Rotating turbulent thermal convection at large Rayleigh numbers

• Applicants: Privatdozentin Dr. Olga Shishkina; Dr. Stephan Weiss
• Subject Area: Fluid Mechanics
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 324106305

With the proposed project we will study rotating turbulent Rayleigh-Benard convection (RBC) at very large Rayleigh numbers Ra by complementary efforts from experiments and numerical simulations. While we measure accurately the convective heat transport in the experiment for Ra up to 1e15, the simulations provide any desired level of detail about the internal flow structure. In order to reach such high Ra experimentally, we will use compressed sulfur hexafloride at up to 19 bar as the convecting fluid, resulting in a Prandtl number (Pr) of about 0.8. The maximal rotation rate as expressed by the inverse Rossby number (1/Ro) will be about 20. One of the primary investigations considers the influence of rotation on the transition to the ultimate RBC state. As the ultimate state is assumed to prevail for diverging Ra, we expect a reasonable extrapolation of our laboratory results to the geo- and astrophysically relevant ranges of Ra and 1/Ro. Another primary investigation will address the heat transport and the flow structure in the geostrophic regime. That is the regime at very high Ra and 1/Ro when pressure gradients are balanced by Coriolis forces, which is dominant in the earth's atmosphere.Direct Numerical Simulations (DNS) will be conducted for Ra up to 1e11 with the same geometry of the convection cell, the same 1/Ro-range, and similar Pr as in the experiment. In the numerical investigations, we in particular want to study the structure and dynamics of the Ekman and Stewartson boundary layers, the global flow structures and their close connection to the toroidal-poloidal energy balance, and the velocity and temperature fluctuations. Also with the numerics, we aim to explore the regime of geostrophic turbulence. In fact there is a region in the parameter space, for Ra from 1e9 to 1e11 and 1/Ro from 0.02 to 20, where experiments and DNS overlap, and where at least in some parts geostrophic conditions are expected. With the complementary efforts from both experiment and numerics, we will significantly contribute for a better understanding of the flow field and the heat transport properties in rotating RBC in this regime.

• DFG Programme: Research Grants