Presented here is the development of a predictive model for impedance of single-degree-of-freedom (SDOF) and two-degree-of-freedom (2DOF) acoustic linings that is suitable for the design stage of suppression of inlet noise for turbo-fan engines. It is required that over a probable range of lining physical parameters and operating conditions the impedance spectrum is predicted with accuracy sufficient to support a lining design process and assessment of achievable attenuation. The starting point is a published impedance model for SDOF linings that primarily focuses on the transfer impedance of conventional and micro-perforate face sheets with grazing flow. This is expanded here to include 2DOF linings, introducing new issues related to transfer impedance of the inserted septum. Problems addressed are related to the septum insertion process that can change thickness, hole diameter and open area ratio of the uninstalled septum, and introduce blockage. Required empiricism is discussed and models for face sheet and septum-in-core transfer impedance are derived, applicable to a specific range of sheet thickness, hole diameter, and open area ratio. Manufacturing processes considered are mechanical drilling in the case of the carbon fiber laminate face sheet that is conventional perforate, and laser drilling in the case of the epoxy film micro-perforate septum material. Benchmarking is carried out by comparison of acoustic field predictions, using the proposed lining model in an FEM propagation code, with measured data from a grazing flow duct facility. Test samples include SDOF and 2DOF linings, including cases with three segments, each with distinct physical properties. Example results of comparisons are shown to highlight the fidelity of the impedance model over a frequency range compatible with the grazing flow duct geometry.

这里介绍的是单自由度 (SDOF) 和双自由度 (2DOF) 声学衬里阻抗预测模型的开发，该模型适用于涡轮增压进气噪声抑制设计阶段。风扇引擎。要求在衬砌物理参数和操作条件的可能范围内以足以支持衬砌设计过程和可实现衰减的评估的准确度预测阻抗谱。起点是已发布的单自由度衬里阻抗模型，该模型主要关注具有掠流的传统和微穿孔面板的转移阻抗。这在此处扩展为包括 2DOF 衬里，引入了与插入的隔膜的传输阻抗相关的新问题。解决的问题与隔膜插入过程有关，该过程会改变未安装隔膜的厚度、孔径和开口面积比，并导致堵塞。讨论了所需的经验主义，并推导出了面板和芯中隔片传输阻抗的模型，适用于特定范围的板材厚度、孔径和开口面积比。碳纤维层压面板是常规穿孔时考虑的制造工艺是机械钻孔，而环氧薄膜微穿孔隔膜材料则是激光钻孔。基准测试是通过比较声场预测来进行的，在有限元传播代码中使用建议的衬砌模型，与来自放牧流管道设施的测量数据。测试样品包括单自由度和2自由度衬里，包括具有三个部分的案例，每个部分具有不同的物理特性。比较的示例结果显示了阻抗模型在与掠流管道几何形状兼容的频率范围内的保真度。