Abstract
The flow around a circular cylinder in surfactant solution was investigated experimentally by measurement of the drag in the Reynolds number range 500 < Re < 6,000. The experiments were performed in a vertical re-circulating water tunnel. The drag coefficient was measured by the apparatus, which could measure the drag acting on the circular cylinder directly. Three cylinders of diameter d=10,19 and 25mm were tested, the ratio of length to diameter was (l/d)=11.2. Test surfactant solution was aqueous solution of Ethoquad O/12 (Lion Co.) at concentrations of 200ppm, and sodium salicylate was added as a counterion. It was cleared that the drag coefficient of a circular cylinder in surfactant solution larger than that in tap water at the Reynolds number range 500 < Re < 4,000. The value of the drag coefficient in surfactant solution was dependent on not only (l/d) but also cylinder diameter. According to the increase of the Reynolds number, the drag coefficient decreased by (Re)^<-3/2>. On the other hand, the value of the drag coefficient in surfactant solution became smaller than that in tap water at Re≅5,000.
