Impacts of geometric parameters on bulge structure appearance in a cavity swept by a visco-elastic fluid

We previously reported a bulge like flow structure is formed in a cavity swept by a visco-elastic fluid. In this study, effects of geometric parameters of the cavity on the bulge structure appearance have been investigated by flow visualization. As visco-elastic fluids, cationic surfactant aqueous solutions were treated with counter-ion suppliers of sodium salicylate. The molar ratios of sodium salicylate to cationic surfactants, oleylbishydroxyethylmethyammonium chloride, were changed from 1.5 to 10. The geometric parameters were also changed. The cavity depth, the wide flow path and the cavity length raged from 5 to 30 mm, from 25 to 40 mm and from 50 to 100 mm, respectively. From the results, three kinds of flow regimes were observed; 1. simple separation and reattachment occurrence, 2. bulge structure appearance and 3. recirculation region covering the cavity. In the cases when the molar ratio is high, bulge structure was not found to appear. When the aspect ratio of the narrow flow path was high, the flow also transited directly from 1 to 3 of the above flow regime. This flow regime was concluded to relate to the Deborah number of fluids.