Calculation of acoustic transfer functions for smooth ducts of varying cross section and non-uniform mean flow using eigen analysis in general curvilinear coordinates

Wilson, Alexander G. (2018) Calculation of acoustic transfer functions for smooth ducts of varying cross section and non-uniform mean flow using eigen analysis in general curvilinear coordinates. In 2018 AIAA/CEAS Aeroacoustics Conference. American Institute of Aeronautics and Astronautics.. (doi:10.2514/6.2018-3776).

Abstract

The EAGCC (Eigen Analysis in General Curvilinear Coordinates) method, based on the linearised Euler equations for isentropic perturbations, is extended to include an improved non-iterative solution methodology, an acoustic liner boundary condition and a Ffowcs-Williams/Hawkings surface for calculation of farfield acoustic pressures. Three validation cases are presented, testing the accuracy of the extended method to predict acoustic transmission across a geometric duct transition, an acoustically lined duct section, transition to external near-field flow at duct inlet and farfield acoustic pressure calculations. It is shown that there is a practical limit to the wavelengths that can be modelled. Taking a typical aeroengine inlet as an example, circumferential harmonics can be calculated up to between 40 or 60 depending on the complexity of the case. Under this limit the elapsed time for a complete calculation will range from a few minutes to a few hours on a current compute platform. All three testcases show good agreement between the EAGCC method and reference calculations. These test cases confirm that the EAGCC method has wide potential for industrial application to acoustic propagation, both in duct and to the farfield.

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