Transient natural convection in an enclosure with horizontal temperature and vertical solutal gradients

Transient, double diffusive natural convection in a horizontal enclosure is investigated numerically and analytically. The enclosure is heated and cooled along the vertical walls and solutal gradient is imposed vertically. The objective of the work is to identify the flow regime for thermal and solutal dominated flows. It is found that the flow becomes unstable (oscillatory) for finite range of solutal to thermal buoyancy ratios. It is possible to obtain different solutions on this region depending on the initial conditions. Also, the results reveal that the thermal convection may be suppressed for strongly stratified fluid. Owing to the large number of parameters, the results are reported for aspect ratio of two, Prandtl number of 7.0 (water) and Lewis number of 100 (aqueous solution). Rayleigh number is varied between 7 x 10(3) and 7 x 10(5). (C) 2001 Editions scientifiques et medicales Elsevier SAS.