A DIRECT NUMERICAL-SIMULATION OF TRANSITION IN MIXED CONVECTION FLOWSBETWEEN 2 HEATED PARALLEL PLATES

This paper seeks to increase our understanding on the fluid mechanics and heat transfer in a transitional mixed convection flow between two vertical plates. Direct numerical simulation by the spectral method, w ith a weak formulation, is used to solve the transient 3-D Navier-Stok es equations and energy equation. Initial disturbances consist of the finite-amplitude 2-D Tollmien-Schlichting wave and two 3-D oblique wav es. The transition phenomena in a mixed-convection flow can be signifi cantly different from the isothermal flow. Disturbance competitions am ong different modes are also found to be different from those known fo r an isothermal flow. In a mixed-convection flow, there exist threshol ds for the low-mode Fourier. waves. The intensified vortices are conce ntrated left of the central surface between the two plates. Hairpin vo rtices are formed with high Ri. Based on the flow visualization, the l ambda vortices are found to be staggered on the surfaces parallel to t he plates. The Ri number seems to be the main parameter governing the transition mechanism. The Nu number is found to increase during transi tion.