Determining the strength of rotating broadband sources in ducts by inverse methods
Determining the strength of rotating broadband sources in ducts by inverse methods
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DOI：
10.1016/j.jsv.2006.01.031
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发表时间：
2006-08
影响因子：
4.7
通讯作者：
Christopher Lowis;P. Joseph
中科院分区：
文献类型：
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作者：
Christopher Lowis;P. Joseph
航空发动机宽带风扇噪声是飞机造成的社区噪声暴露的主要原因。目前认为，主要的宽带噪声机制是由于转子与定子的湍流尾流的相互作用以及转子叶片上的湍流边界层与其后缘的相互作用所致。目前还没有测量技术可以对基于转子的宽带噪声源进行定位和量化。本文提出了一种反演技术，利用管道壁上的压力测量来估计管道转子上的宽带声源强度分布。结果表明，管道中声源的旋转妨碍了标准声学反演技术的使用。这里提出了一种新技术，用于反转旋转宽带源的强度，该技术利用新的格林函数，考虑到源旋转的影响。新的格林函数与模态分解技术一起使用，以消除源旋转的影响，从而允许估计旋转参考系中基于转子的源强度。结果表明，应用该技术后传感器测得的压力与与转子以相同速度旋转的传感器测得的压力相同。给出了数值模拟的结果来研究反演技术的分辨率极限。方位分辨率极限，即测量技术区分相邻叶片上的源的能力，被证明随着旋转速度的增加而提高。为了提高反演技术的鲁棒性，做出了简化的假设，即假定不同叶片上的源是相同的。还表明，随着转子和传感器之间的轴向间距减小，反演过程的准确性和鲁棒性得到提高。仿真结果表明，对于以 Mt=0.5 的叶尖马赫数旋转的 26 叶片风扇，当在距转子约 0.1 声波波长处进行测量时，可以以可接受的稳健性和约 1dB 的精度来估计空气动力源强度。
Aeroengine broadband fan noise is a major contributor to the community noise exposure from aircraft. It is currently believed that the dominant broadband noise mechanisms are due to interaction of the turbulent wake from the rotor with the stator, and interaction of the turbulent boundary layers on the rotor blades with their trailing edges. Currently there are no measurement techniques that allow the localisation and quantification of rotor-based broadband noise sources. This paper presents an inversion technique for estimating the broadband acoustic source strength distribution over a ducted rotor using pressure measurements made at the duct wall. It is shown that the rotation of acoustic sources in a duct prevents the use of standard acoustic inversion techniques. A new technique is presented here for inverting the strength of rotating broadband sources that makes use of a new Green function taking into account the effect of source rotation. The new Green function is used together with a modal decomposition technique to remove the effect of source rotation, thereby allowing an estimation of the rotor-based source strengths in the rotating reference frame. It is shown that the pressure measured at the sensors after application of this technique is identical to that measured by sensors rotating at the same speed as the rotor. Results from numerical simulations are presented to investigate the resolution limits of the inversion technique. The azimuthal resolution limit, namely the ability of the measurement technique to discriminate between sources on adjacent blades, is shown to improve as the speed of rotation increases. To improve the robustness of the inversion technique, a simplifying assumption is made whereby the sources on different blades are assumed to be identical. It is also shown that the accuracy and robustness of the inversion procedure improve as the axial separation between the rotor and sensors decreases. Simulation results demonstrate that for a 26-bladed fan, rotating with a blade tip Mach number of Mt=0.5, the aerodynamic source strengths can be estimated with acceptable robustness and approximately 1dB accuracy, when measurements are made approximately 0.1 acoustic wavelengths from the rotor.