Experimental and Numerical Investigation of the Turbulent Boundary Layer of a Grazing Flow Over Porous Materials

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.