This paper focuses on the non-incremental solution of transient coupled non-linear models, in particular the one related to the Rayleigh-Benard flow problem that models natural thermal convection. For this purpose we are applying the so-called Proper Generalized Decomposition that proceeds by performing space-time separated representations of the different unknown fields involved by the flow model. This non-incremental solution strategy allows significant computational time savings and opens-new perspectives for introducing some flow and/or fluid parameters as extra-coordinates. (C) 2012 Elsevier B.V. All rights reserved.