Study on noise reduction performance of two-dimensional pillar shapes and porous medium

Abstract

To study the effects of two-dimensional (2D) pillar shapes and the parameters of porous materials on flow field characteristics and aerodynamic noise, this study employs the Improved Delayed Detached Eddy Simulation (IDDES) method combined with the Ffowcs Williams-Hawkins (FW-H) equation to numerically simulate the flow field and aerodynamic noise of the pillars with variable cross-sections (cylindrical pillar, elliptical pillar, rounded square pillar and square pillar) and pillars covering with porous medium. The parameters of the porous medium under investigation include: porosity ($\varphi$), particle diameter (dp) and medium layer thickness (h). Proper Orthogonal Decomposition (POD) was utilized to perform reduced-order analysis of unsteady flow in the wake region, revealing the physical significance of POD modes of different pillars in wake evolution. The results indicate that the elliptical pillar exhibits the best performance in noise reduction, with its design allowing for a maximum reduction of 7 dBA in the far-field overall sound pressure level, among the four types of pillars with variable cross-sections. And the three types of porous medium parameters significantly affect the noise reduction performance of the pillar. Among them, the pillar with parameter combination of dp = 500 μm, $\varphi$=0.97, and h = 0.25 D exhibit superior noise reduction effects, with a maximum reduction of 10.2 dBA in the far-field overall sound pressure level. Porous medium layer with reasonable parameters can significantly delay boundary layer separation, extend the stable region of the shear layer, and attenuate velocity and vorticity magnitudes in the wake region, thus suppressing turbulence fluctuations and aerodynamic noise.