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 coo led along the vertical walls and solutal gradient is imposed vertically. Th e objective of the work is to identify the flow regime for thermal and solu tal dominated flows. It is found that the flow becomes unstable (oscillator y) for finite range of solutal to thermal buoyancy ratios. It is possible t o obtain different solutions on this region depending on the initial condit ions. Also, the results reveal that the thermal convection may be suppresse d for strongly stratified fluid. Owing to the large number of parameters, t he results are reported for aspect ratio of two, Prandtl number of 7.0 (wat er) and Lewis number of 100 (aqueous solution). Rayleigh number is varied b etween 7 x 10(3) and 7 x 10(5). (C) 2001 Editions scientifiques et medicale s Elsevier SAS.