Abstract

Many natural flows at high Reynolds or Rayleigh numbers appear in the form of regular patterns at an intermediate range of scales, the mesoscale range. Prominent examples comprise granulation or supergranulation at the surface of the Sun and cloud streets in the atmosphere. In my talk I will present our recent investigation results on the origin of these mesoscale patterns, their dependence on boundary conditions and additional physical processes, such as rotation. I will also discuss the mixing and transport properties in these flows. Our studies are based on 3d high-resolution direct numerical simulations of extended Rayleigh-Bénard convection layers, a paradigm of many natural convection flows. Our simulation studies have been taken recently to very low Prandtl numbers of 0.001 which cannot be obtained in controlled laboratory experiments anymore. The data show here that the fluid turbulence in the bulk of the convection layer is very close to classical Kolmogorov turbulence.