{"title":"撞击喷流产生的声调:层流边界层与高扰动喷嘴出口边界层之间的差异","authors":"Mathieu Varé, C. Bogey","doi":"10.1177/1475472x241230647","DOIUrl":null,"url":null,"abstract":"The differences between the acoustic tones generated by impinging jets with laminar and highly-disturbed nozzle-exit boundary layers are investigated. For that, jets at Mach numbers between 0.6 and 1.3 impinging on a flat plate at a distance of 8 nozzle radii from the nozzle exit are computed using large-eddy simulations. The amplitudes of the tones generated by the jets through feedback loops establishing between the nozzle and the plate are found to be significantly affected by the exit turbulent disturbances. In the present study, overall, they are lower for the initially laminar jets than for the initially disturbed ones. The level decrease varies from a few dB up to 15 dB, depending on the tones, which can change the frequencies of the dominant tones and the numbers and azimuthal structures of their associated feedback modes. For Mach numbers 0.75 and 0.8, for instance, the dominant tone frequencies are approximately two times lower for the initially laminar jets than for the other ones, yielding a better agreement with experiments of the literature in the former case. For a Mach number of 1.1, as a second example, the dominant tone is associated with the axisymmetric third feedback mode in the laminar case but with the helical fifth feedback mode in the disturbed case. The differences in the tone amplitude are finally discussed by estimating the power gains of the shear-layer instability waves between the nozzle and the plate using linear stability analysis for the axisymmetric mode. 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The amplitudes of the tones generated by the jets through feedback loops establishing between the nozzle and the plate are found to be significantly affected by the exit turbulent disturbances. In the present study, overall, they are lower for the initially laminar jets than for the initially disturbed ones. The level decrease varies from a few dB up to 15 dB, depending on the tones, which can change the frequencies of the dominant tones and the numbers and azimuthal structures of their associated feedback modes. For Mach numbers 0.75 and 0.8, for instance, the dominant tone frequencies are approximately two times lower for the initially laminar jets than for the other ones, yielding a better agreement with experiments of the literature in the former case. For a Mach number of 1.1, as a second example, the dominant tone is associated with the axisymmetric third feedback mode in the laminar case but with the helical fifth feedback mode in the disturbed case. 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引用次数: 1
摘要
研究了具有层流边界层和高扰动喷嘴出口边界层的撞击喷流所产生的声调之间的差异。为此,使用大涡流模拟计算了马赫数在 0.6 和 1.3 之间的喷流撞击到距离喷嘴出口 8 个喷嘴半径处的平板上的情况。研究发现,喷流通过在喷嘴和平板之间建立的反馈回路产生的音调振幅受到出口湍流扰动的显著影响。在本研究中,总体而言,初始层流喷流的音调低于初始扰动喷流。电平降低幅度从几 dB 到 15 dB 不等,取决于音调,这可能会改变主要音调的频率及其相关反馈模式的数量和方位角结构。例如,在马赫数为 0.75 和 0.8 时,初始层流喷流的主音频率比其他喷流的主音频率低约两倍,前者与文献中的实验结果更为一致。第二个例子是马赫数为 1.1 时,层流情况下的主音与轴对称第三反馈模式有关,而扰动情况下的主音与螺旋第五反馈模式有关。通过对轴对称模式进行线性稳定性分析,估算喷嘴和板之间剪切层不稳定波的功率增益,最终讨论了音调振幅的差异。在大多数情况下,在特定声调的频率下,增益越高,声调越强。
Acoustic tones generated by impinging jets: Differences between laminar and highly-disturbed nozzle-exit boundary layers
The differences between the acoustic tones generated by impinging jets with laminar and highly-disturbed nozzle-exit boundary layers are investigated. For that, jets at Mach numbers between 0.6 and 1.3 impinging on a flat plate at a distance of 8 nozzle radii from the nozzle exit are computed using large-eddy simulations. The amplitudes of the tones generated by the jets through feedback loops establishing between the nozzle and the plate are found to be significantly affected by the exit turbulent disturbances. In the present study, overall, they are lower for the initially laminar jets than for the initially disturbed ones. The level decrease varies from a few dB up to 15 dB, depending on the tones, which can change the frequencies of the dominant tones and the numbers and azimuthal structures of their associated feedback modes. For Mach numbers 0.75 and 0.8, for instance, the dominant tone frequencies are approximately two times lower for the initially laminar jets than for the other ones, yielding a better agreement with experiments of the literature in the former case. For a Mach number of 1.1, as a second example, the dominant tone is associated with the axisymmetric third feedback mode in the laminar case but with the helical fifth feedback mode in the disturbed case. The differences in the tone amplitude are finally discussed by estimating the power gains of the shear-layer instability waves between the nozzle and the plate using linear stability analysis for the axisymmetric mode. In most cases, at the frequency of a specific tone, the higher the gain, the stronger the acoustic tone.
期刊介绍:
International Journal of Aeroacoustics is a peer-reviewed journal publishing developments in all areas of fundamental and applied aeroacoustics. Fundamental topics include advances in understanding aeroacoustics phenomena; applied topics include all aspects of civil and military aircraft, automobile and high speed train aeroacoustics, and the impact of acoustics on structures. As well as original contributions, state of the art reviews and surveys will be published.
Subtopics include, among others, jet mixing noise; screech tones; broadband shock associated noise and methods for suppression; the near-ground acoustic environment of Short Take-Off and Vertical Landing (STOVL) aircraft; weapons bay aeroacoustics, cavity acoustics, closed-loop feedback control of aeroacoustic phenomena; computational aeroacoustics including high fidelity numerical simulations, and analytical acoustics.