Towards Development of an Active Single-Layer Acoustic Liner for Jet Engine Noise Reduction

Experiments and a Lumped Element Model are used to develop an acoustic liner with an increased degree of freedom by adding a compliant face sheet to the system. The model is setup to include the neck and cavity geometry of the liner and a compliant face sheet. The model is then used to predict the impedance of the liner due to the Helmholtz resonator and the compliant face sheet. A set of experiments were run in a wave tube apparatus to measure the impedance of various acoustic liners. The parameters studied included varying the diameter of the hole in the face sheet, the cavity depth, and face sheet thickness. The model and experimental results were compared, and it is shown that the model is good at predicting the absorption properties for the various geometries. Depending on the coupling between the liner geometry and the compliant face sheet, the absorption characteristics were altered. The bandwidth of noise suppression (absorption coefficient > 0.8) was 500 Hz for a 0.2” diameter hole, a 1” cavity depth, and a material thickness of 0.012”.

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