{'fraction_non_alphanumeric': 0.013900955690703735, 'fraction_numerical': 0.006081668114682885, 'mean_word_length': 5.3646408839779, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
ON EFFICIENCY OF SOME METHODS FOR DETERMINING THE AZIMUTHAL STRUCTURE OF NOISE IN CYLINDRICAL DUCT

The determination of azimuthal sound modes propagating in a cylindrical duct is considered based on the results of noise measurements on experimental setup with a duct diameter of 1.8 m, which corresponds to the air intake of aircraft engine. The experiments were carried out in PNRPU anechoic chamber. Spinning modes were generated by a circular array of 40 acoustic drivers. Noise in duct was recorded with circular array of 100 microphones with optimized arrangement to reach maximum dynamic range. The following methods for determining the azimuthal structure of noise were compared: modal decomposition method, cross-correlation with a reference channel method; least-squares method. The mathematical foundations and specifics of these methods are briefly outlined. According to the results of the azimuthal structure extraction, it was found that the least-squares method provides the best agreement between the generated and extracted modes and the distribution of the computed and experimental values of acoustic pressures on microphone array.