Roughness effects on turbulent flows over Gaussian geometries using Large Eddy Simulations

This study explores the effects of wall roughness density on turbulence characteristics through Large Eddy Simulations (LES). The roughness is modeled using Gaussian functions, and the focus is on how variations in roughness density influence higher-order statistical properties, such as Reynolds stresses and turbulence anisotropy. The findings show that rough walls cause a downward shift in the mean velocity profile, denoted as ΔU+, with turbulence becoming more isotropic as the roughness height increases. The study specifically examines the influence of roughness density by comparing configurations obtained through 32- and 64-Gaussian functions. The results indicate that increasing the roughness density from 32 to 64 elements leads to a smaller impact on the turbulent flow field. This outcome is consistent with previous work, where it was shown that, for the same mean height of roughness k/h, the reduction in the velocity profile becomes less pronounced as the roughness density increases. In other words, while an increase of the roughness height results in a larger shift in the velocity profile, the effect diminishes with increasing roughness density, as seen with the 64-Gaussian configuration compared to the 32-Gaussian one. In addition, the study investigates the influence of roughness on turbulent structures such as streaks and vortical formations. The results confirm that roughness modifies the spatial organization of turbulence, with increased roughness height leading to wider vortical structures and more intermittent streaks. These observations contribute to a better understanding of how surface roughness affects turbulence dynamics, highlighting the complex relationship between roughness density, flow behavior, and turbulence organization near rough walls.