Design of Acoustic Linings for Ducts with Flow

Eversman, Walter; Nelsen, M. D.; Armstrong, D. L.; Hall, Orville J.

doi:10.2514/3.59034

Cited by 11 publications

(2 citation statements)

References 14 publications

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“…In general, viscous and radiation effects at the holes are computed analytically, whereas non-linear effects are best-fitted to experimental data. Several models have been proposed over the past years, with special attention to nonlinear regimes 21,22 i.e. grazing flow and high sound pressure level.…”

Section: Impedance Modelsmentioning

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: Impedance Modelsmentioning

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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“…According to this Cremer criterion, it appears that the maximum attenuation occurs when the wavenumbers of the two lowest transverse modes coalesce. Cremer optimum criterion has been one of the most important tool for duct liner design [2,4,5,6,7,8,9,10], and it has been revisited recently in references [11] [12]. It is true that if a source is dominated by a single transverse mode, considering the attenuation of each mode individually may describe the Total Sound Power (TSP) attenuation.…”

Section: Introductionmentioning

confidence: 99%

Spatial transient behavior in waveguides with lossy impedance boundary conditions

Guo,

Liu,

et al. 2020

Preprint

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Attenuation in acoustic waveguides with lossy impedance boundary conditions are associated with non-Hermitian and non-normal operators. This subject has been extensively studied in fundamental and engineering research, and it has been traditionally assumed that the attenuation behavior of total sound power can be totally captured by considering the decay of each transverse mode individually. One of the classical tools in this context is the Cremer optimum concept that aims to maximize the attenuation of the least attenuated mode. However, a typical sound field may be a superposition of a large number of transverse modes which are nonorthogonal, and the individual mode attenuation may have little to do with the total sound power attenuation. By using singular value decomposition, we link the least attenuated total sound power to the maximum singular value of the non-normal propagator. The behaviors of the least attenuated total sound power depend only on the lossy boundary conditions and frequency, but are independent of sources. The sound may be almost non-decaying along the waveguide transition region for any lossy impedance boundary conditions although all modes attenuate exponentially. This spatial transient appears particularly strongly if the impedance is close to an exceptional point of the propagator, at which a pair of adjacent modes achieve maximum attenuation predicted by Cremer optimum concept. These results are confirmed using non-modal numerical calculations and a two-by-two toy model.

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

Spillere

Cordioli

2019

Journal of Sound and Vibration

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Design of Acoustic Linings for Ducts with Flow

Cited by 11 publications

References 14 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

Spatial transient behavior in waveguides with lossy impedance boundary conditions

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

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