Assessment of a metamaterial-inspired active acoustic liner concept for application to aircraft engine noise reduction

Acoustic liners are a widespread solution for noise mitigation at aircraft engine level, thanks to lightweight and relatively small dimensions for integration within nacelles. Although conventional liners might be designed to target multiple tonal frequencies, their passive principle prevents the adaptation to varying engine speeds and therefore lowers their performance during flight, especially in the take-off and landing phases. We present here a novel concept of active acoustic liner, based on an architectured distribution of electromechanical resonators, aiming at absorbing noise over a broad frequency bandwidth. Integration issues have been taken into account so as to fit to the targeted application to aircraft engines, yielding thickness and weight minimization, with a view to challenging existing passive, frequency-limited, liners. A prototype of the proposed active lining concept has been tested in an industrial Acoustic Flow Duct Facility in the presence of flow. The results show that such a concept is readily surpassing conventional passive liners, both in terms of insertion loss value and frequency bandwidth.