LEONAR liner concept: multiphysics coupling in presence of grazing flow, thermal gradients and high sound levels
Résumé
The development of turbofans with larger fan diameters, shorter inlets, and thinner walls forces the acoustic liners to be placed closer to the hot parts of engines. This experimental study investigates the combined effects of important thermal gradients, grazing flow and acoustic level on the acoustic behavior of liners applied to the LEONAR (Long Elastic Open Neck Acoustic Resonator) liner concept. Previous studies have shown that a coupling between these three effects can exist. The objective is thus to understand the underlying coupled phenomena, in order to emphasize the interest of such a liner concept regarding a classical equivalent SDOF liner. In the ONERA B2A grazing flow acoustic liner facility, the flow temperature can be accurately regulated and several types of acoustic excitation can be provided. A test section with a heating or cooling device is used to obtain a thermal gradient between the backplate and the perforated plate of the liner sample, and infrared (IR) thermography is used to measure the temperature distribution on the perforated plate. The measurement is conducted on several configurations and with different types of liners, to assess the behaviors of the LEONAR liner concept in the context of the UHBR.
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