Investigating The Dissimilarity Between Dust And Momentum Turbulent Transports Using Large Eddy Simulation

The ability to estimate the dust exchange between the surface and the atmosphere has tremendous importance owing to mineral dust’s impact on micro-climate, agriculture, human health and economic activities. This exchange involves the release of dust grains into the turbulent boundary layer through sandblasting, their dispersion by the turbulence, and their deposition back onto the surface. In order to simulate this exchange, one needs to simulate both the flow turbulence and the saltation process - which supplies energy for dust emission. To this effect, a Large Eddy Simulation (LES) airflow model capable of explicitly simulating the main turbulent eddies of the flow was used. This model was coupled with a Lagrangian model for saltation that resolves individual saltator trajectories and accounts for the two-way interaction between the saltator motions and turbulent flow. A splash scheme was employed to account for particle rebound and ejection at the surface, and to derive energy required for dust emission. A simple energy based dust emission scheme that links surface cohesive forces to dust particle size was developed. Finally, an Eulerian dust dispersal model was incorporated to simulate the transport of the dust plume. The model is evaluated against the WIND-O-V’s 2017 field experiment performed in Tunisia in 2017, where wind dynamics, saltation flux and dust flux were measured. An interesting outcome of this campaign was the dissimilarity in the transport of dust and momentum, contrary to existing views. The high intermittency of dust emission compared to the more continuous momentum absorption at the surface may explain this dissimilarity. The LES model is used here to explore the sources of dissimilarity between the dust and momentum turbulent transports.