The onset of two-dimensional convection with strongly temperature-dependent viscosity has been considered for a fluid obeying an Arrhenius law. The critical Rayleigh number Rc and the basic features of the flow field at criticality have been identified based on a linear stability analysis. Convective flow patterns near and beyond criticality have been determined based on a direct numerical simulation. It is shown that, as the Rayleigh number R increases beyond Rc, steady rolls first emerge supercritically and that at sufficiently large values of R there is a secondary Hopf bifurcation corresponding to pulsating cells; the peculiar structure of the flow field in each case has been described.
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