Sound Transmission through Aircraft Fuselage Structures

Abstract

Theoretical and empirical studies of sound transmission through an aircraft fuselage have been performed and prediction methods developed for determining the interior noise levels due to boundary-layer turbulence and jet-noise excitation. The aircraft fuselage is evaluated by considering three equivalent structural models to represent the entire frequency range of interest. The fuselage reponse at low frequencies is determined from the characteristics of a stiffened cylindrical shell, while the fuselage responses at intermediate and high frequencies are determined from the characteristics of a stiffened panel group and a single panel, respectively. In each case, the equivalent structure and interior acoustic field are treated as a coupled dynamic system whose response is describable in terms of the system normal modes and coupled natural frequencies. Computer programs have been developed for the determination of the applied fluctuating pressures, sound transmission losses, and interior acoustic fields associated with fuselage structures; the geometry of the fuselage, properties of the acoustic treatment and aircraft flight condition are variable input parameters. The program may be used to determine the significant parameters affecting sound transmission and to optimize acoustic treatments within the scope of specific structural design variations.