Mechanism and large eddy simulation of dust devils

Abstract

Large Eddy Simulations (LES) of vertical convective vortices and dust devils in the terrestrial Convective Boundary Layer (CBL) are presented. A CBL-scale simulation and a dust-devil-scale simulation are preformed at different resolutions. The CBL-scale simulation is performed to study the generation of vertical vortices and the dust-devil-scale simulation is performed to study the detailed structures and stages of dust devil development. The simulation results show that dust devils undergo three stages of development as the swirl ratio increases: a weak vortex stage, a single-celled vortex stage and a two-celled vortex stage. The structure of a dust devil can be divided into four regions: outflow, core, corner and inflow layer. The different structures and characteristics of the modelled dust devil during various stages of development and the influence of the surface on the dust devil profile are described using some of the simulation results as illustrations. The causes of the different structures and characteristics are analysed through the interplay between the rotation, the radial pressure gradient, the buoyancy and the axial pressure gradient. Dust devils are a type of concentrated vortex similar to tornadoes. The differences in the structure and characteristics of tornadoes and the modelled dust devils are discussed in this paper. The carrying aloft of sand particles within the modelled dust devil is explored using a Lagrangian coordinate system. Sand particles can be transported by the updraft with particles of varying diameters follow different tracks.

Large Eddy Simulation on Dust Suspension in a Convective Mixed Layer

“…The size of dust particles considered in the present LES range from 1 µm to 10 µm. This is smaller than those considered in Zhao et al (2004) and Gu et al (2006) and better corresponds to the ingredients of the Kosa.…”

“…There have been several LES studies on dust particles lifted by a dust devil (Zhao et al 2004;Gu et al 2006). In these studies, however, a single dust devil is produced in a cylindrical coordinate system and dust particles whose radius is on the order of several tens micro meters are distributed around the dust devils.…”

Dust Devil Sediment Transport: From Lab to Field to Global Impact

“…To date, most LES studies related to terrestrial dust devils have focused on vortex formation conditions and/or their physical characteristics (Kanak et al 2000;Kanak 2005;Zhao et al 2004;Gu et al 2008;Ito et al 2010b;Ohno and Takemi 2010;Raasch and Franke 2011;, with only a few such studies examining the fluxes of sand or dust. Zhao et al (2004) injected sand particles into their terrestrial LES to study particle trajectories in a dust devil.…”

“…Zhao et al (2004) injected sand particles into their terrestrial LES to study particle trajectories in a dust devil. The authors found that particles with diameters up to 160 µm could be transported in their simulated dust devils, with the largest particles being carried in the periphery of the vortices.…”

An Overview of Surface Conditions in Numerical Simulations of Dust Devils and the Consequent Near-surface Air Flow Fields

“…Many investigators have studied the principle of dust devil formation and most of them think that dust devils occur within rising plumes in the CBL (Battan, 1958;Ryan and Carroll, 1970;Cortese and Balachandar, 1993;Shapiro and Kogan, 1994), or within swirling rising plumes (SRP) (Zhao et al, 2004). The air near the ground of the SRP region is characterized by a superadiabatic lapse rate (Sinclair, 1976;Oke et al, 2007).…”