Проводится исследование акустических характеристик образцов звукопоглощающих конструкций (ЗПК) в ин-терферометрах с разным диаметром поперечного сечения канала с целью отработки методики надежной идентифика-ции акустических характеристик ЗПК при учете распространения в канале азимутальной моды для дальнейшего приме-нения методики к измерению крупногабаритной ЗПК портативным интерферометром. Основу проверки составляет по-ложение о независимости импеданса локально реагирующих ЗПК от диаметра образца при нормальном падении волн.Кратко описаны основы определения импеданса образцов ЗПК по измерениям двумя и четырьмя микрофонами в канале интерферометра. Представлена конструкция нового интерферометра с диаметром канала 50 мм. Исследован частотный диапазон работы созданного интерферометра. Разработаны и созданы однослойные и двухслойные образ-цы ЗПК диаметром 30 и 50 мм. Обработка результатов измерений выполнялась с применением метода передаточной функции на основе двух микрофонов и метода модальной декомпозиции на основе четырех микрофонов. Для всех ис-следованных образцов ЗПК наблюдается хорошее качественное согласование импедансов между соответствующими образцами диаметром 30 и 50 мм. Также в большей части частотного диапазона наблюдается хорошее количественное совпадение. Некоторые количественные расхождения объясняются трудностью воспроизводства абсолютной одинако-вости условий проведения эксперимента в двух разных интерферометрах.Ключевые слова: авиационный двигатель, шум вентилятора, звукопоглощающие конструкции, импеданс, ин-терферометр с нормальным падением волн, метод модальной декомпозиции, метод передаточной функции.
INVESTIGATION OF ACOUSTIC CHARACTERISTICS OF LINER SAMPLES IN INTERFEROMETERS WITH DIFFERENT DUCT DIAMETERThe investigation of acoustic characteristic of sound-absorbing liner samples in normal incidence interferometers with different diameters of a duct is carried out. The object of the investigation is the test of the technique for reliable identification of the liner acoustic characteristics, taking into account the propagation of azimuthal mode in the duct, for further application of the technique to measuring the large-scale liners by portable interferometer. The basis of the verification is the independence of the impedance of locally reacting liner on the sample diameter when the normal waves incident.The fundamentals of the determination of the liner sample impedance based on 2-and 4-microphones measurements in the interferometer are briefly described. The design of a new interferometer with a duct diameter of 50 mm is presented. The frequency range of the created interferometer is investigated. Single-layer and double-layer liner samples with diameter of 30 and 50 mm were developed and produced by additive technology. The processing of the measurement results was carried out using the transfer function method based on 2 microphones, and the modal decomposition method based on 4 microphones. For all investigated liner samples, a good qualitative matching of the impedances between the co...
The present work details a new approach to the study of GTU rotor vibrations, based on the solution of a related dynamic problem for the «gas – dynamic flow – deformable structure» sys-tem. The modern tendency to increase an aggregates power with a simultaneous decrease stiffness results in new phenomenons that affected a rotor vibration state. The compressor rotor model with a labyrinth seal is considered. ANSYS software product is used. The calculations were carried out on a high-performance computer complex PNRPU. The performed calculations showed a qualitative and quantitative effect of a gas-dynamic gap on the rotor dynamics. A 2FSI calculations series was performed to study the influence of geometric, kinematic and gas-dynamic parameters on the rotor dynamic state. A pressure fluctuations spectral analysis in the gas-dynamic gap and displacements has been carried out. The obtained spectrograms pro-cessing it possible to plot amplitudes and frequencies dependences of resonant pressure oscil-lations over an initial pressure in the gas-dynamic gap. It was found that the initial pressure in a gas-dynamic gap has the greatest influence. A rotor and gas oscillations resonant frequency was found, which corresponds to a change in the shaft axis spatial position. The «gas – struc-ture» system resonant frequencies were obtained for models differing in mass and stiffness. A decrease in an elasticity modulus of the structure led to a decrease in the maximum pressure fluctuations amplitude, while a decrease in mass led to its increase. For the base model and the model with lower rigidity, the resonant pressure oscillations frequency depends on the initial pressure value according to a law close to linear, while for the model with a lower mass, the dependence has a pronounced non-linear character.
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