FLOW STRUCTURES AND HEAT-TRANSFER DURING TRANSITION IN PERTURBED MIXED-CONVECTION CHANNEL FLOWS

This research seeks to increase our understanding of fluid mechanics a nd heat transfer phenomena in transitional mixed-convection flows betw een two heated vertical plates. A direct numerical simulation by the s pectral method with weak formulation is used to solve the transient th ree-dimensional (3-D) Navier-Stokes equations and energy equation. ini tial disturbances consist of the finite amplitude two-dimensional Toll mien-Schlichting wave and two 3-D oblique waves. The Nusselt number (N u) is mainly a function of the Rayleigh number (Ra) and also depends o n the Reynolds number (Re) and the Richardson number (Ri). Nu dependen ce on Re increases with increase of Ra. Disturbance competitions among different modes during transition are shown for different sets of dim ensionless parameters. Flow visualization by passive particles is also presented.