The emphasis on increased turbofan fuel efficiency requires advanced turbofan designs that will integrate higher engine bypass ratios and shorter nacelles. The resulting acoustic signature of these designs will have a more broadband character as well as a smaller available area for liner installation. This two-fold impact compels a need for an improvement in the state of the art in liner technology. Increasing the acoustic absorption efficacy over a broader frequency range is a means to address this need. NASA investigated over-the-rotor acoustic liners for turbofan applications as a potential solution. This type of liner represents a significant advance over traditional liners due to placement in close proximity to the rotor. An advantage of placing treatment in this region is a modification of the acoustic near field, thereby inhibiting noise generation mechanisms. This can result in higher attenuation levels than could be achieved by the conventional sound absorption means. In addition, there is potential to integrate the liner with fan rub-strip and containment components, reducing engine components and thus weight, enabling a systematic enhancement in noise reduction and engine performance. This article reviews the development and evaluation process of three unique over-the-rotor concepts focusing on the discrete tests conducted across the Technology Readiness Level span.

对提高涡轮风扇燃油效率的重视需要先进的涡轮风扇设计，这些设计将集成更高的发动机涵道比和更短的发动机舱。这些设计的最终声学特征将具有更多的宽带特性以及更小的衬垫安装可用区域。这种双重影响迫使需要改进衬里技术的现有技术。在更宽的频率范围内提高吸声效率是满足这一需求的一种手段。NASA 研究了用于涡轮风扇应用的超转子声学衬垫作为潜在的解决方案。由于放置在靠近转子的位置，这种类型的衬管比传统的衬管有了显着的进步。在该区域进行治疗的一个优势是对声学近场的修改，从而抑制噪声产生机制。这会导致比传统吸声装置所能达到的衰减水平更高。此外，还有可能将内衬与风扇摩擦条和密封部件集成在一起，从而减少发动机部件和重量，从而系统地增强降噪和发动机性能。本文回顾了三个独特的转子概念的开发和评估过程，重点是在技术准备水平跨度范围内进行的离散测试。能够系统地增强降噪和发动机性能。本文回顾了三个独特的转子概念的开发和评估过程，重点是在技术准备水平跨度范围内进行的离散测试。能够系统地增强降噪和发动机性能。本文回顾了三个独特的转子概念的开发和评估过程，重点是在技术准备水平跨度范围内进行的离散测试。