VORTEX FLOW AND THERMAL-CHARACTERISTICS IN MIXED CONVECTION OF AIR IN A HORIZONTAL RECTANGULAR DUCT - EFFECTS OF THE REYNOLDS AND GRASHOF NUMBERS

Abstract

A three-dimensional unsteady numerical simulation was carried out to study the effects of Reynolds and Grashof numbers on the vortex flow structure and thermal characteristics in a buoyancy-induced time periodic mixed convective air flow through a bottom heated horizontal rectangular duct. The unsteady Navier-Stokes equations along with the continuity and energy equations were integrated by the Projection method with the convective and diffusive terms discretized by higher order finite difference schemes. Results for the Reynolds number varied from 1000 to 200 at a fixed Grashof number clearly show the splitting and merging of the longitudinal rolls. The flow destabilizes during the processes of roll merging and splitting. After the merging and splitting the flow gradually stabilizes as it moves downstream. For the Reynolds number at 100, stable thermal stratification appears in the upper half of the duct and the flow oscillation is significantly suppressed there.