Exploring Thermo-Electrohydrodynamic Flows with DifferentialRotation in AtmoFlow

The AtmoFlow experiment is a small-scale,  laboratory experiment  designed to explore idealized large-scale atmospheric flow fields and planned to become operational onboard the International Space Station by 2026. The experiment is composed of two independently rotating spherical shells, mimicking planetary rotation. The temperature on the shell's boundaries is heated at the equator and cooled at the poles to count for the equatorial and polar temperature difference in the presence of solar radiation. An electrical field is applied to a dielectric fluid confined between the shells that serves as an artificial gravity force, known as dielectrophoretic force, inducing the formation of buoyant flow patterns.

Beyond modelling terrestrial or explanatory atmospheres via solid body rotation, the experiment is also able to mimic atmospheric regimes of large celestial bodies by deferential rotation of each shell. The resulting combination of rotational momentum flux and buoyancy force gives rise to distinctive patterns that are dependent on the magnitude of the forcing parameter, enabling to study different regimes. Prior studies have shown that the electric gravity gives rise to a buoyant force leading to plume-like patterns [1,2] in the radial direction, while the Taylor vortices induced by differential rotation maintains an azimuth flow component. The main objective of this study is to investigate the interaction between these two different transport mechanism.

Complementing numerical investigations are therefore performed to model the experiment using the OpenFOAM ecosystem, an open source finite volume solver.  The emerging convective regimes close to the outer shell regions are evaluated. The observed patterns are the classified into these distinct regimes  and presented in a regime diagram showing the transition from different convective states. 
Beside the pattern analysis, the heat flux through the model is investigated in relation to the forcing strength. This provided  an estimation of the overall heat transported from the inner to the outer shell.  The changes in the thermal transport were also reflected in the kinetic energy, which was monitored for each case and brought in relation to the evaluated heat transfer.

[1] Futterer, B., R. Hollerbach, and C. Egbers, ‘GeoFlow: 3D Numerical Simulation of Supercritical Thermal Convective States’, Journal of Physics: Conference Series, 137/1 (2008), 012026

[2] Futterer, B., A. Krebs, A.-C. Plesa, F. Zaussinger, R. Hollerbach, D. Breuer, and others, ‘Sheet-like and Plume-like Thermal Flow in a Spherical Convection Experiment Performed under Microgravity’, Journal of Fluid Mechanics, 735 (2013), 647–83