Flexible membrane type non-linear liner

Palani, Suresh, Subramanyam, Ramesh Raja, Paruchuri, Chaitanya and Joseph, Phillip (2023) Flexible membrane type non-linear liner. 29th International Congress on Sound and Vibration, , Prague, Czech Republic. 09 Jul - 13 Aug 2023.

Abstract

Acoustic liners are widely used passive noise reduction technology for aero-engine noise control. Traditional acoustic liners installed in an aero-engine are usually modelled as a Helmholtz resonator, an air-filled cavity sandwiched between a perforated plate and an acoustically rigid back sheet. For wavelengths much greater than the liner's geometrical dimensions, the air-filled cavity is regarded as a spring, and the volume of air inside the perforations of the face sheet as a mass, acting as a Single-Degree-Of-Freedom (SDOF). Such an SDOF liner design typically provides a narrow absorption bandwidth at a resonance frequency lower than a simple quarter-wave resonator. In this preliminary work, the acoustic properties of a novel liner concept called flexible slanted septum core have been studied experimentally. An overall increase in the absorption coefficient and a significant shift in the frequency range towards lower frequencies have been observed at moderate sound pressure levels (SPL). The shift in absorption frequency bandwidth is mainly attributed to the elastic constant and intrinsic damping of the flexible membrane-based perforated face sheet and slanted septum. Additionally , when excited with a high SPL sound source, the flexible liner concept showed much improved sound absorption with broadened frequency bandwidth, acting as a "non-linear" flexible membrane type liner.

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Contributors

Author: Suresh Palani

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