Back-to-back comparison of impedance measurement techniques applied to the characterization of aero-engine nacelle acoustic liners

Ferrante, Pier Giorgio; Roeck, Wim De; Desmet, Wim; Magnino, N.

doi:10.1016/j.apacoust.2015.12.004

Cited by 17 publications

(16 citation statements)

References 15 publications

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“…Impedance eduction methods have received growing attention over the past decades (e.g. [26,27]). These methods avoid instrumentation of the liner sample, which could potentially affect its own impedance, and instead focus on the instrumentation of test rigs, with flush-mounted microphones at the duct walls the most popular choice (e.g.…”

Section: B Impedance Eduction Methodsmentioning

confidence: 99%

“…These methods avoid instrumentation of the liner sample, which could potentially affect its own impedance, and instead focus on the instrumentation of test rigs, with flush-mounted microphones at the duct walls the most popular choice (e.g. [12,26]). From that, governing equations of the acoustic propagation are necessary in order to relate measurements with a numerical model of the acoustic field.…”

Section: B Impedance Eduction Methodsmentioning

confidence: 99%

“…where i = √ −1, = / 0 is the free-field wavenumber and ℎ is the cavity height. In practice, this impedance must be corrected to account for the presence of small pressure transducers which are inserted into the honeycomb cavity [26]. However, numerical simulations do not suffer from this limitation, and therefore no corrections need to be made.…”

Section: A In-situ Techniquementioning

confidence: 99%

See 2 more Smart Citations

Numerical Investigation of Acoustic Liners Experimental Techniques using a Lattice-Boltzmann Solver

Schroeder

Spillere

Bonomo

et al. 2021

Aiaa Aviation 2021 Forum

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The physics behind acoustic liners attenuation in the presence of flow and high sound pressure level is still a matter of debate. Similarly, discrepancies between experimental results and numerical data have been linked to the boundary conditions used to model the liner and boundary layer effects, and the reasons behind these discrepancies are still not clear. In this sense, to avoid the limitations of the boundary condition approach, fully resolved high fidelity computation models of the liner and its dissipation mechanisms may be an important tool to improve understanding. The present study carries out a numerical analysis using a code based on the Lattice-Boltzmann method, and special focus is given on replicating the results from different experimental techniques used to evaluate the liner impedance: the in-situ method and an impedance eduction method based on the mode-matching technique. The study is conducted with a model including a single degree of freedom liner with multiple cavities based on a real geometry. The model considers high sound pressure level, grazing plane acoustic waves without flow in order to replicate the experimental setup. A mesh convergence analysis is performed, and the liner impedance obtained numerically is compared with experimental results from the in-situ method and the impedance eduction technique. The numerical pressure and velocity fields are also analyzed in detail to better understand the damping mechanisms and physics involved.

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Section: B Impedance Eduction Methodsmentioning

confidence: 99%

Section: B Impedance Eduction Methodsmentioning

confidence: 99%

Section: A In-situ Techniquementioning

confidence: 99%

See 1 more Smart Citation

Numerical Investigation of Acoustic Liners Experimental Techniques using a Lattice-Boltzmann Solver

Schroeder

Spillere

Bonomo

et al. 2021

Aiaa Aviation 2021 Forum

View full text Add to dashboard Cite

show abstract

“…Although very convenient from the practical point of view, this termination introduces uncertainties in the low frequency range due to the apparent mismatch between impedance tube area and exposed honeycomb area. 31 A broadband source has been used to measure the liner impedance between 500 Hz and 6400 Hz at overall sound pressure levels (OASPLs) up to 150 dB. The non-linearity factor (NLF) and effective percentage of open area were obtained with pure tones at increasing levels close to the liner resonance frequency.…”

Section: Normal Incidence Impedance Measurementsmentioning

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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“…3 The direct eduction methods allows the impedance evaluation by means of the wavenumber of the lined section extracted using Prony-like algorithms. 7 Ferrante et al 8 compared the in situ with an impedance eduction technique based on the two-port matrix (for both no-flow and grazing flow conditions) and with a normal incidence impedance tube (only no-flow). The results suggested good agreement between the in situ technique with both reference methods, although some discrepancies were observed, especially with grazing flow.…”

Section: Introductionmentioning

confidence: 99%

A comparison of in situ and impedance eduction experimental techniques for acoustic liners with grazing flow and high sound pressure level

Bonomo,

Quintino,

Spillere

et al. 2024

International Journal of Aeroacoustics

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Several techniques are available to characterize acoustic liners when subject to grazing flow and high sound pressure level (SPL). Although the in situ technique started as the primary experimental procedure, impedance eduction techniques have gained popularity over the past years. However, there is a lack of comparison between these group of methods, especially at conditions typically found in turbofan engines. In this work, in situ and impedance eduction techniques are compared at high flow velocities and SPL using typical acoustic liner test samples and considering uniform flow. Both upstream and downstream acoustic wave propagation will also be considered in view of the discrepancies recently observed by eduction methods. A new method to compensate the instrumentation effect in the in situ technique is proposed and validated. Results are obtained for bulk Mach numbers up to 0.5 and SPLs up to 145 dB for both in situ and two eduction techniques. The three methods presents good agreement in the absence of flow. Unexpected results are observed with higher flow Mach numbers using the eduction technique.

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Back-to-back comparison of impedance measurement techniques applied to the characterization of aero-engine nacelle acoustic liners

Cited by 17 publications

References 15 publications

Numerical Investigation of Acoustic Liners Experimental Techniques using a Lattice-Boltzmann Solver

Numerical Investigation of Acoustic Liners Experimental Techniques using a Lattice-Boltzmann Solver

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

A comparison of in situ and impedance eduction experimental techniques for acoustic liners with grazing flow and high sound pressure level

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