Aerodynamic noise simulation of porous medium-coated cylinder: Broadband hump noise mechanism and effects of permeability and pores distribution on tonal noise

The porous medium layer can effectively control the aerodynamic noise generated by the flow around a cylinder. To analyze the internal flow within porous media and the impact on aerodynamic noise, a quasi-microscopic porous medium model composed of a square cylinder array is adopted. Based on the lattice Boltzmann method (LBM), simulations under different porosities and pores per inch (PPI) at $Re=8.2\times {10}^4$ have been performed. The results indicate that the porous medium induces additional mid-to-high-frequency broadband hump noise, which is generated from vortex shedding of the porous medium skeleton units (PSUs). This study investigates the impact of varying permeability on the frequency and maximum sound pressure level (SPL) of tonal noise while keeping effective mean diameter and porosity constant respectively. With a fixed effective mean diameter, an increase in permeability leads the frequency and maximum SPL of tonal noise firstly decreasing and then stabilization. Under a fixed porosity, no discernible correlation is observed between variations in the permeability and the maximum SPL and frequency of tonal noise. The research on PPI reveals that the circumferential PPI does not exert a significant influence on tonal noise maximum SPL, and reducing radial PPI yields a substantial decrease in tonal noise maximum SPL.