Evolution and Features of Dust Devil-Like Vortices in Turbulent
Rayleigh-Bénard Convection - An Experimental Study
Abstract
We present an experimental study simulating atmospheric dust devils in a
controlled laboratory experiment. Our work complements and extends the
numerical work of Giersch and Raasch (2021) by experiments. Dust devils
are thermal convective vortices with a vertical axis of rotation
visualized by entrained soil particles. They evolve in the convective
atmospheric boundary layer and are believed to substantially contribute
to the aerosol transport into the atmosphere. Thus, genesis, size,
lifetime and frequency of occurrence of dust devils are of particular
research interest. Extensive experimental studies have been conducted by
field measurements and laboratory experiments. Field measurements lack
of unpredictable formation of dust devils and limited area to be
observed. Hitherto laboratory experiments, which frequently generate
dust devils with fans, lack of generic conditions in the atmosphere. In
our study, we investigate dust devil-like vortices in a large-scale
Rayleigh-Bénard experiment. This set-up mimics the natural process of
dust devil formation as closest to reality so far. The flow measurement
was carried out by particle tracking velocimetry using neutrally buoyant
soap bubbles. We identified initial dust devil-like vortices by eyes
from the Langrangian velocity field and in a later more sophisticated
analysis by a specific algorithm from the Eulerian velocity field. We
analyzed their frequency of occurrence, observation time and size. With
our work, we could demonstrate that turbulent Rayleigh-Bénard convection
is an appropriate model to mimic the natural process of the genesis of
dust devil-like vortices in the thermal boundary layer of the atmosphere
without any artificial stimulation.