Investigation of the transition of natural convective flow of water in a differentially heated cubic enclosure

The present study aims at the investigation of the transition of the natural convective flow in a water-filled differentially heated cubic enclosure. The schlieren-particle image velocimetry (PIV) system has been developed and employed for simultaneous measurement of ray-averaged velocity and temperature fields from transient schlieren images for distinct Rayleigh number (Ra) (1 x 10(7) <= Ra <= 5 x 10(8)). The experimentally obtained results have been compared with three-dimensional computational results. The three-dimensional incompressible simulations are carried out for a wide range of Ra (1 x 10(5) <= Ra <= 5 x 10(8)), treating the density difference using Boussinesq approximation. The results from present simulations show that the flow is found steady in the range of Ra (1 x 10(5) <= Ra <= 1 x 10(8)) while the critical Ra, at which the steady flow becomes unsteady, lies between 1 x 10(8) and 5 x 10(8). The critical Ra from the experiments is found to lie between 4 x 10(8) and 5 x 10(8). Also, the three-dimensionality effect on large-scale temperature field is found to decrease as Ra increases.