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Core Noise Diagnostics of Turbofan Engine Noise Using Correlation and Coherence Functions

机译：基于相关和相干函数的涡扇发动机噪声核心噪声诊断

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Cross-correlation and coherence functions are used to look for periodic acoustic components in turbofan enginencombustor time histories, to investigate direct and indirect combustion noise source separation based on signalnpropagation time delays, and to provide information on combustor acoustics. This investigation uses a combustornpressure sensor and a far-field microphone at 130u0001 to study the change in propagation time to the far field of the directnand indirect combustion noise signal using a generalized cross-correlation function. Results are presented as anfunction of the cutoff frequency of the low-pass filter used to create the generalized cross-correlation function andnengine operating condition. The filtering procedure used produces no phase distortion. As the low-pass-filternfrequency is decreased, the travel time increases. The indirect combustion noise signal travels more slowly, becausenthe entropy in the combustor moves with the flow, which has a low velocity. The indirect combustion noise signalntravels at acoustic velocities after reaching the turbine and being converted into an acoustic signal. The directncombustion noise is always propagating at acoustic velocities. This is in agreement with previous investigations ofndelay times using a cross-spectrum phase-angle method with unfiltered signals that found indirect combustion noisento be in the 0–200 Hz frequency range and the direct combustion noise to be in the 200–400 Hz frequency range.nSimilar results obtained using the cross-spectrum phase-angle method with filtered signals are also shown. Thesenresults show that the low-pass filtering can be used with the cross-correlation function to separate this type ofndependent source and confirm the cross-spectrum results. Although the results are based on a set of static engine testsnconducted for one specific dual-spool turbofan engine configuration, they may lead to a better idea about thenacoustics in the combustor turbine-tailpipe system and may help develop and validate improved reduced-ordernphysics-based methods for predicting turbofan engine core noise.
机译：互相关和相干函数用于查找涡扇发动机燃烧器时间历史中的周期性声学成分，以基于信号传播时间延迟研究直接和间接燃烧噪声源分离，并提供有关燃烧室声学的信息。这项研究使用130u0001处的燃烧压力传感器和远场麦克风，通过广义互相关函数研究了直接和间接燃烧噪声信号向远场传播时间的变化。结果表示为低通滤波器截止频率的函数，该低通滤波器用于创建广义互相关函数和发动机工作条件。使用的滤波过程不会产生相位失真。随着低通滤波器频率的降低，传播时间增加。间接燃烧噪声信号传播得更慢，这是因为燃烧器中的熵随流速而移动，而流速较低。间接燃烧噪声信号在到达涡轮机后以声速传播，并转换为声信号。直接燃烧噪声总是以声速传播。这与以前使用交叉频谱相位角方法对n延迟时间进行的研究一致，其中未滤波的信号发现间接燃烧噪声n处于0–200 Hz频率范围内，而直接燃烧噪声处于200–400 Hz频率范围内.n还显示了使用互谱相位角方法对滤波后的信号获得的相似结果。结果表明，低通滤波可与互相关函数一起使用，以分离这种类型的独立源并确认互谱结果。尽管结果基于针对一种特定的双转子涡扇发动机配置进行的一组静态发动机测试，但它们可能会导致对燃烧室涡轮尾管系统中的声学有更好的了解，并可能有助于开发和验证基于降阶物理的改进方法涡轮风扇发动机核心噪声的预测方法。

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    《Journal of Propulsion and Power》 |2010年第2期|p.303-316|共14页
  • 作者

    Jeffrey Hilton Miles;

  • 作者单位

    Jeffrey Hilton Miles∗NASA John H. Glenn Research Center at Lewis Field, Cleveland, Ohio 44135;

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