Numerical analysis of transport in porous media to reduce aerodynamic noise past a circular cylinder by application of porous foam

Abstract

Metal foams as porous media have very high porosity and good strength. These materials could easily be applied to exterior surfaces of metals used in different industries. Porous media have been used less in the external flows to control the wake region or reduce the generated sound in high-speed flows. In this study, a numerical investigation is done to explore the effect of different characteristics of a porous medium—such as PPI and porosity or porous coating thickness—on the sound generated by a porous-coated cylinder. The governing transport equations in the clear and porous regions are solved using 3D Navier–Stokes and non-Darcy equations, respectively, and employing the large eddy simulation turbulence model. The generated noise is estimated using the Ffowcs-Williams and Hawkings model at the observer location. The results show that use of porous media could considerably reduce the aerodynamic noise provided that its characteristics are selected precisely. For example, results show that a porous-coated cylinder with PPI = 40 has about 30 dB higher overall sound pressure level (OASPL) than one with PPI = 10 with the same porosity and thickness. Same conditions are also observed about the thickness of the coating. The results indicate that an optimal thickness exists for which the OASPL is minimal. For example, porous-coated cylinders with coating thickness of 5 and 15 mm have about 25 dB higher OASPL compared to a cylinder with the coating thickness of 10 mm.