Abstract: The interaction between non-erodible particles and turbulent structures in aeolian plays a crucial role in understanding sediment dynamics. In recent decades, the degradation of air quality due to the suspension of fine particulate matter has become a global concern. Aeolian erosion is a significant source of airborne particles, including dust and pollutants, which can cause damaging impacts on human health and on the environment. The role of non-erodible roughness elements in shaping turbulent flow and influencing particle entrainment is central to understanding and develop more accurate emission models that underlies mitigating actions. This study investigates the effects of non-erodible particles on turbulent structures development foccusing on the influence of particle shape representations: cylinders and semi-spheres. Large-Eddy Simulations (LES) of the wind flow over particle beds using both particles shapes were perfomed. The governing equations used are those based on the filtered Navier-Stokes equations for mass and momentum. The physical model consists of an infinite bed formed by a mixture of erodible and non-erodible particles in a neutral atmosphere. Non-erodible particles are represented by random fixed cylindrical or semi-spheres roughness elements and the erodible particles by the smooth surface around them. Just one portion of the bed is considered in the numerical simulations. Ansys Meshing® 19.0 software was used to construct a hexahedral mesh of 4,188,797 elements. The mesh was built by extrusion of hexahedral cells defined on the ground and cylinders walls with a growth rate of 1.1. To reach LES model requirements, the minimum element size on the walls was setup same order as 10−4 m and the time step 2.5× 10−5 s. The minimum size was obtained considering that for LES, y + < 1. For upstream and downstream (x-direction) boundaries the periodicity condition with mass flow rate of 0.0051 was assumed. On the lateral sides (z-direction), the periodicity condition was also assumed, but the fluid flows in order that the mass balance within the domain is guaranteed. For top and bottom boundaries and rough surface it was assumed non-slip conditions. To obtain initial conditions for LES, Reynolds Averaged Navier-Stokes (RANS) simulations was performed using the k − ω Shear-Stress Transport (SST) model. As one of the objectives of the present work is to evaluate the evolution of the flow from a smooth surface to the appearance of rough elements, it is also necessary to evaluate a smooth surface. To avoid additional computational costs, it was considered that the top of the domain could keep all the characteristics of a smooth bed as long as the distance of up to y + = 30 from the wall is respected. Typical turbulence statistics results obtained with LES were compared with experimental and Direct Numerical Simulation (DNS) data of Durst et al. (1987) and Kim et al. (1987), respectively. The comparison between the results obtained shows that the values measured by Durst et al. (1987) have good agreement with the values simulated using LES. The turbulent structures over the particle roughness, ejection regions associated to multiple-sized grains over time, and the probability density functions of the friction velocity in both cilinder and semi-sphere shapes are examined. The evaluation of particle shape impact on trubulent structures and sediment transport provides valuable insights into the relationship between non-erodible particles and the processes of aeolian erosion. The findings contribuite to a deeper undertanding of the mechanisms governing this phenomenon and have implications for environmental science and engineering.

Keywords: Aeolian erosion, particle emission, turbulent structures, particles shape, Large-Eddy Simulations.