The prediction of upstream noise generated by aeroengine components including acoustic liners under realistic flight conditions is an important tool for the aircraft design process. In general, the acoustic absorbing properties of liners and the resulting noise mitigation are affected by the presence of the boundary layer. The main goal of this study is to compare the effect of liner attenuation in the far field for different boundary conditions representing the liners, including uniform and shear flows, and consider typical turbofan geometry and operating conditions. For uniform flow cases, a reference solution was obtained from a finite element method code and used to validate the analytical model, which is based on the in-duct mode-matching technique and an analytic radiation model. For shear flow cases, the Brambley boundary condition and the solution to the Pridmore–Brown equation were considered; and the power transmission and modal decay rate along the duct were compared for increasing boundary-layer thickness. The transmitted modes were coupled to the radiation model based on the Kirchhoff integral approximation. The results suggest that the influence of the boundary-layer thickness can lead to a significant reduction on liner attenuation in some conditions. Moreover, it was observed in some cases that modal scattering produced by liner discontinuities results in a complex behavior (with the redistribution of the acoustic energy onto cut-on modes) in terms of noise radiation.
Intake Fan Noise Attenuation due to Liners Considering Uniform and Shear Flows
AIAA Journal ; 57 , 8 ; 3480-3492
2019-06-11
13 pages
Article (Journal)
Electronic Resource
English
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