We present a numerical study of double-diffusive convection characterized by a stratification unstable to thermal convection, while at the same time a mean molecular weight (or solute concentration) difference between top and bottom counteracts this instability. Convective zones can form in this case either by the stratification being locally unstable to the combined action of both temperature and solute gradients or by another process, the oscillatory double-diffusive convective instability, which is triggered by the faster molecular diffusivity of heat in comparison with that one of the solute. We discuss successive layer formation for this problem in the case of an instantaneously heated bottom (plate) which forms a first layer with an interface that becomes temporarily unstable and triggers the formation of further, secondary layers. We consider both the case of a Prandtl number typical for water (oceanographic scenario) and of a low Prandtl number (giant planet scenario). We discuss the impact of a Couette like shear on the flow and in particular on layer formation for different shear rates. Additional layers form due to the oscillatory double-diffusive convective instability, as is observed for some cases. We also test the physical model underlying our numerical experiments by recovering experimental results of layer formation obtained in laboratory setups.
Double-diffusive convection Layering Stability
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F. Kupka gratefully acknowledges financial support through Austrian Science Fund (FWF) Projects P 25229-N27 and P 29172-N27. The numerical simulations have been performed on the Vienna Scientific Cluster VSC (Project 70708), resources dedicated to the Faculty of Mathematics at VSC-3. We thank M.H. Montgomery for providing us with computational resources at the TACC Stampede2 cluster (University of Texas, Austin).
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Conflict of interest The authors declare that they have no conflict of interest.
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