Flow structure in turbulent rotating Rayleigh--B\'enard convection

Turbulent Rayleigh-B\'enard convection is usually studied in an upright cylinder. The addition of axial rotation has profound effects on the flow structuring. The well-known large-scale circulation (LSC) of the non-rotating case is still found at low rotation rates but is replaced by an irregular array of vertically aligned vortical plumes at higher rotation rates. We report PIV measurements of turbulent rotating convection in a cylindrical cell of diameter-to-height aspect ratio $\Gamma=1/2$ at Rayleigh number $Ra=4.5\times 10^9$ and at many rotation rates covering both the LSC and the vortical-plume regime. We focus on: (i) the azimuthal precession of the LSC, (ii) collective motions of the vortical plumes, and (iii) the sidewall boundary layers. With these results we can clarify remarkable differences between the $\Gamma=1$ and $\Gamma=1/2$ cases reported recently in the literature.