The aeroacoustic performance of porous materials for sound-control applications depends on the flow communication through the medium. Hence, flow-permeable noise-reduction technologies should be tailored to the flow they operate within. A large-scale simulation setup has been developed in this work to aid the design of porous materials for airframe-noise mitigation by modeling their aerodynamic and acoustic behavior. However, this aerodynamic modeling setup requires validation on a more fundamental flow case. To this purpose, large-eddy simulations of the turbulent boundary-layer flow over two porous materials and a reference solid wall are compared against wind-tunnel measurements. This analysis includes velocity-derived boundary-layer profiles and unsteady wall-pressure measurements on the upper and lower surfaces of the flow-permeable medium. The generated experimental data are additionally made publicly available as a benchmark for boundary-layer flows over a porous wall-insert. The results of the simulation show a satisfactory agreement with the experimental data in most cases, especially for the solid wall. The mean-velocity and turbulence-intensity profiles and the wall-pressure spectra of the boundary layer over the porous materials show a dependence on the streamwise position along the surface, leading to a decrease in wall-pressure energy below a Strouhal number based on the boundary-layer thickness and the outer-flow velocity of 3 and an increase above it. Future research will be aimed at developing a new model for porous media flow centered on the optimization of the flow communication paths within them. This will potentially allow the development of porous materials with favorable acoustic properties while minimizing their aerodynamic penalty.@en

The noise emission of a simplified two-wheel nose landing gear configuration featuring a detachable porous fairing is investigated by a hybrid CFD/CAA approach. The noise mitigation properties of the porous fairing are discussed and compared against two reference configurations, i.e., baseline configurations with and without a solid fairing. The time resolved flow and acoustic near field is computed by a lattice Boltzmann (LB) method with a collision step based on countable cumulants, and the noise radiation into the far field is predicted by solving a permeable surface Ffowcs Williams and Hawkings formulation. The porous material is represented by an equivalent forcing term in the LB equation based on a Forchheimer-extended Darcy model. The porous material has a deterministic geometric structure such that the modeling parameters describing the porous material properties are determined by results from a flow simulation through the resolved micro-structures in a periodic pressure drop setup. The effect of the different fairings on the flow field and the resulting acoustic far field pressure are discussed.@en

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.

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