Acoustic absorption of 3D printed samples at normal incidence1and as a duct liner
In recent years, it has become possible to produce acoustic absorbers with geometries that were previously difficult to manufacture, thanks to advances in 3D printing techniques. This requires, on the one hand, the ability to print precisely the designed geometries and, on the other hand, the ability to predict the acoustic behaviour of the printed materials in the desired configuration. The objectives of this thesis are to study the effect of dimensional variability of samples produced by 3D printing on acoustic performance and to examine different methods for predicting acoustic performance, ranging from comprehensive but expensive microscopic approaches to rapid but simplified macroscopic approaches. Stereolithography was chosen to print the samples following a review of the printing methods evaluated in the literature. Different variations of principal geometry are studied. The relevance of an equivalent fluid approach is demonstrated : it can faithfully reproduce, at reduced cost, the results of a direct approach, solving the linearised Navier-Stokes equations in the pores of samples.
The samples are first studied at normal incidence. The measurement results and the predictions are in good agreement overall. This confirms the validity of the equivalent fluid model at normal incidence, which is classically treated in the literature. Samples were then made specifically for testing in the duct wall, and their acoustic performance was investigated by measuring the transmission loss. Again, the experimental results confirm the relevance of using the equivalent fluid approach to predict the acoustic behaviour of this type of material under a grazing incidence.
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