โ Scribed by M.E. GOLDSTEIN; S.J. LEIB
No coin nor oath required. For personal study only.
An approximate method for calculating the noise generated by a turbulent #ow within a semi-in"nite duct of arbitrary cross-section is developed. It is based on a previously derived high-frequency solution to Lilley's equation, which describes the sound propagation in a transversely sheared mean #ow. The source term is simpli"ed by assuming the turbulence to be axisymmetric about the mean #ow direction. Numerical results are presented for the special case of a ring source in a circular duct with an axisymmetric mean #ow. They show that the internally generated noise is suppressed at su$ciently large upstream angles in a hard-walled duct, and that acoustic liners can signi"cantly reduce the sound radiated in both the upstream and downstream regions, depending upon the source location and Mach number of the #ow.
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