Confined Swirling Flows of Aqueous Surfactant Solutions Due to a Rotating Disk in a Cylindrical Casing

In this study, confined swirling flows of an aqueous surfactant solution due to a rotating disk in a cylindrical casing were investigated using a sectional flow visualization technique and a two-component laser Doppler velocimetry system. The concentrations of aqueous surfactant solutions $(C14TASal)$ are $0.4wt%$⁠, $0.8wt%$⁠, and $1.2wt%$⁠. Rheological properties such as shear viscosity and first normal stress difference of the surfactant solution were measured with a rheometer. The patterns of secondary flow were classified using the Reynolds and elasticity numbers. We revealed that the projection formed near the center of the rotating disk moved up and down at a constant frequency for $C14TASal$$0.8wt%$ and $1.2wt%$⁠, which has not been reported as far as we know. The effects of the Reynolds number, elasticity number, and aspect ratio on the velocity profiles were clarified. It was also found that the region of rigid body rotation existed at the higher Reynolds number tested for $C14TASal$$0.4wt%$⁠.