Modelling, manufacturing and testing of acoustic plate resonator liners

Abstract This paper presents the results of a study in which the concept of the plate resonator as an acoustic engine liner was thoroughly investigated from an acoustic and a manufacturing perspective. Since future jet engines will present new challenges such as low-frequency tonal noise, e.g. due to larger fans, new lining concepts need to be developed to solve these future noise problems. The plate resonator concept represents a possible alternative to conventional linings. Therefore, a semi-analytical model is used to carry out extensive parameter studies to better understand the fundamental operating mechanisms of plate resonators. A suitable plate material for the resonator is also derived from the parameter studies. Based on this, a plate resonator liner prototype is designed and additional investigations are carried out to determine the properties of the considered material. Afterwards, the design is manufactured in lightweight construction taking into account the engine-specific requirements. To verify this concept, measurements are carried out in an aeroacoustic test rig investigating two plate resonator liners. Thereby, the effects of pre-tension applied to the plates and grazing flow are analysed. The aim of realising low-frequency attenuation under the condition of limited installation space is successfully achieved by the plate resonator concept. In addition, the capability of using the semi-analytical model for specific design purposes is proven. The feasibility of implementing this concept in a jet engine nacelle is also investigated by considering a lightweight manufacturing process. The results of this work provide a solid base for new lining concepts and contribute to the goal of making future air traffic much quieter.