liner impedance, Single degree of freedoms, Sound pressure level, Acoustic wave transmission
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-167356 (URN)10.2514/6.2014-2955 (DOI)2-s2.0-84903906546 (Scopus ID)9781624102851 (ISBN)
Conference
20th AIAA/CEAS Aeroacoustics Conference, 2014 Atlanta, USA
Note

QC 20150522

Available from: 2015-05-22 Created: 2015-05-22 Last updated: 2016-12-05Bibliographically approved
4. Effect of viscosity on impedance eduction and validation
Open this publication in new window or tab >>Effect of viscosity on impedance eduction and validation
(English)Manuscript (preprint) (Other academic)
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-167358 (URN)
Note

QS 2015

Available from: 2015-05-22 Created: 2015-05-22 Last updated: 2015-05-22Bibliographically approved
5. A systematic uncertainty analysis for liner impedance eduction technology
Open this publication in new window or tab >>A systematic uncertainty analysis for liner impedance eduction technology
2015 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 356, 86-99 p., 12557Article in journal (Refereed) Published
Abstract [en]

Abstract The so-called impedance eduction technology is widely used for obtaining acoustic properties of liners used in aircraft engines. The measurement uncertainties for this technology are still not well understood though it is essential for data quality assessment and model validation. A systematic framework based on multivariate analysis is presented in this paper to provide 95 percent confidence interval uncertainty estimates in the process of impedance eduction. The analysis is made using a single mode straightforward method based on transmission coefficients involving the classic Ingard-Myers boundary condition. The multivariate technique makes it possible to obtain an uncertainty analysis for the possibly correlated real and imaginary parts of the complex quantities. The results show that the errors in impedance results at low frequency mainly depend on the variability of transmission coefficients, while the mean Mach number accuracy is the most important source of error at high frequencies. The effect of Mach numbers used in the wave dispersion equation and in the Ingard-Myers boundary condition has been separated for comparison of the outcome of impedance eduction. A local Mach number based on friction velocity is suggested as a way to reduce the inconsistencies found when estimating impedance using upstream and downstream acoustic excitation.

National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-167359 (URN)10.1016/j.jsv.2015.07.001 (DOI)2-s2.0-84938745518 (Scopus ID)
Note

Updated from manuscript to article.

QC 20151021

Available from: 2015-05-22 Created: 2015-05-22 Last updated: 2017-12-04Bibliographically approved

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