The stability of free convection in an annulus is governed by the boundary conditions on the inner and outer walls of the annulus and the upper and lower boundaries. This paper explores the effect of free convection on the inner surface of the annulus, where the boundary conditions for the outerwall and the upper and lower boundaries are controlled. The temperature is measured in the center of the air cavity and just below the surface of the inner annular boundary. Experimental results are shown for a radius ratio of 0.40, aspect ratio of 20.7. These more recent experimental results are compared to prior work for a radius ratio of 0.60, aspect ratio of 31.0. The results indicate that as the Rayleigh number is increased, the flow experiences a transition from steady flow to a very regular oscillatory flow, and then a supercritical Hopf bifurcation as the flow finally transitions to chaotic behavior. Proper orthogonal decomposition analysis is presented as a method for quantifying the complex dynamic behavior of the system.
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