dc.description.abstract | This thesis considers the sound generated by unsteady perturbations interacting with
solid aerofoils in background steady flows, in an attempt to further develop analytic models for the noise generated by blades within turboengines. Specifically, high-frequency
unsteady gust and sound wave perturbations are considered and asymptotic results are
obtained for, primarily, the far-field noise.
Previous analytic work has examined high-frequency gust-aerofoil interactions in steady
uniform flows using rapid distortion theory, and has focused on aerofoils with simple
geometries. We extend this to deal with aerofoils with more realistic geometries (by
including camber, thickness, and angle of attack), as well as considering the new topic of
sound-aerofoil interactions in steady uniform flows for aerofoils with realistic geometries.
The assumption of a steady uniform flow is later relaxed and we investigate the sound
generated by high-frequency gust-aerofoil interactions in steady shear flows.
Throughout all of the aforementioned work, the key process involves identifying various
asymptotic regions around the aerofoil where different sources dominate the generation of
sound. Solutions are obtained in each region and matched using the asymptotic matching
rule. The dominant regions producing noise are the local, “inner”, regions at the leading
and trailing edges of the aerofoil. Approximations for the far-field noise (in the “outer”
regions) are the principal results, however one can also extract approximations for the
unsteady pressure generated on the surface of the aerofoil.
The surface pressure generated by high-frequency gust-aerofoil interaction in uniform
flow is found to contain a singularity at the leading-edge stagnation point, thus the final
piece of work in this thesis focuses more closely on turbulent interactions with solid body
stagnation points in uniform flow, eliminating this singularity. | |