Dresden 2017 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 16: Focus: Fundamental aspects of turbulent convection

DY 16.7: Hauptvortrag

Dienstag, 21. März 2017, 11:30–12:00, ZEU 118

Convection rolls and fingers in double diffusive convection — •Andreas Tilgner — Institute of Geophysics, Göttingen

Double diffusive convection with a stabilizing temperature and a destabilizing salt gradient occurs in large areas in the oceans. Convection is possible even if the net density stratification is stable owing to the very different diffusivities of heat and salt. The typical flow pattern in this case are so called salt fingers. According to some observations, they can organize into layers separated by standard convection rolls. The transport of heat and salt greatly depends on whether fingers form. This contribution will present experiments which used an electrodeposition cell to sustain a destabilizing concentration difference of copper ions in aqueous solution between the top and bottom boundaries of the cell. The resulting convecting motion is analogous to Rayleigh- Bénard convection at high Prandtl numbers if the cell is kept at spatially uniform temperature. However, if a stabilizing temperature gradient is imposed across the cell, double diffusive fingers appear even for thermal buoyancy two orders of magnitude smaller than chemical buoyancy. It is found that the fingers obey several simple scaling laws. The control parameters can also be chosen such that fingers and convection rolls coexist in vertically stacked layers.