On the conditions for the wind removal of soil particles

The airflow around spherical sand particles that have diameter of 200 μm and are deposited on the plane at regular distances close to or smaller than their diameter, equaled 50-250, 300 and 700 μm, is studied by considering the problem of wind removal of soil particles. The problem is solved using an open package OpenFOAM. A multilevel mesh is applied with adaptation to the shape of micro relief elements and smoothing the contact area of spherical particles with the lower plane with cylindrical shapes of small radius. The k-type of irregularities with large distances (above 300 microns) is used in calculations of the wind removal of particles. The proximity of the surface resistance values for the gaps between particles from 50 to 300-700 μm indicates the importance of taking into account the air motions in the pores inside a densely packed undersurface layer. The average distances between the particles were estimated by analyzing the sand porosity data. It is shown that they correspond to the case of d-type surface irregularities, when the processes in the layer between particles are significant. The distances of 100-250 μm are characterized by the presence of a recirculation zone in the region between the particles, which determines an order of magnitude greater surface resistance. The dynamic velocity is maximum for 200 μm and minimum for 100 μm; as the distance between particles changes, it also changes near the critical value at which a particle of this size can escape from the surface according to experimental data. Estimates of the height of the viscous surface layer for different distances between particles showed good agreement with the empirical data for relating this value to the roughness parameter. The buoyant force acting on the surface particles and calculated on the basis of estimates of the pressure difference on the opposite sides of the particles is maximum for the distances between the particle surfaces of 200 μm, minimum for 50 and 100 μm, and gives an inverse pressure against the surface for 150 and 250 μm