2010 年 76 巻 761 号 p. 4-10
Confined swirling flows of aqueous polymer solutions due to a partially rotating disc in a cylindrical casing have been investigated using a flow visualization technique. The ratio of rotating disc radius R_d to container radius R_c, σ=R_d/R_c, was 0.4, 0.6 and 1.0. As the aqueous polymer solution, 0.5, 0.8 and 1.0wt% polyacrylamide (PAA) solutions were used. It was observed that at σ=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 σ=1.0. Regardless of σ, the period of the vortex shedding seemed to increase with the Reynolds number Re_0. The diameter of the ring vortex B, which increased with the increase of Re_0, was roughly between 0.2 and 0.4 times the outer diameter of the rotating disc. Regardless of C or σ, the height of the vortex h was about 0.1 times the diameter of the rotating disc. The relation between the lower-critical Reynolds number for the ring vortex (Re_0)_c and the elastic number E_0 could be expressed by the equation, (Re_0)_c=10E_0^<-3/5> which was independent of σ.