Flow structure and heat transport in low Prandtl-number vertical convection

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With joint efforts of the Dresden group (T. Vogt, experimental studies) and the Göttingen group (O. Shishkina, theoretical studies) we are aimed to make a significant progressin understanding of vertical thermal convection in very-low-Prandtl number fluids at large Rayleigh numbers. This type of convection has a great significance for crystal growth processes, the solidification of metal ingots and the application of liquid metals in high-temperature heat exchangers or receivers of concentrated solar power stations and is relevant in convective processes in planetary cores and stellar interiors.Within the complementary experimental and theoretical study, we will mutually verify the Dresden measurements in liquid gallium-indium-tin (GaInSn, Pr ca. 0.03) and the Göttingen Direct Numerical Simulations (DNS) for Prandtl number Pr = 0.03 for intermediate Rayleigh numbers Ra. For higher Rayleigh numbers (Ra at least 2 times 10^9), the Dresden experiments will provide information about the flow fields in form of a certain number of measured linear velocity profiles and the statistical information about the scaling relations with the Rayleigh number Ra of the global heat transport and momentum transport in the system, which are represented, respectively, by the Nusselt number Nu and Reynolds number Re. To attain statistical information in the DNS for very large Ra at such extremely small Pr is difficult due to the necessity to resolve the Kolmogorov microscales on very fine computational meshes. On the other hand, the Göttingen DNS will provide complete information on the velocity and temperature spatial distributions and related flow field characteristics, for similar parameter range as in the experiment. Finally, in Göttingen, the earlier developed boundary-layer model and scaling model for the mean heat and momentum transport in laminar vertical convection will be extended to the turbulent case.