Novel liner concepts

Modern, low-emission aero-engine concepts, such as, for instance, Ultrahigh-Bypass Ratio (UHBR) designs, claim higher demands on the damping performance of acoustic wall treatment, called liner, installed in the engine. New liner concepts are needed providing a more broadband damping efficiency ranging explicitly to the low-frequency range. However, space and weight constrains are still also one of the crucial criteria which need to be fulfilled by the liner structure. To overcome this challenge, two novel liner concepts are presented here. One concept, the hybrid ZML, combines the classical Single-Degree-of-Freedom (SDOF) liner with a Zero-Massflow-Liner (ZML) principle. The other one, the FlexiS concept, takes advantage of the intrinsic material damping of flexible walls within the liner structure. A proof of concepts study of both novel concepts is provided highlighting the enhanced damping performance with respect to broadband capacity and low-frequency damping