Boundary layer flows in a vertical porous enclosure induced by opposing buoyancy forces

Double diffusive natural convection induced in a vertical porous layer subj ect to opposing horizontal gradients of heat and mass is studied analytical ly and numerically using the Darcy model with the Boussinesq approximation. The governing Parameters for the problem are the thermal Rayleigh number, R-T, the Lewis number, Le, the buoyancy ratio, N and the aspect ratio, A, o f the enclosure. The analytical solution is developed on the basis of the p arallel flow approximation. A numerical study is performed to validate the results of the analytical predictions. It is demonstrated in this study tha t there exists a domain in (Le, N) plane where, at large R-T, boundary laye r profiles are obtained for the velocity and density but not for the temper ature and concentration. The boundary layer regimes obtained for this domai n (N < 0) are extremely different from those found in the previous studies for the case of aiding buoyancy forces (N > 0). (C) 1999 Elsevier Science L td. All rights reserved.