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SUMMARY:Reduction of Aeroengine Tonal Noise using Scattering from a Multi-
 Segmented Liner - Tom Law (Acoustics lab\, University of Cambridge)
DTSTART:20080523T110000Z
DTEND:20080523T120000Z
UID:TALK12302@talks.cam.ac.uk
CONTACT:Simon Illingworth
DESCRIPTION:A recent trend in aeroengine inlet liner design has been to im
 prove liner performance by eliminating the joints between liner segments. 
 The resulting reduction in modal scattering has produced substantial acous
 tic benefits for the relatively short liners in the inlet. In contrast\, t
 he available surface area for lining downstream of the fan is significantl
 y greater. This provides an opportunity to use several liner segments with
  different properties so that the source noise can be more effectively mit
 igated. This paper investigates the opportunity for increasing the attenua
 tion of downstream propagating tonal noise using inter-liner scattering. T
 his is achieved by changing the axial sequencing of seven different cylind
 rical segments that were originally optimised to attenuate the broadband s
 ource noise. The fully scattered field for all possible segment permutatio
 ns is computed in order to establish the optimum segment order and elucida
 te the principles behind the exploitation of inter-liner scattering. A sim
 ple reordering of the absorbers is shown to provide a significant range in
  overall attenuation and this range increases with the length of the absor
 bers. The results are analysed by considering the changes in the modal dis
 tribution of downstream propagating energy along the duct in order to expl
 ain why some liner sequences are more effective than others. The best sequ
 ences present the most effective absorbers with a radial mode energy distr
 ibution that can be more readily attenuated. This means that all the scatt
 ering events that occur upstream of a liner can be significant and the per
 formance of a liner will be based on the configuration of the system\, not
  just localised effects. In general\, axial scattering has a detrimental e
 ffect 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. Th
 is allows inter-liner scattering to be more effectively exploited. In summ
 ary\, the analyses suggest that the ordering of absorbers should be a key 
 part of any multi-segmented liner optimisation.
LOCATION:Language Unit Meeting Room
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