Inclined turbulent thermal convection in liquid sodium

Inclined turbulent thermal convection by large Rayleigh numbers in extremely small-Prandtl-number fluids is studied based on results of both, measurements and high-resolution numerical simulations. The Prandtl number $Pr\approx0.0093$ considered in the experiments and the Large-Eddy Simulations (LES) and $Pr=0.0094$ considered in the Direct Numerical Simulations (DNS) correspond to liquid sodium, which is used in the experiments. Also similar are the studied Rayleigh numbers, which are, respectively, $Ra=1.67\times10^7$ in the DNS, $Ra=1.5\times10^7$ in the LES and $Ra=1.42\times10^7$ in the measurements. The working convection cell is a cylinder with equal height and diameter, where one circular surface is heated and another one is cooled. The cylinder axis is inclined with respect to the vertical and the inclination angle varies from $\beta=0^\circ$, which corresponds to a Rayleigh-B\'enard configuration (RBC), to $\beta=90^\circ$, as in a vertical convection (VC) setup. The turbulent heat and momentum transport as well as time-averaged and instantaneous flow structures and their evolution in time are studied in detail, for different inclination angles, and are illustrated also by supplementary videos, obtained from the DNS and experimental data. To investigate the scaling relations of the mean heat and momentum transport in the limiting cases of RBC and VC configurations, additional measurements are conducted for about one decade of the Rayleigh numbers around $Ra=10^7$ and $Pr\approx0.009$. With respect to the turbulent heat transport in inclined thermal convection by low $Pr$, a similarity of the global flow characteristics for the same value of $RaPr$ is proposed and analysed, based on the above simulations and measurements and on complementary DNS for $Ra=1.67\times10^6$, $Pr=0.094$ and $Ra=10^9$, $Pr=1$.