CONCENTRATION AND TURBULENT DIFFUSIVITY OF SAND PARTICLES IN THE ATMOSPHERE BASED ON MIXTURE MODEL THEORY

Abstract

The particle concentration is analyzed numerically with a mixture model in multiphase flows. Multiple applications of this model in liquid-particle flows ensure its reliability. In the Aeolian sand transport, the density of the dispersed phase is small (on the order of 10^-5-10^-4. The mixture momentum equation and the continuity equation can be approximated using the single phase for an incompressible gas where the dispersed phase slip velocity (<i>u</i>_slip) is relative to the continuous phase. The slip velocity was calculated based on the balancing between the body and drag forces due to the density difference. The simulation results based on the mixture theory were determined in comparison to previous test results. The velocity profiles and particle concentration are presented. The results confirm that particle concentration decreases exponentially with altitude. The variation of the diffusion coefficient of sand particles (<i>D</i>_md) with height direction can be traced as a Gaussian distribution, which is influenced by the transported particle size and its kinetic energy. The smaller particle sizes have a larger diffusion coefficient than those with the larger ones. According to the ratio of Schmidt number, it describes the relationship between the rates of turbulent momentum transport and turbulent mass transport, which can explain the effect of wind kinetic energy on the sand turbulent diffusion profiles. The mixture approach application is in good agreement with previous wind tunnel works. This approach can be applied to study the turbulence properties in the Aeolian sand transport.