The experimental reproduction in laboratory conditions of random pressure fields with prescribed statistical properties is a subject of considerable interest within several areas. In the aeronautical and aerospace industries, there is a timely interest in the laboratory simulation of random loads over components subjected to high fluctuating pressure levels. It is then useful to investigate how a laboratory system could synthesise propeller-induced noise excitations. In particular, a grazing incident plane wave of random phase and amplitude has been modelled to evaluate the dynamic response and the sonic fatigue of aeronautical structures. The facilities that are currently used for such an analysis are Acoustic Progressive Wave Tubes (APWT), that are costly to use and time-consuming, and are not able to reconstruct the detailed spatial correlation patterns associated to the simulated random excitations. The aeronautical industry is also concerned with cabin noise problems and their impact on discomfort and the integrity of the electronic equipment. The noise induced by Turbulent Boundary Layer (TBL) pressure fluctuations developed over the fuselage of well-streamlined aircraft is important during cruise conditions.
Panel excited by a ideal TBL excitation (left) and electro-acoustic device for the synthesis of the desired field
Using this methodology, the statistical properties of the two types of wall-pressure excitations previously outlined -a grazing plane wave, and a TBL pressure field- has been simulated with a near-field array of 4X4 loudspeakers situated in a semi-anechoic chamber. The investigations carried out with these particular examples have shown the capabilities and limitations of this arrangement to reproduce the statistics of the particular pressure fields. However, this investigation can be extended to other real-world acoustic or vibration environments. Moreover, adaptive acoustic controller can be developed to generate the driving signals tailored to experimental field measurements and to provide design shaping filters, the output of which are the simulated spectra.
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| Spatial correlation functions (right) at 200 Hz and 600 Hz when assuming a perfect reproduction of a TBL pressure field -top-, predicted from the transfer functions measurements -middle- and generated experimentally by the electro-acoustic device with 4 x 4 loudspeakers -bottom- | |
