DIRECT NUMERICAL SIMULATION OF HEAT TRANSFER MECHANISM IN SEPARATED FLOW

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Direct numerical simulation methodology has been employed to clarify the large scale vortex structure formed in the separated and reattached flow around the surface-mounted rectangular blocks and its correlation with the heat transfer mechanisms. The finite difference method is used to calculate the three-dimensional unsteady Navier-Stokes equations and the energy equation. The fifth-order upwind difference for the space derivative of convection terms is adopted to simulate minutely the detailed flow characteristics. Results obtained are summarized as follows.1. As for the single block, the number of horseshoe vortices formed around it increases from two to six with an increase of Reynolds number.2. In the case of two in-line blocks, the recirculation region extends the whole space between two blocks for small block space. Further, it is found that the horseshoe vortex is not formed around the second block even for a very wide space.3. The flow around two transversal blocks becomes similar to that around a single rectangular block at a very small transversal space, as illustrating a large single horseshoe vortex around them. As the space increases, two horseshoe vortices are formed around each block, they severely interact, and the flow between two blocks is very complicated.4. In the case of staggered three-row blocks, the flow in the neighborhood of the front and side surfaces of the first and second blocks is similar to that of the single block. The horseshoe vortex is formed around the third block only at Re= 500.5. As the Reynolds number increases up to 1000, the unsteadiness of flow becomes severe, as accompanying the shedding of large scale vortices from the blocks.6. These flow structures described briefly above bring about great variations of the heat transfer characteristics around the blocks.