Micro-Perforated materials for the reduction of flow-induced noise

Turbulent Boundary Layer (TBL) induced noise is one of the dominant noise sources in modern aircraft. The aim of this work is to study the behavior of insulating partitions composed of Micro-Perforated Panels (MPPs) exposed to a TBL excitation. We have carried out a set of simulations to establish a comparison between the performance of the MPP control devices when varying the physical configurations of the partition and the nature of the primary noise excitation. It can be shown that when exciting the partition with less correlated random loads, the corresponding TL increases progressively. Experiments have been performed in the low-speed wind tunnel in order to determine the acoustic and aerodynamic TL performance of a number of MPP multilayer partitions. The effect of inserting a micro-perforated panel within the cavity at unequal distances from the front and back panels dampens more efficiently the Mass-Air-Mass controlled resonances of the Panel-Cavity-Panel system with respect to those of the MPP-Cavity-Panel system, already damped by the front MPP. This results in a higher TL difference between the triple and double partitions with a plain front panel, which is about 8 dB, with respect to the same configurations with a microperforated front panel, about 4 dB.