Folded Cavity Liners for Turbofan Engine Intakes

Sugimoto, Rie; Murray, Paul; Astley, R.J.

doi:10.2514/6.2012-2291

Cited by 12 publications

(14 citation statements)

References 3 publications

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“…Additionally, boundary layers refract the upstream propagating sound away from the duct wall, which can affect the effective liner attenuation, see Refs. [11,21,27]. Some or all of these differences between the model and reality may account for the differences observed between measurement and prediction for supersonic fan "buzz-saw" tones produced in an aircraft engine's intake duct.…”

Section: Discussionmentioning

confidence: 99%

“…Modern intake ducts have acoustic linings installed on the duct wall. The acoustic liners can be tuned to target a prescribed frequency range [21]. In fact it is not uncommon to have a liner installed close to the fan followed by a different liner which covers the rest of the lined area inside the intake barrel.…”

Section: Frequency-domain Methodsmentioning

confidence: 99%

“…In fact it is not uncommon to have a liner installed close to the fan followed by a different liner which covers the rest of the lined area inside the intake barrel. High-amplitude low-frequency tones could be targeted close to the fan, whereas further upstream of the fan, the aim is to attenuate the higher-frequency sound [21]. Therefore, propagation models for realistic intake ducts must take into account the nonlinear attenuation of the shock waves and the effect of sound absorption by the installed acoustic liners.…”

Section: Frequency-domain Methodsmentioning

confidence: 99%

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Nonlinear Propagation of Supersonic Fan Tones in Turbofan Intake Ducts

2018

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Supersonic fan tones are a critical issue for large fans; it is well known that these tones are a key noise source at high power operating conditions for modern turbofan aero-engines. Nonlinear propagation of the rotor-locked pressure field generated in a turbofan intake duct is calculated by implementing nonlinear weak-shock theory numerically via a combined time-frequency domain algorithm. The aim of the prediction method is to model the nonlinear attenuation and liner absorption of the rotor-locked pressure field within the intake duct. In this hybrid method, the time-domain approach provides a robust and accurate prediction of the non-linear attenuation while the fre-

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Section: Discussionmentioning

confidence: 99%

Section: Frequency-domain Methodsmentioning

confidence: 99%

Section: Frequency-domain Methodsmentioning

confidence: 99%

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Nonlinear Propagation of Supersonic Fan Tones in Turbofan Intake Ducts

2018

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“…For time-harmonic excitation, the total pressure field in the impedance tube can be expressed byP ðyÞ ¼Ãe jky þBe Àjky (11) whereÃ andB are arbitrary complex constants which represent the amplitude and the relative phase of plane waves travelling in the positive and negative y direction, respectively. From the linearised equation of momentum conservation (equation (2)), the acoustic particle velocity is given byũ ðyÞ ¼Ã e jky ÀBe Àjky q 0 c 0 (12) Therefore, the normalized specific acoustic impedance, from equations (11) The above expression for the impedance at the facing sheet is modified as the amplitudes of the incoming and outgoing waves cannot be measured at H c . The total pressure at the inlet plane can be calculated from COMSOL.…”

Section: Impedance Calculationmentioning

confidence: 99%

Slanted septum and multiple folded cavity liners for broadband sound absorption

Palani

Murray

McAlpine

et al. 2021

International Journal of Aeroacoustics

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The design of acoustic liners with complex cavities for a wide frequency range of attenuation using numerical method is investigated in this paper. Three novel liner concepts are presented, demonstrating predicted improvements in broadband sound absorption when compared with that for conventional designs. The liners include a slanted septum core, a slanted septum core with varying percentage open area, and a MultiFOCAL concept. A finite element model of a normal incidence impedance tube is developed using COMSOL Multiphysics modeling software to predict the acoustic properties (resistance and reactance) of liners at medium and high sound pressure levels, and to study the impact of variations in the liner design parameters. The impedance tube finite element model incorporates non-linear semi-empirical impedance equations, validated by comparing numerical results with measurements performed on a single-degree-of-freedom liner, with a perforated face sheet, at high sound pressure level. The design variables of the novel liner concepts are optimized using a hybrid automated optimisation procedure. The low-frequency optimum slanted septum core concept with an open area of 4.5% for the face sheet and 18% for the short slanted septum is predicted to have an absorption level of at least 14 dB in the frequency range of 400–1000 Hz for normally incident pure tone excitations at 150 dB. The slanted septum core concept with varying percentage open area, with broadband optimum design variables, is predicted to have good broadband sound absorption levels of at least 10 dB in the frequency range of 570–3800 Hz. Finally, the MultiFOCAL liner concept with optimised percentage open areas is predicted to have an excellent broadband sound absorption levels of at least 14 dB, for pure tone excitations at 150 dB, in the frequency range of 900–5300 Hz. This work will be followed by optimisation of the face sheet geometries of these novel liner designs in order to maximise lined duct attenuation for aircraft engine applications.

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“…Unfortunately, the relatively low frequency of these disturbances means a simple acoustic liner design would have to be sufficiently deep to attenuate the pressure waves and ultimately have any impact on fan stability [15,27], Such a liner would be impossible to use in a typical civil aero-engine intake. It may be possible to use more advanced designs, such as folded-cavity liners [30].…”

Section: Fig 5: Aero-damping As a Function Of Frequency (Left) And Inmentioning

confidence: 99%

A Review of Computational Aeroelasticity Of Civil Fan Blades

Vahdati

Lee²,

Sureshkumar

2020

JGPP

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This paper presents a review of aeroelasticity research concerning fan blades in modern civil aircraft engines. It summarises the research carried out at the Rolls-Royce Vibration University Technology Centre (VUTC) at Imperial College over the past 25 years. The purpose of this paper is to gather information on all the aeroelastic issues observed for civil aero-engine fan blades into one document and provide a useful synopsis for other researchers in the field. The results presented here are based on numerical methods but wherever possible data from experiments are used to verify the numerical findings. For cases where such datasets do not exist fundamental principles, engine observations and engineering judgement are used to support the numerical results. Numerical methods offer a cheaper alternative to rig tests, especially in cases of blade failure, and can also provide more information about the nature of instabilities, which can be useful in the design of future civil aircraft engines. In fact, in cases such as crosswind testing that use smaller rig-scale blades, such results can even be more representative of real engine flows.

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Folded Cavity Liners for Turbofan Engine Intakes

Cited by 12 publications

References 3 publications

Nonlinear Propagation of Supersonic Fan Tones in Turbofan Intake Ducts

Nonlinear Propagation of Supersonic Fan Tones in Turbofan Intake Ducts

Slanted septum and multiple folded cavity liners for broadband sound absorption

A Review of Computational Aeroelasticity Of Civil Fan Blades

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