A HIERARCHICAL APPROACH TO DETERMINING ACOUSTIC ABSORPTION PROPERTIES OF POROUS MEDIA COMBINING PORE-RESOLVED AND MACROSCOPIC MODELS

Abstract

Acoustic properties of porous media are very important for numerous industrial applications, the typical goal being to maximize broadband absorption to decrease the sound pressure level of the engineering system under consideration. Up to now acoustic absorption for porous media with complex inner geometry is determined experimentally, as acoustic simulations on the pore scale are computationally challenging due to the tedious geometric reconstruction of computer tomography (CT) data and the corresponding mesh generation as well as substantial computational requirements for the corresponding transient 3D solvers. The lattice Boltzmann method (LBM), which is an established computational approach to simulate pore-resolved porous media transport problems, has been used successfully for aeroacoustic setups and is utilized in this work to fill this gap. This paper presents a comparison of different experimental and numerical approaches to determine the acoustic absorption of different porous media. Experimental work with an impedance tube was carried out for comparison and CT scans were conducted to supply the detailed numerical simulation with geometry data of the porous samples. Results of LB simulations for the acoustic impedance of a microperforated plate and a felt are shown. Finally we demonstrate how microscopic parameters determined by a pore scale approach can be used to feed homogenized models to bridge the gap towards simulations of components where acoustic absorbers are applied to, e.g., wing flaps of airplanes.