Numerical prediction of airborne noise transmission into a fuselage

Accurate prediction of airborne noise transmiasion through the fuselage requires a detailed knowledge of the magnitude and phase variation of the incident and scattered acoustic pressure fields, and a method of predicting the coupled structural-acoustic response of the fuselage (and its interior) excited by the above prwure fields. This paper presents a numerical method for predicting the above effects. The scattering effects are predicted by a combination of several numerical methods such as finite elementa,integral equations and fast Fourier transforms. The coupled structural-acoustic response of the fuselage is predicted by the Gnite element method. For initial demonstration purposes, the predicted results are compared in this paper with analytic aolutions for the problem of scattering of noise from a line source by an in6nitely long thin cylinder, and transmission into its interior. Excellent agreement between numerical and analytical results suggests that by using these computational tools, it should be possible to predict the structural response and transmitted noise at frequencies comparable to the first blade passage frequency in an advanced propeller driven aircraft, M long M the incident pressure field trom the propeller can be accurately quantified, and M long M an adequate number of nodes are used to model the coupled structural-acoustic system. The eventual goal of this project is to develop computational tools for predicting scattering and transmission of noise from a propeller into a fuaelage, including the various difFraction and boundary layer refraction effects that are present in a commercial aircraft flying at a traamnic speed.