Validation of a model for acoustic absorption in porous media

The analysis of porous materials for aeroacoustic noise mitigation requires high-fidelity numerical tools to simulate the sound propagation and interaction in porous media. The manuscript presents the calibration and validation of a direct-hybrid LES/CAA method used to model the aerodynamically generated sound. The porous micro-structures are modeled with a volume-averaging approach. Additional terms, emerging in the governing equations, owing to the force exerted by the porous matrix on the fluid, are closed by means of Darcy's law and the quadratic Forchheimer term. The sound generation and propagation is predicted by a solution of the acoustic perturbation equations via a discontinuous Galerkin method. The model for the porous material is separately calibrated for the CFD and CAA with the parameters retrieved by the characterization of a melamine foam in experimental tests. The sound predicted by an absorbing layer of the material is compared with measurements performed in an impedance tube. Secondly, the transmission coefficient of the melamine foam placed in an acoustic liner configuration inside a duct is studied numerically. The results are then compared with experiments conducted in absence of a flow and also with a flow velocity of 30 m/s in order to assess the accuracy of the model calibration.