This study presents a numerical analysis of the dynamics of transitional natural convection flow regimes, generated by a confined thermal source. The system considered is a 2D enclosure of square cross-section, containing a horizontal cylindrical source, placed in a central position. The heat carrier fluid is air with Prandtl number Pr = 0.7. The resulting flow is investigated with respect to the variation of the Rayleigh number, based on the minimum gap width H between the cylinder and the enclosure walls. Three values of the aspect ratio A are considered (A = 2.5, 3.3, 5). The first bifurcation of the low-Ra fixed-point solution is tracked for each A-value. The transition to unsteady, chaotic flow is detailed for A = 2.5. The supercritical behaviour of the system is investigated using nonlinear analysis tools and phase space representations of the computed time series.

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