Reduction of Aeroengine Tonal Noise using Scattering from a Multi-Segmented Liner

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• Tom Law (Acoustics lab, University of Cambridge)
• Friday 23 May 2008, 12:00-13:00
• Language Unit Meeting Room.

If you have a question about this talk, please contact Simon Illingworth.

A recent trend in aeroengine inlet liner design has been to improve liner performance by eliminating the joints between liner segments. The resulting reduction in modal scattering has produced substantial acoustic benefits for the relatively short liners in the inlet. In contrast, the available surface area for lining downstream of the fan is significantly greater. This provides an opportunity to use several liner segments with different properties so that the source noise can be more effectively mitigated. This paper investigates the opportunity for increasing the attenuation of downstream propagating tonal noise using inter-liner scattering. This is achieved by changing the axial sequencing of seven different cylindrical segments that were originally optimised to attenuate the broadband source noise. The fully scattered field for all possible segment permutations is computed in order to establish the optimum segment order and elucidate the principles behind the exploitation of inter-liner scattering. A simple reordering of the absorbers is shown to provide a significant range in overall attenuation and this range increases with the length of the absorbers. The results are analysed by considering the changes in the modal distribution of downstream propagating energy along the duct in order to explain why some liner sequences are more effective than others. The best sequences present the most effective absorbers with a radial mode energy distribution that can be more readily attenuated. This means that all the scattering events that occur upstream of a liner can be significant and the performance of a liner will be based on the configuration of the system, not just localised effects. In general, axial scattering has a detrimental effect on overall liner performance when a large number of modes are cut-on. The importance of the source characteristics are highlighted by changing the number of fan stators to reduce the number of radial modes cut-on. This allows inter-liner scattering to be more effectively exploited. In summary, the analyses suggest that the ordering of absorbers should be a key part of any multi-segmented liner optimisation.

This talk is part of the Engineering Department Acoustics/Combustion Student seminars series.

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• Engineering Department Acoustics/Combustion Student seminars
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