Авіаційно-космічна техніка та технологія (Aug 2022)
Research of acoustic characteristics of experimental samples of acoustic liners for gas turbine engines7
Abstract
It is shown that the problem of aviation noise affecting the population near airports is still relevant. Pollution from aircraft noise is not a less influential factor than air or water pollution. The international community is paying close attention to tackling aviation noise by introducing requirements and noise limits for aircraft under development or in operation. Among the sources of aircraft noise, one of the main sources that should be singled out - the noise generated by gas turbine engines. Among the sources of noise of gas turbine engines should be noted to highlight the noise of the fan. To reduce the noise level of engines, various methods are used, among which should be noted the use of acoustic liners placed in the nacelles of the engine. To meet modern international requirements, acoustic liners must reduce the noise level in a wide frequency range. It is shown that there are several methods for determining the acoustic characteristics of acoustic liners: the standing wave method, the transfer function method, the reverberation chamber method, and the use of a flow-through acoustic channel. Each of these methods can be used in the stages of development of acoustic liners for gas turbine engines. It is shown that the standing wave method should be used at the initial stage of research, as it allows to determine the most promising acoustic liners for further research. This paper presents the results of research for six prototypes of acoustic liners. The measurement results of the prototypes were compared with the results of the measured design used to reduce the noise of the D-18T engine. Two prototypes should be distinguished among the prototypes. In the designs of the first group, noise reduction in various frequencies was achieved by the effect of viscous friction due to the holes in the filler cells as in porous fiber materials. In the designs of the second group, the expansion of the absorption frequency range was achieved due to the placement of cells with different resonant frequencies. Studies have shown that it is possible to create acoustic liners that absorb noise in a wide frequency range, so a prototype has a sound absorption coefficient of more than 0.8 in the frequency range from 1600 Hz to 3500 Hz.
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