On thermally induced separation of laminar free-convection flows

The influence of a short cooled wall region on the laminar free-convection flow along a semi-infinite constantly heated vertical flat plate is investigated in the limit of large Grashof number. A double-deck structure is shown to emerge in an asymptotically correct description of the flow. Two different flow regimes have to be distinguished depending on the spatial extent and the intensity of cooling. For short-scale, strong disturbances we present a numerical investigation of the resulting interaction problem as well as analytic solutions of a linear perturbation analysis. For disturbances which are longer and weaker compared to interaction scales the phenomenon of marginal separation comes into play and the lower and upper decks can be treated independently. In this case the field quantities can be described by regular asymptotic expansions which are found to be in good agreement with a numerical solution of the boundary-layer equations. (C) 2001 American Institute of Physics.