Convection Diffusion in Hexagonal Rayleigh-Bénard Cell

Abstract

A study is made on the diffusion of particles in the thermal convection in a horizontal fluid layer, which is slightly above the critical Rayleigh number. In our experiment, in which almost periodic array of hexagonal cells is generated, a star-shaped spreading of neutrally buoyant particles is observed. Numerical simulation is performed, by taking a spatially periodic regular array of steady laminar hexagonal Rayleigh-Benard cells as a basic flow, into which particular types of small disturbances are applied. Horizontal distribution of advected particles, particle paths and effective transport coefficient are investigated for various amplitudes, directions and frequencies of the perturbation. The characteristic pattern of impurity is reproduced in laminar hexagonal-cell-like flow with zero mean velocity, with enhanced effective transport coefficient which is proportional to the perturbation amplitude and which becomes maximum at some resonant frequency.