Theoretical methods for the prediction of near-field and far-field sound radiation of fan tones scattered by a cylindrical fuselage

Abstract

The aim of the work presented in this paper is the development of theoretical methods to predict scattering of fan tone noise from a turbofan engine by the airframe fuselage. The analysis begins with an overview of previous research on fan tone noise scattering by an adjacent cylindrical fuselage. In all similar previous work the propagation of sound through the fuselage boundary layer has been calculated using numerical methods. The effect of the boundary layer can be very significant on the upstream radiated sound from a turbofan’s intake. An asymptotic approach is presented to model sound propagation within the boundary layer.
An entirely analytic formulation is derived for a thin linear velocity profile. This approach leads to a far-field solution expressed in terms of a Fourier series, and a near-field solution expressed in terms of a Fourier series and a Fourier inverse transform. The new formulation is validated by comparison with simpler analytic solutions, and against existing numerical solutions. Furthermore, the results using a linear velocity profile are shown to be comparable with numerical results calculated with a realistic shear velocity profile that closely matches a turbulent boundary layer. Preliminary results from the new theoretical method are presented that illustrate the refraction effect by the fuselage boundary layer.

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Identifiers

ORCID for Dionysios-Marios Rouvas: orcid.org/0009-0001-6646-4444

ORCID for Alan McAlpine: orcid.org/0000-0003-4189-2167

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