Investigating the Formation of Dust Devils through Linear Stability Analysis and Direct Numerical Simulations

Dust devils are organized vortical flows that arise from the interaction of buoyancy and circulation. While experimental investigations and numerical simulations have provided significant insights into their flow structure and dynamics, the exact conditions that trigger the formation of dust devils remain unclear. Although strong surface heating and circulation are known to be essential, the precise threshold values for these parameters are not well defined.

This study employs linear stability analysis and direct numerical simulations (DNS) to examine the linear and non-linear characteristics of an idealized dust devil model. In this model, the inlet swirl is controlled via the inlet flow angle while the the total inlet kinetic energy remains fixed. Linear stability analysis identifies a range of inlet swirl angles where the flow becomes unstable to azimuthal perturbations—a prerequisite for the formation of a dust devil. Additionally, the analysis reveals three distinct regions in the parameter space of inlet swirl angle versus buoyancy where the flow is unstable to azimuthal perturbations. The presentation will discuss the flow structure in these regions and demonstrate that only one of these unstable regions provides the essential conditions for the formation of dust devils.