Numerical Simulation of Dust Lifting within Dust Devils—Simulation of an Intense Vortex

Abstract

Based on an advanced dust devil–scale large-eddy simulation (LES) model, the atmosphere flow of a modeled dust devil in a quasi–steady state was first simulated to illustrate the characteristics of the gas phase field in the mature stage, including the prediction of the lower pressure and higher temperature in the vortex core. The dust-lifting physics is examined in two aspects. Through the experimental data analysis, it is verified again that the horizontal swirling wind can only make solid particles saltate along the ground surface. Based on a Lagrangian reference frame, the tracks of dust grains with different density (material) and diameter are calculated to show the effect of dust particles entrained by the vertical swirling wind field. The movement of solid particles depends on the interactions between the aloft dust particles and the airflow field of dust devils, in which the drag and the centrifugal force component on the horizontal plane are the key force components. There is the trend of the fine dust grains rising along the inner helical tracks while the large dust grains are lifting along the outer helical tracks and then descending beyond the corner region, resulting in the impact between different-sized dust grains in the swirling atmospheric flow. This trend will make the dust stratification, developing a top small-sized grain domain and a bottom large-sized grain domain in dust devils.

Particle Image Velocimetry of a Dust Devil Observed in a Desert

“…The dust devil investigated in this paper was not remarkably strong among those observed in the same day. This suggests that dust devils in the real atmosphere have much faster tangential and vertical velocities than those reproduced in numerical simulations (e.g Kanak 2005; Gheynani and Taylor 2010; Raasch and Franke 2011;Ito et al 2013) except for an experiment in which ambient rotation is forced at the lateral boundary (Gu et al 2006). …”

“…For the lower heights, a region with large D may be associated with stronger tangential wind that picks up a large amount of dust particles from the ground. On the other hand, large D near the top is likely to be caused by dust particles thrown out from the central core by the centrifugal force (Gu et al 2006), resulting in the slower rotational speeds.Vertical winds w are estimated from v → that satisfies −24 < u < −12 m s −1 in order to focus on the flows near the core. The resulting weighted frequency has a positive bias (Fig.…”

“…Vertical velocity may not be uniform in the dust devil (e.g. Gu et al 2006) so that it is natural that the peak of w becomes very broad. Height of the dust column also increases at a rate of approximately 5.9 m s −1 (Fig.…”

Dust opacities inside the dust devil column in the Taklimakan Desert

“…The method to quantify spatial distribution of opacity is able to present the similar spatial variability like grid boxes defined in DD numerical models to simulate spatial distribution of physical properties (Mason et al, 2013;Gu et al, 2006). In the further study, we could use the regular grids for a better comparison between differently shaped dust devils, in particular for dust devils that are not well-structured and might deviate substantially from an ideal conical shape.…”

“…The method to quantify spatial distribution of opacity is able to present the similar spatial variability like grid boxes defined in DD numerical models to simulate spatial distribution of physical properties (Mason et al, 2013;Gu et al, 2006). In addition, other cases with the undermined height and width of DDs also show similar structures (Fig.…”