Vortex shedding in confined swirling flows of polymer solutions with a partially rotating disc

Confined swirling flows of aqueous polymer solutions due to a partial rotating disc in a cylindrical casing have been investigated using a flow visualization technique and a PIV measurement. The ratio of rotating disc radius R-d to container radius R-c, sigma = R-d/R-c, was 0.4, 0.6 and 1.0. As the aqueous polymer solution, 0.5, 0.8 and 1.0 wt% polyacrylamide (PAA) solutions were used. It was observed that at sigma = 0.4 and 0.6, the ring vortex was formed near the partial rotating disc and it was shed periodically for all the solution concentrations C tested, as well as at sigma = 1.0. The width of the ring vortex B, which increased with the increase of Reo, was roughly between 0.2 and 0.4 times the outer diameter of the rotating disc. Regardless of the C or sigma, the height of the vortex h was about 0.1 times the diameter of the rotating disc. It was found that the relation between the lower-critical Reynolds number for the vortex shedding (Reo), and the elastic number E-0 could be expressed by the equation, (Re-0)(c) = 10 E-0(-3/5), which was independent of the sigma.