Three-Dimensional Analysis of Flow and Heat Transfer of Thermal Plume in Stably Stratified Ambient (Flow Field)

The flow field of a three-dimensional, time-dependent thermal plume in stably stratified ambient above a heated square plate was elucidated by solving numerically governing equations. Phenomena characterizing this plume are as follows : (a) Velocity vectors on a horizontal plane above the heated plate have a X-shape distribution at any stratification. (b) The local Nusselt number distribution on the plate was affected by the X-shape distribution. (c) In Velocity vectors on the vertical plane, a V-shape occurred near the plate, and a horizontal imterface occurred between inward and outward flows. Time-dependency in the plume is resulted from instability near the front with negative buoyancy, and became weak with increasing stratification. At the extremely strong stratification, flow became steady state. The flow at strong stratification differed clearly from that at medium stratification as follows : At the medium stratification, the upward flow interfered with the stratified air, and a Π-shape of the velocity vector distribution occurred near the front. However, at strong stratification, the stratification effect is more dominant than the upward flow effect, and a Λ-shape occurred. With increasing stratification, the flow velocity near the plate became small, and the mean Nusselt number decreased.