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 investi gated in the limit of large Grashof number. A double-deck structure is show n to emerge in an asymptotically correct description of the flow. Two diffe rent flow regimes have to be distinguished depending on the spatial extent and the intensity of cooling. For short-scale, strong disturbances we prese nt a numerical investigation of the resulting interaction problem as well a s analytic solutions of a linear perturbation analysis. For disturbances wh ich are longer and weaker compared to interaction scales the phenomenon of marginal separation comes into play and the lower and upper decks can be tr eated 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 Ins titute of Physics.