Verification of liner panel designs based on impedance educed by direct methods

Acoustic and aerodynamic properties of perforated liner panels under grazing flow conditions are of great importance in designing the lined nacelle for higher-bypass-ratio and short-inlet aircraft engines. One of the key properties is the acoustic impedance. In this study, acoustic impedances of liner panels are evaluated by applying a direct method, based on the scattering matrix, to acoustic and aerodynamic data obtained by the flow-duct-type rig in JAXA. Several types of liner panels were designed, manufactured, and tested under grazing-flows with different mean velocities up to Mach 0.35. The tested panels include a baseline liner with the same geometry to the referenced one. The impedance of the baseline liner obtained in this study was in good agreement with the reported value. This proves the validity of our measurement and eduction methods. We plan to apply the educed impedances to a duct in a small turbofan engine, DGEN380, to predict the noise reduction. The predicted noise reduction will be compared with the measured one, and will be provided in the final paper.