Following a previous study fOr a slender enclosure (AR = 4), direct numerical two-dimensional simulations were conducted for the free convective flow of a low-Prandtl number fluid (Pr = 0.0321) with internal heat generation in a square cavity having adiabatic top and bottom walls and isothermal side walls. The Grashof number, Gr, based on conductive maximum temperature and cavity width, ranged from 10~5 to 10~9. For Gr up to ～10~7, the flow was steady and exhibited left right symmetry. For Gr≈3 × 10~7, the spatial symmetry was broken and asymmetric steady-state flow patterns were obtained. For Gr≈5 × 10~7. the asymmetric flow became time-periodic. Finally, for Gr≥ 10~8, chaotic flow was predicted; the time-averaged velocity and temperature fields were still markedly asymmetric at Gr = 10~8, but reattained bilateral symmetry at higher Gr (10~9), when developed two-dimensional turbulence was observed. For Grashof numbers above ～10~6, the friction coefficient averaged along the vertical walls scaled roughly with Gr~(-1/3) (as in the AR = 4 cavity), while the Nusselt number (overall/conductive heat transfer) increased roughly as Gr~(-1/7), i.e. slightly less markedly than in the slender cavity.
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