A Hybrid Spectral Analysis of Noise Radiated from Non-Axisymmetric Turbofan Inlets

A new 3D analysis of tone noise radiated from non-axisymmetric turbofan inlets is introduced in this paper. The new analysis combines a standard nite element approximation of the acoustic eld in the axial and radial coordinates with a Fourier spectral representation in the circumferential direction. The boundary conditions at the fareld, fan duct and acoustic liners are treated using the same spectral representation. The new method is signicantly less expensive than a conventional 3D nite element approach because relatively few circumferential Fourier modes need to be retained in the solution for an accurate eld representation. The discrete acoustic equations are solved iteratively using the popular BICGSTAB or QMR algorithms, also exploiting an axisymmetric approximation of the inlet geometry to form an effective preconditioner. The method is demonstrated on testcases of practical relevance, with emphasis on the modelling of circumferentially non-uniform acoustic liners.