Spinning mode analysis of the acoustic field generated by a turboshaft engine
Spinning mode analysis of the acoustic field generated by a turboshaft engine
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DOI：
10.2514/3.46287
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发表时间：
1992-11
影响因子：
2.2
通讯作者：
D. Blacodon;S. Lewy
中科院分区：
文献类型：
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作者：
D. Blacodon;S. Lewy
管道声场的旋转模式分析是推进对涡轮风扇或涡轮轴发动机噪声源的理解的有力手段，也是预测入口或喷嘴辐射的远场方向性所需的主要信息。在透博梅卡 TM 333 涡轮轴发动机的喷嘴横截面中使用圆形固定麦克风阵列进行了测试，以确定其声场的模态特性。数据处理的主要困难来自于由于内部流动非常湍流而导致的高背景噪声。因此，基于互谱矩阵的角度傅立叶变换的传统方法可能是不够的。通过数值模拟讨论和验证了一些改进，例如使用三信号相干技术来降低输出噪声。通过减少由于统计平均值的数量有限而导致的估计偏差，可以获得进一步的增益。最后一节给出了几个频率下的实验 TM 333 波数谱，对应于宽带燃烧噪声以及高压涡轮和自由涡轮发出的音调。通过考虑喷嘴截止特性和跨音速转子的辐射机制来解释观察到的旋转模式。
The spinning mode analysis of a ducted acoustic field is a powerful means for advancing the understanding of noise sources in turbofan or turboshaft engines, and it is also the main information needed to predict the far-field directivity radiated by the inlet or the nozzle. Tests were made with a circular array of fixed microphones in a nozzle cross section of a Turbomeca TM 333 turboshaft engine to determine the modal characteristics of its acoustic field. The main difficulty in data processing comes from the high background noise due to the very turbulent internal flow. A conventional method based on the angular Fourier transform of the cross-spectral matrix may therefore be inadequate. Several improvements are discussed and validated by numerical simulations, such as the use of a three-signal coherence technique to reduce the output noise. A further gain is achieved by the reduction of the estimate bias due to the finite number of statistical averages. The experimental TM 333 wave-number spectra are presented in the last section at several frequencies, corresponding to the broadband combustion noise and to the tones emitted by the high-pressure turbine and the free turbine. The observed spinning modes are explained by taking into account the nozzle cut-off properties and the radiation mechanisms of transonic rotors.