Experimental investigation of Dust Devil like vortices with 3D particle tracking velocimetry

Dust devils are atmospheric air vortices with a vertical axis, which are formed by strong sun radiation and the resulting vertical temperature gradient. The structure of a typical dust devil is dominated by a radial inflow near the surface and a vertical upward flow within the vortex. Since experimental investigations are limited to local in-situ measurements of the atmosphere, many mechanisms related to their formation and their characteristic properties are insufficiently understood. We will present an idea how dust devils can be generated in a laboratory experiment and how processes, which contribute to their formation, can be investigated.

We have chosen the so-called Rayleigh-Bénard set-up as an appropriate model experiment for our investigations. The "Barrel of Ilmenau" is a test facility, which consists mainly of an air-filled, cylindrical tank with a total diameter of 7 m and a total height of 8 m. At the bottom of the tank is a heating plate, whose temperature can be set precisely between 20°C and 80°C. A second plate, which can be positioned at any height between 0.2m and 6.3m above the heating plate, is used for cooling and can be set to temperatures as low as 10°C...30 °C. This results in a total temperature difference of up to 70K which is significantly beyond the temperature difference of the atmospheric boundary layer. The side wall of the tank is adiabatic. Due to the isothermal plates and a compensation heating system, a temperature that is constant over time is reached and controlled boundary conditions can be assumed.

For the characterization of Dust Devil-like vortices, an optical measurement method is used to obtain the trajectories of single particles. Since there are no commercial systems that are suitable for such a large measurement volume, we created our own system. The measurements in the RB cell are carried out with an aspect ratio Γ=3 and a Ra number of Ra=2x10¹⁰ and Ra=8x10¹⁰.  With the help of the measurements we want to show that Dust Devil-like vortices are created. The structure should be characterized and the results will be compared to DNS.