周期的かく乱を伴う３次元ダクト内バックステップ下流の熱流動特性

Abstract

The flow and heat transfer characteristics were investigated by numerically simulating backstep flow in a three-dimensional duct with periodic disturbance to the inlet velocity at moderate Reynolds numbers (Re = 625, 700, and 1000). The periodic disturbance was applied to the approximate equation for a well-developed flow by varying the relative amplitude and forcing frequency. The results show that the reattachment position moves upstream as the disturbance increases. Furthermore, as the Reynolds number increased, the amount of change in the reattachment position due to the disturbance became smaller. This change in the reattachment position was more dependent on the forcing frequency than on the relative amplitude, because the meander spacing of the mainstream narrowed as the forcing frequency increased. The spatiotemporally averaged Nusselt number at each Reynolds number increased by 27.2% when a disturbance was applied, compared to the case where no disturbance was applied. This is due to the fact that the higher the disturbance, the more active the heat exchange becomes not only in the flow direction but also in the height direction, resulting in a higher rate of rise. As with the reattachment position, the amount of change became smaller as the Reynolds number increased. These results suggest that the use of the disturbance can be expected to enhance heat transfer at the lower wall.