Turbulent convection in confined and extended domains*

To understand turbulent convection at very high Rayleigh numbers, direct numerical simulations in slender cells are an option. However, the effects of horizontal confinement on the flow properties need to be assessed. We explore the properties of the flow in a slender cylindrical cell of aspect ratio 0.1 for a wide range of Prandtl numbers and compare them with those in an apparatus of aspect ratio 25. We observe similarities in many flow properties — such as the root mean square fluctuations of temperature and velocity, probability distributions of the temperature fluctuation and the kinetic energy dissipation rate — between the confined and extended convection domains. In addition, we estimate the turbulent Prandtl number and find that it varies very similarly with the molecular Prandtl number in both domains.