RÉSUMÉ

A numerical study of mixed natural and forced convective flow over a thin vertical flat plate which has a uniform surface heat flux has been undertaken. Attention has been restricted to the case where the buoyancy forces act in the opposite direction to the forced flow, i.e., to opposing mixed-convective flow. Laminar, transitional, and turbulent flow situations have been considered and the development of unsteady flow has been allowed for. The forced flow has been assumed to be steady and the Boussinesq approach has been used. The solution has been obtained by numerically solving the governing equations using the commercial CFD solver, ANSYS FLUENT_© . The k-epsilon turbulence model with the full effect of buoyancy forces accounted for and with standard wall functions has been used in obtaining the solutions. The heat-transfer rate from the surface of the plate has been expressed in terms of the mean Nusselt number based on the overall plate length and the difference between the overall mean plate temperature and the undisturbed fluid temperature. This Nusselt number depends on the values of the heat flux Rayleigh number based on the plate length, the Reynolds number based on the plate length, and the Prandtl number. Results have been obtained for a Prandtl number of 0.74, i.e., essentially for the value for air. The conditions under which the flow can be assumed to be purely forced convective and under which the flow can be assumed to be purely natural convective, in particular, have been investigated.