Acoustic behaviour of micro-perforated panel backed by shallow cavity under fully developed grazing flow

Abstract

This paper presents numerical and experimental investigations into the acoustic behaviour of a micro-perforated panel (MPP) backed by a shallow cavity under a fully developed grazing flow. A three-dimensional time-domain computational fluid dynamics approach is applied alongside hybrid evaluation methods to accurately capture the acoustic behaviour variations of an MPP orifice, considering the interaction of flow dynamics and the acoustics in the orifice and cavity. Meanwhile, a hybrid Rayleigh's end correction model for T-shaped resonators is utilized to calculate the acoustic reactance of a very shallow cavity. The numerical results show that the vertical shear layer is observed alongside the hole and cavity and impinges the bottom of shallow cavity. Subsequently it alters acoustic and flow interaction significantly that leads to variation of acoustic behaviour of orifice. In this regard, an acoustic impedance model of an orifice backing with shallow cavity at grazing flow is established. The proposed acoustic impedance model of orifice has been validated by experimental study. The transmission loss predictions for a compact MPP absorber with single or double cavities agree well with the experimental results for the grazing flow condition. The practical significance of this study is that it elucidates the influence of cavities upon the acoustic behaviour of MPPs in the presence of grazing flow; furthermore, it proposes an impedance model that is more suitable for predicting the acoustic performance of booming compact meta-structures.