Chao Wang, Qiang Peng, Qian Wen «Characterisation of three dimensional cavity noise in moderate Reynold number» Тезисы докладов Шестой открытой Всероссийской (XVIII научно-технической) конференции по аэроакустике (22–27 сентября 2019 г.), с. 217-222 (2019)

Chen Bao, Bao Anyu, Zhou Guocheng «Wind tunnel test technologies investigation of civil transport airframe/jet noise installation» Тезисы докладов Шестой открытой Всероссийской (XVIII научно-технической) конференции по аэроакустике (22–27 сентября 2019 г.), с. 77-79 (2019)

Airframe/jet installation noise is one of the main noise sources of civil aircraft. In order to reduce the noise of civil aircraft and acquire the overall noise characteristics of civil aircraft, it is necessary to acquire the sound pressure level, frequency spectrum characteristics of the airframe/jet installation noise and the effect rules of the relative position in the wind tunnel. In order to study the mechanism and characteristics of airframe/jet installation noise in aeroacoustic wind tunnel, the experimental method of airframe/jet installation noise in 0.5m aeroacoustic wind tunnel of AVIC ARI is studied in this paper. The nozzle noise simulation setup, wing support device and directivity measurement array are designed, and the experiment system is formed. The nozzle simulation setup can be installed with variable diameter nozzle, the position of the wing can be changed in the direction of axis and height. The diameter of the microphone phase array is lm, the number of microphones is 63, the distance from the nozzle center is 1.2m, the radius of the directivity arc is 1.8m, the directivity angle is 45–135 degrees and 225–315 degrees respectively with the interval 9 degress between microphones. Microphones are equipped with windproof balls. Secondly, the NACA0012 wing with 127mm chord length and the nozzle with the diameter D 25.4mm are tested in 0.5m aeroacoustic wind tunnel. The noise characteristics of airframe/jet installation effect were studied experimentally. The jet Mach number was 0.9, the free flow Mach number was 0.2, and the height and axial relative position ranges were 0.5D and 1.0D, respectively. The experiment data were obtained. Finally, based on the experiment data, the influence of the relative position of airframe and jet on the noise was analyzed and discussed. The results show that the existence of wing makes the azimuth angle 90 degree point noise. Acoustic pressure level increases to 5 dB, the change of relative position in the axis has little effect on directivity, and the noise pressure level increases when the wing is close to the nozzle in the height direction.

Zhang Jun, Wang Xunnian, Chen Zhengwu, Zhang Junlong «A study of the localization and quantification of noise sources using an inflow-speaker calibration» Тезисы докладов Шестой открытой Всероссийской (XVIII научно-технической) конференции по аэроакустике (22–27 сентября 2019 г.), с. 64 (2019)

Aeroacoustic tests are preferred to be performed in open-jet wind tunnels. Shear layer causes phase and amplitude distortion of sound during the propagation of sound from the inside to the outside of open-jet flow. The phase and amplitude of sound must be corrected for accurate localization and quantification of sound sources using a microphone array. In this study, a new method of correcting shear-layer effect is proposed. The transfer function of sound is obtained using an inflow-speaker calibration. The cross- spectrum matrix of the measured sound pressure is then corrected according to the transfer function, which is later used as an input for the noise map generation using beamforming. Experiment studies were performed in the 0.55m by 0.4m aeroacoustic wind tunnel in China Aerodynamics Research and Development Center. A comparison study was made between the present method and the traditional shear-layer correction method, e.g., Amiet’s method. More accurate estimation of the location and amplitude of noise source were obtained using the proposed method.

Shakhtarin B.I., Chudnikov V.V., Dyabirov R.M. «Methods of frequency synchronization of OFDM signals in an underwater acoustic channel» Вестник Московского государственного технического университета имени Н.Э. Баумана (МГТУ). Серия: Приборостроение, № 4, с. 62-70 (2019)

Application of signals with orthogonal frequency division multiplexing in underwater communication systems allows efficient use of the information transfer channel bandwidth and thereby increase the carrying capacity of the system. Among the main distinguishing features of the underwater channel there are the relatively low speed of sound propagation in water, multiple reflections from the water surface and the bottom of the reservoir and the Doppler effect, which leads to compression/stretching of the signal in time. The model of the underwater acoustic channel was developed on the assumption that the signal at the receiver input is a superposition of the signals which are copies of the transmitted signal, but passed through different paths from the transmitter. Each signal has its own amplitude, time delay and degree of compression/stretching in time. For correct demodulation of the orthogonal frequency division of the channel-signal, the receiver must first perform time and frequency synchronization. Time synchronization is performed to determine the beginning of the packet and the symbols' boundaries, and frequency synchronization is necessary for matching the receiver and transmitter sampling frequency to eliminate interchannel interference.For frequency synchronization in a hydroacoustic channel of orthogonal frequency division type, either the preambles invariant to Doppler effect or pilot components of the channel of the orthogonal frequency division type are used. The method based on the synchronization preamble and on a bank of matched filters uses a non-invariant to the Doppler effect preamble at the beginning of the packet. Each filter is matched with a preamble having compression/stretching in time. The autocorrelation method assumes that two identical symbols are included in the transmitted data block for signals with orthogonal frequency division multiplexing, which are used to estimate the scale of signal stretching/compression. The conclusions on the advantages of using orthogonal frequency division multiplexing in an underwater acoustic channel are given.