Liner Multiphysics Coupling Between Grazing Flow, Thermal Gradients, and Sound Pressure Levels

Abstract

The evolution of turbofan engines has led to designs with larger fan diameters, shorter inlets, and thinner nacelle walls. This has forced the acoustic liners used therein to be placed closer to engine components that undergo significant thermal heating. This experimental study investigates the combined effects of important thermal gradients, grazing flow, and acoustic level on liners applied to the Long Elastic Open Neck Acoustic Resonator (LEONAR) liner concept. Previous studies have shown that a coupling between these three effects can exist. The objective is to compare such a liner concept to a classical equivalent single-degree-of-freedom liner and to highlight differences in this coupling behavior. Experiments are conducted in the grazing flow duct at ONERA (B2A), where 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 thermography is used to measure the temperature distribution on the perforated plate. The measurement is conducted on several configurations to assess the behaviors of the LEONAR liner concept in the context of combined influence of grazing flow, thermal gradients, and high sound levels.