Flow Characteristics Over a Backward-Facing Step in a Duct in Low Reynolds Number Range

Velocity measurements have been done in order to grasp the flow reattachment locations over a 3D backward-facing step in a duct by PIV for various Reynolds numbers from 200 to 1000. The aspect ratio and the expansion ratio of the stepped duct were 16 and 2, respectively. It was found that the flow reattachment location varies in the spanwise direction in every case. In the range of Re<400, flow near the bottom wall is stable. The longest flow reattachment length appears at the center of the duct while the shortest appears near the side wall. In the range of 400<Re<550, the flow reattachment length turns to be shorten and begins to vary largely near the center of the duct. This variation of the flow reattachment extends to the near wall region around 600<Re<700 and relatively uniform and short flow reattachment is realized in the range of 800<Re. The largest difference in the reattachment length between the center of the duct and near the side wall is generated at Re = 400.