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Content archived on 2024-04-19

Aeroacoustics Methods for Fan-Noise Prediction and Control


The objective of this programme is to provide European air-frame and nacelle manufacturers with the technology required to control fan tone noise on future civil transport aircraft equipped with advanced high-bypass-ratio (HBR, typically 6:1), very-high-bypass-ratio (VHBR, typically 9:1) or ultra-high-bypass-ratio (UHBR, typically 12:1-15:1), turbofans. Fan noise is predicted to be one of the most important noise sources on HBR, VHBR and UHBR engines and must be controlled if aircraft are to meet future community noise regulations.
The FANPAC programme has addressed the opportunities for noise reduction at source by first developing an improved understanding of the noise source generation mechanisms. A considered and focused approach to noise reduction follows from this understanding. Similarly the optimisation of noise reduction by conventional and novel acoustic liners follows from both a microscopic understanding of the internal liner behaviour and a macroscopic understanding of the propagation of sound over complex impedance structures.

The development of understanding of the noise generation mechanisms in this programme has resulted principally from the testing of the model fan at a range of conditions in several different configurations and equipped with advanced acoustic and aerodynamic instrumentation.

To assess the potential benefit from novel, non-locally reacting, acoustic liners, a two step approach was taken by first analytically modelling the liner behaviour in response to an applied sound field to determine impedances or characteristic properties and validating the model with laboratory impedance tests and second by developing attenuation prediction models for lined ducts.
Considerable process has been made over the last 3 1/2 years towards the targets originally set. Studies into the human sensitivity to buzz saw noise have helped identify the problems for controlling cabin noise. There is potential to reduce fan noise by up to 5dB at some conditions through source noise control and the use of acoustic liners. Other technologies such as active noise control may offer further benefits.
Research in this field is required to keep European aircraft, aero-engine and nacelle manufacturers competitive with regard to the US.

The objectives of the work are:

i) To establish the physical mechanisms responsible for the generation of fan tones, and to validate aero-acoustic models for predicting fan tone levels,
ii) To explore novel methods for controlling fan tone generation at source (in particular buzz-saw tones),
iii) To develop codes to predict noise attenuations by non-locally-reacting liners and non-axisymmetric liners,
iv) To develop a semi-empirical/theoretical model of wake propagation,
v) To design and test novel 500-5000 Hz acoustic liners for fan noise control, and to validate models for predicting liner performance,
vi) To perform tests using a model fan rig to validate community and cabin noise prediction methods,
vii) To improve community and cabin fan tone noise prediction methods and to assess various techniques to control fan noise, aiming to reduce community noise levels by typically 4dB and cabin buzz-saw noise levels by typically 5-10dB.


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United Kingdom

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Participants (11)