PRESSURE-GRADIENT EFFECT IN NATURAL-CONVECTION BOUNDARY-LAYERS

The high Grashof number laminar natural convection flow around the low er stagnation point of a symmetric bowl-shaped heated body is analyzed . A region is identified where the direct effect on the flow of the co mponent of the buoyancy force tangential to the body surface is compar able to the indirect effect of the component normal to the surface, wh ich acts through the gradient of the nonuniform pressure that it induc es in the boundary layer. Analysis of this region provides a descripti on of the evolution of the flow from a pressure-gradient dominated reg ime to a buoyancy dominated regime. Numerical results are presented fo r the flows above and below heated power-law body shapes, and the upst ream propagation of small perturbations to the stationary flow is disc ussed. An asymptotic analysis is carried out for the flow below nearly flat horizontal bodies, for which the change from pressure-gradient-d riven to buoyancy-driven flow occurs very rapidly in a short region. T he influence of body edges located in the region of interest is also d iscussed.