Spin-Up of a Convection Cell

Experimental setup

A cylindrical Rayleigh-Bénard convection cell, initially in a state of turbulent convection, is subjected to impulsive spin-up about its vertical axis. The final state of the cell is that of rotating turbulent convection at a constant rotation rate.
Water filling the cell is seeded with thermochromic liquid crystals that change their color with temperature. By illuminating a horizontal section near the top of the cell with a sheet of white light, we visualize instantaneous temperature maps of the flow.
During the transient period before the final state is reached, azimuthally regular structures form within the cell. Depending on the final rotation rate, we observed one to three concentric rings of cold downwelling flow. As the flow evolves, Kelvin-Helmholz vortices roll up in the rings, destroying them. The initial pattern of vortices is regular, but soon it loses its regularity, completing the transition to the state of rotating turbulent convection.
The number of rings increases with the final rotation rate of the cell. The radii of the rings are only weakly dependent on the rotation rate and temperature difference between the top and the bottom of the cell. The first ring always has a radius r ~ 3/4 r₀