Optimum acoustic impedance in circular ducts with inviscid sheared flow: Application to turbofan engine intake

Spillere, Andre; Cordioli, Júlio A.

doi:10.1016/j.jsv.2018.12.007

Cited by 12 publications

(3 citation statements)

References 32 publications

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“…However, under suitable conditions, Cremer's impedance can lead to a reasonable approximation of the optimal impedance when compared to results obtained in more detailed numerical models of the turbofan engine duct using optimization routines. 19 In order to find Cremer's impedance, the derivative of equation ( 5) with respect to k r must vanish, 20 so…”

Section: In-situ Techniquementioning

confidence: 99%

Design of a single degree of freedom acoustic liner for a fan noise test rig

Spillere

Braga

Seki

et al. 2021

International Journal of Aeroacoustics

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Acoustic liners are an essential part of noise reduction technologies commonly applied in aircraft turbofan engines. Fan noise suppression can be achieved by selecting an appropriate liner design with optimal acoustic impedance at the blade passing frequency. Great efforts have been made not only to improve experimental characterization and numerical methods for acoustic liners, but also to understand noise generation mechanisms, which ultimately impacts on the liner design itself. To gain confidence in the liner design process, a liner barrel was developed and fabricated for the Fan Noise Test Rig located at the University of São Paulo. To this end, analytical methods were used to determine the optimal acoustic impedance for the Fan Noise Test Rig, and a flat test sample was fabricated for experimental characterization with flow using both in-situ and impedance eduction techniques at the Federal University of Santa Catarina. A liner barrel of same nominal geometry was fabricated and placed at the Fan Noise Test Rig, and a modal decomposition indicated that the Tyler-Sofrin mode has been successfully suppressed at the first blade passing frequency. Numerical predictions of liner transmission loss considering the flat sample impedance showed good agreement with experimental results.

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Section: In-situ Techniquementioning

confidence: 99%

Design of a single degree of freedom acoustic liner for a fan noise test rig

Spillere

Braga

Seki

et al. 2021

International Journal of Aeroacoustics

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show abstract

“…Recently, however, interest in the topic has burgeoned and a number of papers have appeared in the literature. Most of these research works deal with circular and annular ducts with flow and have potential application to noise suppression within ducts in aero-engines, gas turbines, blowers and various mufflers [5,6,7,8,9,10]. Additionally, [12,14] consider mode-matching for finite lined region, [13] examines the relationship between the the nature of the source and the transmitted power whilst [11] discusses the form of the additional wavefunctions required at an exceptional point.…”

Section: Introductionmentioning

confidence: 99%

Mode coalescence and the Green’s function in a two-dimensional waveguide with arbitrary admittance boundary conditions

Perrey‐Debain

Nennig

Lawrie

2022

Journal of Sound and Vibration

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“…Further notable extensions from the same decade include the works by Zorumski and Mason [6] who extended Tester's analysis to circular ducts with locally reacting liners and Koch [7] who used a Wiener-Hopf approach to study acoustic power attenuation in a duct with multiple sections of lining. Cremer's concept received little further attention until quite recently when a number of papers exploring the idea in the context of noise attenuation within circular and/or annular ducts with flow [8][9][10][11][12][13] appeared in the literature. It is worth noting that EPs also occur in phenomena such as zeros in group velocity [14] or instability in, for example, thermoacoustics [15].…”

Section: Introductionmentioning

confidence: 99%

Analytic mode-matching for accurate handling of exceptional points in a lined acoustic waveguide

2022

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Exceptional points (which occur when two or more modes coalesce) have long been associated with optimal attenuation in lined acoustic waveguides. In recent years, with a view to optimizing sound absorption, some effort has gone into designing liners that generate exceptional points (EPs) at specified frequencies. However, analytic modelling of acoustic scattering in the presence of an EP is not well developed, with most authors relying on standard methods applied close to (but not at) EP conditions. Indeed, exact treatment requires care since the mathematical system under-pinning the scattering process is degenerate. This article presents an analytic mode-matching approach to modelling the scattering of a plane wave travelling towards the junction of a rigid duct with a lined duct at EP conditions. Both EP2 and EP3 (coalescence of two and three modes respectively) are considered. The enhanced mode-matching scheme is shown to be valid and numerically robust, and it is anticipated that it will be straightforward to adapt to a wide range of applications involving complex symmetric operators.

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Optimum acoustic impedance in circular ducts with inviscid sheared flow: Application to turbofan engine intake

Cited by 12 publications

References 32 publications

Design of a single degree of freedom acoustic liner for a fan noise test rig

Design of a single degree of freedom acoustic liner for a fan noise test rig

Mode coalescence and the Green’s function in a two-dimensional waveguide with arbitrary admittance boundary conditions

Analytic mode-matching for accurate handling of exceptional points in a lined acoustic waveguide

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