Acoustic absorption of 3D printed samples at normal incidence and as a duct liner

Prediction of the acoustic performance of 3D printed materials is investigated at normal and grazing incidence. A direct numerical (microscopic) simulation that solves the full set of Navier–Stokes equations is used as a reference. It is compared with a macroscopic approach in which the material is represented by an equivalent fluid. The materials have a periodic microstructure, consisting either of a single network of spherical or cubic cavities connected by cylindrical channels or of a double-nested network. The samples are printed using the stereolithography technique and are tested using an impedance tube and a duct test bench. For single network geometries, the results of sound absorption at normal and grazing incidence predicted using the equivalent fluid approach are in good agreement with those obtained by the microscopic approach. Comparisons with impedance tube measurements confirm that both approaches can accurately predict the absorption coefficient of the samples. For the in-duct liner configuration, the transmission loss measurements and predictions show similar evolution with frequency change, despite the discrepancy in amplitude. For the double network geometry, the equivalent fluid approach cannot exactly reproduce the results obtained with the direct numerical simulation. Finally, while the predictions with the microscopic approach provide a good match with the impedance tube measurements, only a poor agreement is obtained using the duct testing bench.