Coherent sound source localization of an electric ducted fan by SODIX

Recent developments in the source localization method (SOurce DIrectivity modelling in the cross-spectral matriX, SODIX) enable the determination of complex amplitudes and directivity of distributed partially coherent sources in static engine noise tests. In this paper, the method was successfully employed in the tonal noise study of an electric ducted fan test. High-quality test data were acquired by a densely distributed microphone line array, and the frequency fluctuations of the tones at each harmonic order were examined. The directivities results indicated that the coherence between fan inlet and outlet sound sources significantly affected the far-field noise radiation characteristics. For comparision, two versions of SODIX were used: one was SODIX-classic with the assumptions of incoherent sources and real valued source amplitudes, and the other was SODIX-bomp, which used the Block Orthogonal Matching Pursuit (BOMP) algorithm with the assumptions of partially coherent sources and complex valued source amplitudes. SODIX-bomp achieved cleaner and more reliable sound source localization results. Through regional integration, the fan inlet and outlet sound sources were reasonably decomposed, and the reconstructed far-field directivities were consistent with the experimental results. In summary, coherence must be given serious attention in noise characteristic studies for electric ducted fans, and the SODIX algorithm that takes coherence into account represents a promising method.