ABSTRACT
We present a visualization study of turbulent convection in gas under pressure for Rayleigh numbers (Ra) from 5 x 105 to 1 X lOll, with Prandtl number Pr = 0.7. Measurement of the thermal boundary layer thickness indicates that it scales as Ra-2 / 7 for Ra > 2 x 107 . Here we present shadowgraph images of the flow near the boundary layers for a cubic cell with L = 17 em. We study the plumes and other structures which form above the thermal layer and are advected horizontally in the large scale circulation which persists in the cell. Measurements of the two-point intensity correlation function of these images provide quantitative information: the average size and penetration length of the plumes into the bulk of the cell (the development height zc). The dependence of these new lengths on Ra indicates that the high Reynolds shear of the large scale circulation is modifying the dynamics near the plates.
