Velocity Fields around the Bulge Structure Observed in a Cavity Swept by a Visco-Elastic Fluid

Abstract

In order to clarify the mechanism of the bulge structure appearance observed in a cavity swept by a visco-elastic fluid, velocity fields were measured by a two-dimensional particle image velocimetry (PIV). The rib height, the cavity length, the flow path height and the flow path width were fixed at 20 mm, 100 mm, 40 mm and 75 mm, respectively. The Reynolds number was also fixed at 1,700 where the bulge structure appeared as reported by the previous study. The spanwise positions of the two-dimensional PIV were changed in 6 steps from the center plane to the outer region. From the results, it was found that the bulge structure has high-level fluctuation and its intermittency is related to the longest relaxation time. The bulge structure appears when the main flow separated from the upstream top corner of the cavity is intensified. The separated main flow contracted in the former cavity region expands not only toward the cavity bottom but also toward the outside walls of the flow path. In order to supply the fluid in the center plane, the backward flow occurs in the cavity. This flow motion was concluded to be a basic mechanism of the bulge structure appearance.