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The University of Southampton

Research project: Mode-matching for duct acoustics

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We have developed a method to predict how sound is attenuated in ducts and waveguides with complex distribution of acoustic treatments.

Diagram of a lined duct with a hard patch.
A lined duct

On aircraft turbofan engines, hard patches are small areas of a liner where the acoustic treatment has been removed either for design or maintenance purposes. These patches are detrimental to the performance of liners as they reduce the area of treated surfaces. They also introduce significant modal scattering by redistributing the acoustic energy onto low-order modes which are less attenuated. Being able to predict efficiently there impact on the performance of acoustic treatment is particularly important.

Example of predicted sound directivity
Predicted sound directivity

For this purpose we have developed new mode-matching techniques to build a description of the sound field in the duct. Compared to fully numerical methods, mode-matching techniques are much faster but limited to canonical geometries. A finite element method has been develop to obtain the acoustic modes of a duct. The use of finite element methods instead of purely analytical techniques allows for ducts with arbitrary cross sections, liner distributions and flow profiles. An eigenvalue problem based on Pridmore-Brown's equation is solved using standard finite elements.

Associated research themes


Fluid Dynamics

Related research groups

Acoustics Group


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