Absorption and Transmission of Boundary Layer Noise through Thin Micro-Perforated Panel Structures

Micro-perforated panel (MPP) partitions have shown great potential in building acoustics to enhance the sound absorption and improve the sound transmission loss (TL) induced by plane wave or acoustic diffuse field excitations. However, the acoustical performance of these lightweight structures has been scarcely studied when excited by a turbulent boundary layer (TBL), albeit of relevance in surface and air transport systems due to the emergence of aerodynamic noise sources. In this work, the absorption and transmission properties of MPP-Cavity-Panel (MPPCP) systems under an aero-acoustic excitation are investigated through analytical and experimental studies. A methodology is proposed to estimate the power flow injected by wall-pressures into MPPCP partitions flush-mounted in a low-speed wind tunnel as well as their transmission coefficient. The measurements show significant differences in the absorption and TL variations when considering either a low-speed TBL or a pure acoustic excitation. They are confirmed by predictions on finite- and infinite-sized partitions whose excitation comprises both acoustic and turbulent components. A parametric study is carried out on the sensitivity of the absorption and TL to the mean flow velocity, the MPP holes diameter and perforation ratio as well as the weighting between the acoustic and turbulent components of the excitation.