An initial assessment of porous metal foam liners for acoustic broadband damping

Abstract

The noise spectrum of future aircraft engines is expected to be more broadband and less dominated by tonal content due to advances in fan blade technologies. Conventional liners excel at damping at their respective Helmholtz resonance with suboptimal broadband damping. This is where porous structures exhibit superior performance. They are commonly used in architectural acoustics and HVAC systems. However, in aircraft engine their applicability has been limited due to the harsh environment (temperature, fluids, bird strike, ...). A promising bridge is the use of highly porous metal foam liners who are able to withstand these conditions while offering significant broadband damping. This submission deals with the experimental characterization of metal foam probes and their acoustic properties in the context of a future application in an aero-engine. This includes the determination of the probe's flow resistance, impedance and dissipation of sound in the wind tunnel with grazing flow (DUCT-R) of the German Aerospace Center in Berlin.