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Impedance and attenuation measurements of acoustic absorbers in a hot environment

机译：炎热环境中吸声器的阻抗和衰减测量

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New manufacturing processes and/or new design concepts of acoustic liners in aeroengines require adequate adapted design models. The availability of models is the prerequisite to design and optimize novel acoustic liners to the targeted acoustic properties. Within the present manuscript the procedure to generate sufficient data to validate such models for an acoustic liner to work in a hot environment with flow is described. A novel slit absorber is investigated and compared to a conventional SDOF. Both feature a micro-perforate facing sheet. Measurements with a hand held portable impedance tube are used to determine the acoustic properties without flow at ambient temperature. This relatively quick procedure allows determining the effective acoustic porosity and other parameters, and also provides means for quality control. It demonstrates an excellent manufacturing repeatability of the absorber samples. The temperature and flow effect on the acoustic impedance is further investigated in the DLR HAT facility. The HAT measurements cover a range temperatures and Mach numbers, which is relevant for the hot exhaust of an aero engine. The experimental data (insertion loss and impedance) are used for comparison to model predictions with a proprietary in house model. Finally it is show that the novel slit absorber is able to achieve almost the same peak attenuation at a 50% lower design frequency than a SDOF of the same cell depth.
机译：航空发动机中的隔音衬里的新制造工艺和/或新设计概念需要适当的适应性设计模型。模型的可用性是根据目标声学特性设计和优化新型声学衬管的前提。在本手稿中，描述了生成足够数据以验证用于声学衬管以在具有流动的高温环境中工作的模型的过程。研究了一种新型狭缝吸收器，并将其与传统的SDOF进行了比较。两者均具有微孔饰面片材。使用手持式便携式阻抗管进行的测量可确定声学特性，在环境温度下无流动。该相对快速的过程允许确定有效的声孔隙率和其他参数，并且还提供了用于质量控制的手段。它证明了吸收体样品具有极好的制造可重复性。在DLR HAT设备中进一步研究了温度和流量对声阻抗的影响。 HAT测量涵盖范围温度和马赫数，这与航空发动机的热排气有关。实验数据（插入损耗和阻抗）用于与内部专有模型的模型预测进行比较。最终表明，新型缝隙吸收器能够以比相同单元深度的SDOF低50％的设计频率实现几乎相同的峰值衰减。

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