Change search
ReferencesLink to record
Permanent link

Direct link
A systematic uncertainty analysis for liner impedance eduction technology
KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Marcus Wallenberg Laboratory MWL.ORCID iD: 0000-0002-8474-8563
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.

Place, publisher, year, edition, pages
2015. Vol. 356, 86-99 p., 12557
National Category
Fluid Mechanics and Acoustics
URN: urn:nbn:se:kth:diva-167359DOI: 10.1016/j.jsv.2015.07.001ScopusID: 2-s2.0-84938745518OAI: diva2:813239

Updated from manuscript to article.

QC 20151021

Available from: 2015-05-22 Created: 2015-05-22 Last updated: 2015-10-21Bibliographically approved
In thesis
1. Acoustic characterization of orifices and perforated liners with flow and high-level acoustic excitation
Open this publication in new window or tab >>Acoustic characterization of orifices and perforated liners with flow and high-level acoustic excitation
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.
TRITA-AVE, ISSN 1651-7660 ; 2015:26
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
urn:nbn:se:kth:diva-167114 (URN)978-91-7595-614-5 (ISBN)
Public defence
2015-06-09, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 12:42 (English)

QC 20150522

Available from: 2015-05-22 Created: 2015-05-21 Last updated: 2015-05-22Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Zhou, LinBodén, Hans
By organisation
Competence Center for Gas Exchange (CCGEx)Linné Flow Center, FLOWMarcus Wallenberg Laboratory MWL
In the same journal
Journal of Sound and Vibration
Fluid Mechanics and Acoustics

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 66 hits
ReferencesLink to record
Permanent link

Direct link