Novel liner concepts

Abstract

Modern, low emission aero-engine concepts like for instance Ultra-High-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.

Aircraft noise generation and assessment: executive summary

“…The chapter on engine noise is comprised of three contributions, i.e., Refs. [6][7][8], that are briefly summarized here.…”

“…To address the demand of modern low-emission aeroengines for improved acoustic damping in a broadband frequency range, two different novel acoustic liner concepts are introduced in Ref. [8]. The first one, called Zero-Massflow Liner (ZML), enhances the acoustic damping of a liner by inducing an additional periodic in-and outflow through the liner perforation.…”

Broadband and Low-Frequency Acoustic Liner Investigations at NASA and ONERA

“…[4] Other concepts have targeted broadband sound absorption, such as checkerboard liners, [5] dual-resonance liners, [6] and liners that incorporate flexible walls within the liner core. [7] Many concepts have employed features to adaptively modify the impedance to enable in situ tuning of the sound absorption frequency range. For example, Bielak et al [8] used bias flow and temperature control to modify the sound field within the liner, whereas Bake and Knobloch [7] achieved similar results by embedding a loudspeaker within an SDOF liner (hybrid zero massflow liner).…”

“…[7] Many concepts have employed features to adaptively modify the impedance to enable in situ tuning of the sound absorption frequency range. For example, Bielak et al [8] used bias flow and temperature control to modify the sound field within the liner, whereas Bake and Knobloch [7] achieved similar results by embedding a loudspeaker within an SDOF liner (hybrid zero massflow liner). Shape memory alloys [9] and tunable electromechanical Helmholtz resonators [10] have been used as adaptive techniques for in situ impedance control, and Ichihashi [11] describes an acoustic structure for which the open area through the septum can be varied via flappers.…”

Analysis of a Film Forming Process through Coupled Image Correlation and Infrared Thermography

“…In current studies, novel cellular hybrid composite structures have been investigated for the application in sound-absorbing liners for aerospace applications [ 1 , 2 ]. Besides the Helmholtz resonator effect, the described structures utilize flexible wall areas with high intrinsic material damping to enhance acoustic performance [ 3 ].…”