C301 EFFECTS OF SIDE-WALL TEMPERATURE ON THE FLOW PATTERN OF RAYLEIGH-BENARD CELLS IN AN ENCLOSURE : GEOMETRY OF ENCLOSURE: 6:4:1(Mixed convection)

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Experimental and numerical studies concerning the effects of side-wall temperature on the flow pattern and the transition to turbulence of Rayleigh-Benard cells in a rectangular enclosure with an aspect ratio of 6:4: 1 are presented. Experiments were carried out using air with several Rayleigh numbers (Ra) up to 32,000. I found that at Ra=8000 there appear three steady flow patterns consisting of the following: four transversal roll cells, two cells, and two longitudinal roll cells. At Ra ≈ 8200, the pattern consisting of two longitudinal roll cells begins to exhibit time-dependent sinuous oscillatory flow. The resulting sinuous oscillation takes the form of a standing wave. Further increasing Ra results in a series of successive subharmonic bifurcations and eventually chaos. Furthermore, it was found that the dependence on Ra of the peak oscillatory frequency f_l changes at Ra=20,000 due to a change of the dynamical mode in the two oscillatory roll cells. Both the two-cell pattern and the two longitudinal roll-cell pattern undergo a series of successive subharmonic bifurcations, but the change in the spatial structure exhibited by each through these bifurcations are quite different.
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2000-10-01