Development of acoustic liner in aero engine: a review

Noise reduction for aircraft engine has attracted great concern due to the strict noise control regulation nowadays. Conventional perforated sheet-over-honeycomb acoustic liners have been widely used to attenuate turbofan engine noise. To dampen the broadband noise and resist the harsh service conditions with high temperature and pressure in modern turbofan engine, new acoustic liner concepts are proposed and evaluated in the latest decade. In this review, available studies regarding the recent development of liners are gathered. The paper starts with the introduction of acoustic absorption mechanism of local-reacting and extended-reacting liners. The progress of novel passive liners (e.g., mesh-cap liner, variable-depth liner, metal foam liner, hybrid liner, etc.) is summarized. Furthermore, adaptive liners with tunable geometry dimension or bias flow are illustrated in details. Metamaterial is also mentioned as a hot candidate in the next generation of acoustic liners. Finally, this review identifies benefits and some technical challenges with the goal of unveiling the potential of novel acoustic liner technologies in aero engine.