Numerical study of 3D nonlinear disturbance growth in transitional natural convection

Three dimensional boundary layer disturbance growth in natural convection adjacent to a uniformly heated vertical plate has been studied using a finite volume direct numerical simulation (DNS). The sequence of events associated with the intermediate stage of the spatial laminar-turbulent-transition for water, with Prandtl number Pr = 6.7, for the Rayleigh numbers in the range Ra _x ≈ 1 × 10 - 4 × 10¹³, with perturbation parameters closely matching the experiment reported in [1], is investigated. Preliminary calculations confirm that this stage is characterized by the development of spatially periodic inner and outer span-wise vortices (shear layers), which travel in a differing fashion and speed; and a secondary mean flow system. The important route to natural convection flow breakdown, the arising of a double vortex mean longitudinal system, repeatedly suggested by past experiments, seems to be related to the complex and opposing behavior of these two layers.