Plume motion and large-scale circulation in a cylindrical Rayleigh-Bénard cell

Abstract

We used the time correlation of shadowgraph images to determine the angle $\Theta$ of the horizontal component of the plume velocity above (below) the center of the bottom (top) plate of a cylindrical Rayleigh-Bénard cell of aspect ratio $\Gamma \equiv D/L=1$ ($D$ is the diameter and $L\simeq 87$ mm the height) in the Rayleigh-number range $7\times 10^7\le R\le 3\times 10^9$ for a Prandtl number $\sigma =6$. We expect that $\Theta$ gives the direction of the large-scale circulation. It oscillates time-periodically. Near the top and bottom plates $\Theta (t)$ has the same frequency but is anti-correlated.

4 pages, 6 figures