Effects of Sidewall Temperature on the Flow Pattern and the Bifurcation to Chaos of Rayleigh-Benard Cells in an Enclosure : Aspect Ratio of Enclosure: 6:4:1

Experimental and numerical studies relating to the effects of sidewall temperatures on the flow pattern and the bifurcation to chaos of Rayleigh-Benard cells in a rectangular enclosure with a length : width: height aspect ratio of 6:4:1 are presented. Experiments were carried out using air with several Rayleigh numbers (Ra) of up to 32000. At Ra=8000 there appear three steady flow patterns consisting of the following : four transversal rolls with axes parallel to the short sidewalls, two cells, and two longitudinal rolls with axes parallel to the long sidewalls. At Ra=8200, the pattern consisting of two longitudinal rolls begins firstly to exhibit time-dependent sinuous oscillatory flow among three steady flow patterns. The resulting sinuous oscillation takes the form of a standing wave. Further increase of Ra results in a series of successive subharmonic bifurcations and eventually chaos. Furthermore, it was found that the dependence on Ra of the peak oscillation frequency f_1 changes at Ra=20000 due to a change of the dynamical mode in the two oscillatory rolls. Both the two-cell pattern and the two-longitudinal-roll pattern undergo a series of successive subharmonic bifurcations, but the changes in the spatial structure exhibited by each through these bifurcations are quite different.