Experimental and calculation investigation on perforated Liners’ acoustic impedance

Abstract Acoustic impedance models are the most common method for representing the properties of engine nacelle liners. Although various models have been developed, it is difficult to validate the accuracy due to the limitation of impedance eduction techniques. For obtaining accurate impedance results, a series of perforated liners are manufactured and the impedance of all is measured by using both the microphone array method and in-situ method. The results of the test demonstrate that acoustic resistances are not sensitive to percent open areas, hole diameter, and the face sheet’s thickness, but the Mach number of the grazing flow in the duct can have a considerable effect on resistance. Furthermore, excellent agreement between predictions and measured data gives confidence that the Goodrich perforated liner impedance model is suitable for the design of engine nacelle liner.