关键词: Langevin方程
, Rayleigh-Bénard 对流, 扩散

Abstract: The trajectories of fluid particles and Brownian particles in a twodimensional
periodic RayleighBénard convection are investigated by assuming a streamfunc
tion with freestress boundary conditions. It is shown that fluid particles ori
ginally located in the central of the cell move periodically, whereas those orig
inally located at the edge of the cell move in a chaotic way. The length of cent
ral region of the cell decreases with the increasing oscillation amplitude and S
trouhal number. The movement of Brownian particles can be either periodic or cha
otic from whichever region the particles originate. The diffusion for both fluid
particles and Brownian particles is standard diffusion at large time of particl
es being released.

Key words: diffusion, Langevin equation
, Rayleigh-Bénard convection