Analysis of the Transmission of Sound into the Passenger Compartment of a Propeller Aircraft Using the Finite Element Method

摘要

The double wall construction of an aircraft cabin was analyzed to see if sound transmission phenomena found in experiments can be reproduced. The eigenvalues and eigenmodes of the plane cross section were calculated, with and without the inner trim pannels, emphasizing the effects of different attachment of the trim panels to the frames and also of the weight and stiffness of the trim panels. The calculated modes were used to calculate the sound levels arising from an external pressure field acting on the outer shell. The analysis is performed with the finite element system ASKA-acoustics. The intervention between the structural parts and the fluid in the different cavities is modeled with a symmetric coupling formulation with pressure and displacement potential as fluid degrees of freedom. The acoustic field is modeled with special acoustic finite elements and the coupling to the structure is handled with interface elements. Analysis of an aircraft cross section shows that the transmission of low frequency sound is strongly dependent on the dynamics of the fuselage-air-trim-air system. The maximum SPL may vary from 123 down to 118 dB in the extreme cases where only attachment and density of the trim panel are changed. The results also show that a porous absorbent in the air space may give an additional decrease down to a maximum of 114 dB by carefully tuning the mass density of the porous material.