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Effects of Liner Length and Attenuation on NASA Langley Impedance Eduction

机译：衬里长度与衰减对NASA Langley阻抗的影响

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This study explores the effects of liner length and attenuation on the CHE (convected Helmholtz equation) impedance eduction method, in which the surface impedance of an acoustic liner is inferred through an iterative process based on repeated solutions to the convected Helmholtz equation. Wire mesh-over-honeycomb and perforate-over-honeycomb acoustic liners are tested in the NASA Langley Grazing Flow Impedance Tube, and the resultant data are processed using two impedance eduction methods. The first is the CHE method, and the second is a direct method (labeled the KT method) that uses the Kumaresan and Tufts algorithm to compute the impedance directly. The CHE method has been extensively used for acoustic liner evaluation, but experiences anomalous behavior under some test conditions. It is postulated that the anomalies are related to the liner length and/or attenuation. Since the KT method only employs data measured over the length of the liner, it is expected to be unaffected by liner length. A comparison of results achieved with the two impedance eduction methods is used to explore the interactive effects of liner length and attenuation on the CHE impedance eduction method.
机译：该研究探讨了衬里长度和衰减对Che（对象Helmholtz方程）阻抗的影响，其中通过基于对对象的Helmholtz方程的重复解决方案的迭代过程推断出声学衬里的表面阻抗。在NASA Langley放牧流量阻抗管中测试丝网过度蜂窝和穿孔过度蜂窝声衬里，并使用两种阻抗进程方法处理所得数据。第一个是CHE方法，第二个是一种使用Kumaresan和TUFTS算法直接计算阻抗的直接方法（标记为KT方法）。 CHE方法已广泛用于声学衬里评估，但在某些测试条件下经历异常行为。假设异常与衬里长度和/或衰减相关。由于KT方法仅采用在衬里的长度上测量的数据，因此预计将不受衬垫长度的影响。通过两种阻抗进展方法实现的结果进行了比较，用于探讨衬里长度和衰减对CHE阻抗的互动的互动影响。

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