Fine structures of the convective Taylor columns in rotating Rayleigh-Bénard convection

Under strong rotations, the flow structure in turbulent Rayleigh-Bénard convection is mainly manifested as convective Taylor columns (CTC) traversing the upper and lower boundary layers. We present high-resolution PIV measurements of the fine structures of the CTC in a cylindrical sample over the range of Rayleigh number 2.0×10⁷≤Ra≤8.2×10⁹, Taylor number 5.5×10⁷≤Ta≤7.5×10¹¹ and Prandtl number Pr=4.38. Results of the velocity fields in a horizontal plane show that the azimuthal velocity within the CTC has a universal radial profile V_Φ(r/r₀) with varying vortex radius r₀. Velocity data in vertical planes passing through the vortex centers suggest that the radial dependence of the vertical velocity is dictated by Hankel functions in agreement with pervious theoretical predictions. Our velocity-field data further reveal the vortical-sheath structure surrounding the CTC with its strength dependening on Ta.