Cacciolati C., Guyader J., Neple P.

The turbulent boundary layer excitation of an aircraft cockpit is one of the major interior noise sources over a large frequency range. In the context of understanding and predicting this airborne sound transmission typically a diffuse sound field excitation is used. Although many authors studied the vibroacoustic behaviour of aeronautical structures under a diffuse sound field excitation or a turbulent boundary layer one, none of them made a comprehensive comparison over a large frequency range. The main objective of this work is to compare the vibroacoustic response of a rectangular, thin plate, using the two excitations. A numerical study is made, using a modal expansion to describe the vibrations of the plate. Two excitations are alternately applied. The diffuse field excitation is obtained through the standard summation of plane waves, and the turbulent boundary layer excitation is based on Corcos’ model with Davies’ approximation. In this paper the two approaches are compared, particularly concerning the physical mechanisims producing vibration and noise. An equivalent insertion loss is defined when a turbulent boundary layer is used. One can see that the insertion loss obtained with diffuse field excitation is different to the insertion loss obtained with a turbulent boundary layer excitation, even if the insertion loss curve shapes are quite similar particularly at and above the critical frequency fc. Another important result is that the influence of the plate structural damping varies from one case to the other below fc. Thus the transmission mechanisms probably significantly differ. One can then conclude that using the real excitation is compulsory to make precise assessment of interior noise due to turbulent boundary layer excitation below fc. Nevertheless this result should be confirmed by tests and studies on more realistic configurations.