Optimising the absorption and transmission properties of aircraft microperforated panels

Abstract

A method for evaluating the absorption and transmission performances of multi-layer micro-perforated structures whose facings are excited by different noise sources is described here. It is applied to determine if the acoustical performances of a number of Micro-Perforated Panels (MPPs), optimised both in absorption and transmission, exceed those of typical aircraft panels undergoing internal and external acoustic excitations. A fully-coupled modal formulation is presented that accounts for the effects of the sub-structure volumetric resonances on the acoustical properties of the partitions. It is validated against full-scale measurements performed with a pressure–velocity probe and a laser vibrometer to estimate the absorption and transmission coefficients of single- and double-layer micro-perforated partitions. The model is used to optimise the sound power dissipated by three layouts obtained from a typical aircraft partition by micro-perforating the trim panel (MPP–Porous–Panel), removing the fibreglass material (MPP–Cavity–Panel) and adding a second MPP inside the separating cavity (MPP–MPP–Panel). It is concluded that the MPP–Porous–Panel and MPP–MPP–Panel layouts provide excess interior noise reduction above 1.8kHz and 1.2kHz respectively, whereas the MPP–Cavity–Panel is not acoustically more efficient than a typical aircraft panel.