CHARACTERISATION OF SPECTRAL LINES: APPLICATION TO AIRBORNE MEASUREMENTS OF TWO GENERATING SETS

This paper shows the complementarity of two methods applied to the analysis of an airborne measurement in the open with two generating sets running. The aim is to identify and characterise the spectral lines. The LABRADOR method was originally developed in order to separate broadband sources in a mixed output. The broadband feature of the issue has to be treated with a narrowband approach in order to keep good coherence assessment between the inputs and the output. This confers the method, the capability to treat both broadband and narrowband phenomena. The LABRADOR method allows to identify the mechanisms corresponding to each line (thanks to a set of microphones located close to the suspected sources), but the accuracy about the frequency is the resolution of the Fourier analysis. So, using the AutoCoherent Spectrum method (ACS) which can be regarded as a single-channel cross-spectrum, allows to characterise the lines with much more accuracy and this way to identify easily the harmonic families.