Identification of noise sources is a formidable problem in aeroacoustics and is a necessary step to development of methods of noise reduction. Noise mitigation problem is particularly acute for modern aircraft engines, which are major contributors to overall noise of aircraft. To develop effective noise reduction techniques, it is necessary to understand the physics of noise generation mechanisms. One of the methods (Azimuthal Decomposition Technique – ADT), which allows extracting subtle features of noise sources, was elaborated in TsAGI and successfully applied earlier to small-scale jets (Fig. 1a). In laboratory tests ADT is realized by a ring-like 6-microphone array with uniformly distributed microphones located in the acoustic far field of the jet. In the framework of the ongoing activity we have a unique possibility to apply this method to a jet issuing from the real engine (Fig. 1b) and investigate its noise sources. This work is devoted to the modification of ADT to account for both geometrical restrains imposed by the real engine ground test requirements on the location of the microphones and the presence of the hard ground surface.
Fig. 1 – (a) ADT ring array and small nozzle in anechoic chamber AC-2, TsAGI, Moscow; (b) real engine mounted on the open acoustic test rig of Aviadvigatel OJSC, Perm.