Direct numerical simulation of turbulent Rayleigh-Benard convection in mercury

In the present report direct numerical simulations of the Rayleigh-Benard convection in mercury are presented. The simulations complement previous ones, performed for Rayleigh-Benard convection in sodium and air. A particular aim of this study is to investigate if the phenomenon of inertial convection observed in simulations of liquid sodium is also present in mercury. The inertial convection is characterized by large two-dimensional vortices which rotate in a solid body like manner. It is highly efficient in transporting heat by convection. Simulations for mercury (Prandtl number Pr = 0.025) are performed for six distinct Rayleigh numbers in the range 2000 ≤ Ra ≤ 50000. For Ra = 2000, in a numerical study using periodic boundary conditions the influence of the size of the computational domain on the convective pattern is investigated. It is found that physically realistic results for Rayleigh-Benard convection in large aspect ratio containers are only obtained when the periodicity lengths used are sufficiently large. In the simulations with Ra = 2000 no inertial convection is observed. For Rayleigh numbers Ra = 3000, Ra = 6000, and Ra = 12000 the inertial convection is identified in certain time intervals. Its appearance is coupled to regions in which the temperature field is almost two-dimensional. Using results of simulations for mercury, sodium, and air at various Rayleigh numbers, a first step has been undertaken towards the derivation of a regime map for the inertial convection