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. An acoustic liner development and optimization process was conceived and employed to achieve and demonstrate an improved broadband liner design concept. A series of increasing technology readiness level liner studies were conducted to enhance the optimization methodology while validating the concept. This progression spanned several NASA Aeronautics Research Mission Directorate programs/projects due to its relevance. This article reviews the development and evaluation process of the multi-degree-of-freedom liner technology concept from formation through simple experimental models to a flight test over an approximate 10-year period, focusing on the discrete tests comprising the development.

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。构想并采用声学衬垫开发和优化过程来实现和展示改进的宽带衬垫设计概念。进行了一系列提高技术准备水平的班轮研究，以在验证概念的同时增强优化方法。由于其相关性，这一进展跨越了多个 NASA 航空研究任务理事会计划/项目。本文回顾了多自由度班轮技术概念的开发和评估过程，从形成到简单的实验模型，再到大约 10 年的飞行测试，重点关注包括开发的离散测试。