Structure and Dynamics of Large-Scale Circulation in Turbulent Convection at High Prandtl Numbers

The structure and dynamics of the large-scale circulation in turbulent Rayleigh—Benard convection in a cubic cell are experimentally investigated for fluids with moderate and high Prandtl numbers (from 3.5 to 64). The decomposition of two-dimensional velocity fields into Fourier modes shows that with variation of the Prandtl number from 3.5 to 24 one large-scale mode predominates in the flow. With further increase in the Prandtl number the flow structure considerably changes and the energy is redistributed between several lower Fourier modes. The temporal dynamics of the predominant mode is also considerably changed.