Abstract
An existing theoretical model to predict the pressure levels on an aircraft's fuselage is improved by incorporating a more physically realistic method to predict fan tone radiation from the intake of an installed turbofan aero-engine. Such a model can be used as part of a method to assess cabin noise. Fan tone radiation from a turbofan intake is modelled using the exact solution for the radiated pressure from a spinning mode exiting a semi-infinite cylindrical duct immersed in a uniform flow. This approach for a spinning duct mode incorporates scattering/diffraction by the intake lip, enabling predictions of the radiated pressure valid in both the forward and aft directions. The aircraft's fuselage is represented by an infinitely long, rigid cylinder. There is uniform flow aligned with the cylinder, except close to the cylinder's surface where there is a constant-thickness boundary layer. In addition to single mode calculations it is shown how the model may be used to rapidly calculate a multi-mode incoherent radiation from the engine intake. Illustrative results are presented which demonstrate the relative importance of boundary-layer shielding both upstream and downstream of the source, as well as examples of the fuselage pressure levels due to a multi-mode tonal source at high Helmholtz number.
Highlights
In modern civil aircraft, turbofan jet engines are the dominant noise source during take-off and cruise
Installation acoustics for turbofan jet engines refers to the study of how the radiated noise is affected when an engine is installed on an airframe
Fan tones radiating from an engine intake duct
Summary
Turbofan jet engines are the dominant noise source during take-off and cruise. In McAlpine, Gaffney and Kingan [10] the pressure levels on a cylindrical fuselage forward of the intake duct were simulated using a theoretical solution based on an incident field given by a distributed “disk”
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