Interior noise of an aircraft fuselage: Dynamics and structural acoustics with experimentation

The area of interior noise is of growing interest to the aircraft industry due to recent trends associated with increasing passenger comfort. In an effort to understand the physics of the problem, highly spatially sampled surface motion and interior acoustic measurements of a business jet fuselage section under point excitation were made over a band from 10 to 1000 Hz. Both the cylindrical shell and endcaps were measured using laser Doppler vibrometry and the associated coupling of these structural modes to interior pressure levels is observed and discussed. Superimposed on this interior response are the normal cavity modes of the interior which set up due to the quasirigid boundaries. Localization of the fulselage vibrations with the associated passbands and stop bands are found due to the pseudo- periodic nature of the internal structure of the fulselage. These structural acoustic attributes may be exploited to reduce the interior acoustic levels. a)Also at Sachs/Freeman Associates, Inc., 1401 McCormick Dr., Landover, MD 20785.