The radiation of high frequency sound out of a jet pipe

Abstract

A simple model problem is first discussed: the radiation of sound out of a semi-infinite cylindrical pipe, with internal and external flows. Two approximate high frequency solutions are presented, one based on Kirchhoff's approximation and the other in the spirit of the geometrical theory of diffraction, and are compared with Munt's [2] exact solution by the Wiener-Hopf technique. The radiation from a jet emerging from an orifice in a baffle plate is also discussed. Next, the differences between this simple model and an aero engine configuration are considered, shoqing how the results are modified by the presence of a secondary flow (e.g., the fan stream on a turbofan engine), by the contraction of the final nozzle, and by the presence of many duct modes in the pipe.