Steady two-dimensional natural convection in fluid filled cavities has been investigated numerically. The conservation equations of mass, momentum and energy governing the motion of a Newtonian Boussinesq fluid have been numerically solved using the finite volume technique. The computations were performed for three cavity height based Rayleigh numbers 104, 105 and 106. In all of the numerical experiments, the channel is heated from below and cooled from the top with insulated side-walls and the inclination angle is varied. The simulations have been carried out for several aspect ratios. For the case of the square cavity the calculated values are in excellent agreement with previously published benchmark results. The effects of the inclination of the cavity to the horizontal, with the angle varying from 0 to 180° and the initial start up conditions were investigated in turn for each aspect ratio. The inclination and the “initial” assumed conditions have a significant effect on the flow patterns, temperature distributions and the heat transfer rates. In particular it is found that the average Nusselt number exhibits discontinuities for rectangular cavities and that the occurrence of the discontinuity with angle of inclination is strongly influenced by the assumed start up field in the steady calculations in much the same way as the hysteresis effect that was identified by other workers.

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