ダクト内バックステップ流れの流動特性と周期性

抄録

Velocity measurements by PIV system have been done for the laminar backward-facing step flow in a duct at the Reynolds number of 400. The aspect ratio and the expansion ratio of the stepped duct were 16 and 2, respectively in this study. Attention was paid to grasp the spanwise variations of both of the instantaneous and the phase-averaged reattachment points and their relationships to the flow structures. The fluid flow characteristics varied in the spanwise direction was confirmed. Near the center of the duct, the fluid flow characteristics changed periodically. The vortices generated periodically and moved toward downstream and then disappeared by redevelopment of flow. Owing to this, the instantaneous reattachment points appeared downstream of these vortices, that is, they appeared upstream, and as time advanced they moved toward downstream, and then new ones appeared upstream. It was also found that the periodicity became weak as it approached from the center to the side wall.