Asymptotic approximations for sound generated by aeroengines Seminar

One of the principal mechanisms for sound to be generated in an aeroengine is by the interaction of an O(1) background flow with cascades of thin blades. Wakes the form behind the rotors can be modelled as an unsteady vortical perturbation to the (assumed steady) background flow. This unsteady "gust" interacts with a second layer of blades, stators, generating noise. This so called gust-aerofoil interaction is typically studied in uniform steady flows, however significant structural components within the engine could well impose a sheared background flow. Furthermore sound can propagate upstream towards the rotors where understanding sound-aerofoil interaction becomes crucial to determining the noise exiting the engine via the intake duct.

This talk will therefore discuss analytic approximations, found using the method of matched asymptotic expansions, for the sound generated by high-frequency gust-aerofoil interactions in steady uniform and shear flows as well as high-frequency sound-aerofoil interaction in steady uniform flow. Comparisons between these asymptotic approximations and numerical or experimental results will be given where possible.