Rolls-royce Corporation

Peter J G Schwaller

Nigel H S Smith

Noise control with respect to rotating machinery such as gas turbine engines is important to meet acceptable operational and environmental constraints. Buzz-saw noise in particular is due to differences in blade to blade geometries both as assembled and due to blade manufacturing tolerance variations. Generally, a plurality of blades rotate within a duct and some noise propagates forwards of the blade assembly. In order to abate such noise an acoustic lining is provided. By consideration of the acoustic attenuation effects of that lining, it is possible to rearrange the blades within the blade assembly such that the overall noise attenuation effects are improved. Thus, the blade assembly may be rearranged such that there is a reduction in the Fourier coefficients at harmonics above and below the harmonics most attenuated by the acoustic attenuation treatment or lining or alternatively the effect of that lining maximized by rearrangement of the blades to shift the harmonics to those most attenuated by the acoustic treatment.

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Derby, United Kingdom

Peter J G Schwaller