Fan Broadband Noise Localization and Mode Identification Technology in Turbofan Engine

Microphone array measurement technology is widely used for aeroacoustic measurement, because it has the advantages of being far away from strong mutual interference regions, which can avoid intrusion of the flow field, increasing the size can improve the spatial resolution and increasing the number of microphones can promote dynamic range. As the ducting ratio of civil aeroengine increases, the proportion of fan noise is increasing. In the fan noise, the development of tone noise reduction technology is more mature which makes the problem of broadband noise more prominent. However, the mechanism of broadband noise generation is complicated and signal-to-noise ratio is relatively poor, which make it difficult to control broadband noise. Efficient and accurate in-duct fan broadband sound source localization and mode identification can be realized by arranging a ring or multi-ring microphone array around the duct, which can greatly assist the fan broadband noise reduction technology. This paper summarizes the in-duct rotating broadband noise localization and mode identification technology developed in foreign countries in recent years, namely the in-duct rotating beamforming and the mode beamforming, which use the experimental data provided by the University of São Paulo in Brazil for code verification and compare the calculation results with conventional beamforming and mode decomposition. The results show that the in-duct rotating beamforming has higher source resolution and dynamic range. The mode beamforming with multi-ring array has better radial modal identification capability than the mode decomposition. Finally, the advantages and disadvantages of the new technology and the future improvement direction are expounded.