A reciprocity technique for the characterisation of sound transmission into aircraft fuselages

Mason, James Meredith (1990) A reciprocity technique for the characterisation of sound transmission into aircraft fuselages. University of Southampton, Doctoral Thesis.

Abstract

Experimental determination of the sound insulation of propfan aircraft fuselage structures is problematic. The use of full-scale flight tests to investigate and optimise sidewall design is expensive, while the use of simplified excitation tests is questionable, due to the complicated nature of propeller sound fields and their interaction with the fuselage. This thesis describes the development and evaluation of a new experimental reciprocity technique for calibrating a fuselage as a transmitter of pressure acting on the external surface to the interior: it is based upon the use of a transducer which measures the volume velocity of the vibrating fuselage surface. The data generated may be combined with any impinging sound field to obtain a prediction of cabin sound pressure level. In the first instance, the technique is validated for sound transmission through flat panels into a rigid walled box and the results presented demonstrate the validity of the approach. Tests are then conducted on a set of four quarter-scale `green' fuselage model configurations, constructed to investigate the influence of ring frame bending-stiffness, stringers and floor on airborne sound transmission. Interior noise predictions are obtained for plane wave excitation and a representation of propeller sound field excitation. The important features relating to correct representation of the excitation field and the fuselage structure are isolated, within the scope of the models evaluated. In addition, a statistical perturbation technique is described which demonstrates confidence in the predictions. The technique is recommended for evaluation on a full size airframe.

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