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New Numerical Procedure for Impedance Eduction in Ducts Containing Mean Flow

机译：包含平均流的管道中阻抗降低的新数值程序

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摘要

A new impedance eduction method is presented and validated against a benchmark method, and the effects of measurement uncertainty errors on the impedances educed with this new method are assessed. Unique features of the new method include the following: 1) the upstream and downstream boundary conditions contain higher-order duct modes, 2) the impedance spectra of unique nonuniform test liners on opposite walls may be educed simultaneously, and 3) the measured data for the impedance eduction are acquired only at the source and duct termination planes. The validation exercise is performed with a rigid-wall insert and a conventional liner over a range of frequencies and flow Mach numbers in the NASA Langley Research Center's grazing flow impedance tube. The primary conclusions of the study are that the impedance spectra of the rigid-wall insert and the conventional liner that were educed from the new method are in very good agreement with those that were educed by using the benchmark method. However, the effects of measurement uncertainty on the educed impedance are greater at the lower frequencies and the higher Mach numbers for the new method. All indications are that this occurs because the new method 1) uses significantly less data to perform the impedance eduction than the benchmark and 2) is currently based on a rather crude approximation to the measured pressure gradient, which is more sensitive to the refractive effects of the boundary layer than the measured lower-wall pressure that is required in the benchmark method.
机译：提出了一种新的阻抗减小方法，并针对基准方法进行了验证，并评估了测量不确定度误差对该方法产生的阻抗的影响。新方法的独特功能包括：1）上游和下游边界条件包含高阶管道模式； 2）可以同时导出相对壁上独特的非均匀测试衬管的阻抗谱，以及3）仅在源极和管道终端平面上获得阻抗辐射。验证工作是通过在美国宇航局兰利研究中心的掠流阻抗管中的频率和流动马赫数范围内的刚性壁插入物和常规衬里进行的。该研究的主要结论是，用新方法测得的刚性壁插入件和常规衬套的阻抗谱与使用基准法测得的阻抗谱非常吻合。但是，对于新方法，在较低频率和较高马赫数下，测量不确定度对感应阻抗的影响更大。所有迹象表明发生这种情况是因为新方法（1）使用的数据比基准测试少得多，并且2）当前是基于对测得的压力梯度的粗略近似，这对Pd的折射效应更为敏感。边界层比基准方法中测得的下壁压力要高。

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