Thermal convection (Rayleigh-Bénard)

One of the classical thermal convection systems is the Rayleigh-Bénard setup: a fluid in a container heated from below and cooled from above.

Figure 1: Schematic drawing of a Rayleigh-Bénard cell. The red-shaded areas of the cell show regions of hot fluid, while the blue areas indicate cold fluid. Adapted from L. Kadanoff, Physics Today 54, 34 (2001).

In the turbulent regime, the flow is characterized by a large-scale circulation (LSC) with temperature and velocity fluctuations on smaller scales and near the boundaries of the container kinetic and thermal boundary layers are formed. Figure 1 shows an schematic overview of the flow structure that is formed. The control parameters are the fluid properties, the container geometry, and the strength of the temperature gradient, or, in dimensionless form, the Prandtl-number Pr, the Rayleigh number Ra, and the aspect ratio G. The response of the system can be expressed as the dimensionless heat flux (Nusselt number Nu) and the dimensionless strength of the turbulence (Reynolds number Re). The rotation speed of the system is definened by the Rossby number (Ro), which is the inverse rotation rate.

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