TED-AJ03-188 NUMERICAL SIMULATION OF UNSTEADY SEPARATED FLOW AND HEAT TRANSFER AROUND AN INCLINED DOWNWARD STEP

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Direct numerical simulation methodology is employed to analyze the unsteady characteristics of a two-dimensional separated and reattached flow and heat transfer around an inclined downward step in a plane channel. Numerical calculations are carried out using the finite difference method. Resulting finite difference equations are solved with a modified HSMAC method. The inclination angle of step α is systematically varied from 15°to 90°, and the Reynolds number Re based on the mean velocity at inlet and the step height from 300 to 2000. The expansion ratio of channel is 2.0 and the Prandt1 number of fluid 0.7,respectively. It is found that the flow is steady at Re≤500 but becomes sensibly unsteady at Re=700. The large scale vortices are formed both on the upper and lower walls and are almost periodically shed to the downstream. These unsteady flow structure brings about the severe fluctuation of temperature in the flow field, resulting in heat transfer enhancement. The time averaged Nusselt number increases with an increase of Re and its increasing rate is great between Re=700 and 900 for all the inclination angles examined. The maximum Nusselt number, in general, increases slightly with α, but its increasing rate is rather small at all the Reynolds numbers[figure]
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