Experimental reproduction of random pressure fields in laboratory conditions

Abstract

The design and the physical implementation of an experimental set-up are discussed for the off-line reproduction of random wall-pressure fluctuations with given spatial correlation characteristics. This approach could provide a cost-effective laboratory method of both reducing the variability of low frequency sound transmission measurements as well as measuring the boundary layer noise transmitted through aircraft fuselage structures. Three different types of random excitations are considered, namely an acoustic diffuse field, a turbulent boundary layer excitation and an acoustic progressive wave at grazing incidence angle. The corresponding excitations are generated in a semi-anechoic chamber using a near-field array of 4×4 loudspeakers optimally driven and located above a set of 13×16 microphones. The microphones are positioned a short distance apart from an aluminum test panel. The optimal driving signals are determined from acoustic transfer functions measurements between the grid of microphones and the array of loudspeakers. Given this number of loudspeakers, a reasonable reproduction of the boundary-layer excitation is achieved up to about 200 Hz and a good approximation of both the acoustic diffuse field and the progressive wave is obtained over the frequency range of interest, i.e. up to about 700 Hz. [Work supported by ANVAR.]