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Experimental Investigation of Shear Grazing Flow Effects on Extended Tube Acoustic Liners

  • Roncen, Remi
  • Sebbane, Delphine
  • Mery, Fabien
  • Piot, Estelle
  • Simon, Frank
Publication Date
Dec 07, 2020
DOI: 10.48465/fa.2020.0225
OAI: oai:HAL:hal-03221398v1
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ĂAircraft engines are one of the dominant noise sources for subsonic aircraft, resulting in a dense research field aimed at noise reduction inside the engine nacelle. In current turbofan engines, the inlet, bypass and exhaust parts of the nacelle are lined with acoustic liners. Liners consist essentially of a perforated plate backed by an air cavity, and have a resonator behavior. To meet the demand of future industry standards in terms of engine efficiency, Ultra High Bypass Ratio engines are now considered. The acoustic emission of these engines is at lower frequencies than the current ones, which require the design of acoustic liners than can target this frequency regime, at an ever reduced thickness. To do so, one possible solution is to implement tubes that extend within the cavity in order to reduce the resonance frequency. Perforated plates are known to have a non-linear behavior regarding the presence of a shear grazing flow. However, such studies have not been performed yet for materials possessing extending tubes in the cavity. The focus of the present work is put on an experimental investigation on the influence of a shear grazing flow on the impedance acoustic of liners whose upper sheet perforations are extended with tubes (Leonar concept). An impedance eduction process is performed on 8 different liners, at Mach numbers ranging from 0 (reference no flow case) to 0.3 and at frequencies close to the resonance frequency.

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