  Turbulent Rayleigh-Benard convection in a closed cylindrical cell is studied
in the Lagrangian frame of reference with the help of three-dimensional direct
numerical simulations. The aspect ratio of the cell Gamma is varied between 1
and 12, and the Rayleigh number Ra between 10^7 and 10^9. The Prandtl number Pr
is fixed at 0.7. It is found that both the pair dispersion of the Lagrangian
tracer particles and the statistics of the acceleration components measured
along the particle trajectories depend on the aspect ratio for a fixed Rayleigh
number for the parameter range covered in our studies. This suggests that
large-scale circulations present in the convection cell affect the Lagrangian
dynamics. Our findings are in qualitative agreement with existing Lagrangian
laboratory experiments on turbulent convection.
