Reorientations of a turbulent large-scale convective flow in a cylindrical cell

Long-term numerical simulations of turbulent Rayleigh–Bénard convection of an incompressible fluid with Pr=0.7 in a cylindrical cell of unit aspect ratio and moderate Rayleigh number Ra=108 are performed to analyze the dynamics of reorientations in large-scale circulation (LSC). Special attention is paid to the comparative analysis of the vertical component of the integral angular momentum (mean azimuthal flow) and the characteristics of the LSC, including its intensity, orientation, and angular velocity. Observed rotations of the LSC plane occur either without a significant decrease in LSC intensity, or with cessation of LSC followed by LSC regeneration in a random direction. A pattern common to all reorientations has been revealed—the lower the intensity of the circulation, the higher the angular velocities of the LSC plane rotation. It is shown that the rotation of the LSC plane does not correlate with the mean azimuthal rotation of the fluid, the magnitude of which fluctuates randomly, changing sign. Moreover, unlike the cubic cell, the reorientation is not accompanied by a noticeable increase in the angular momentum. Thus, the reorientation of the LSC in a cylindrical cell is not associated with the azimuthal rotation of the fluid. Furthermore, the characteristics of the LSC follow those of the buoyancy force moment with a short time delay.