The stability of the flow of drag-reducing solutions such as polymer solutions and surfactant solutions between concentric cylinders with the outer cylinder rotating and the inner one at rest has been investigated by mean of flow visualization. Two kinds of polymer solutions and a surfactant solution are used, all of which show remarkable drag reduction in the turbulent region. Critical Reynolds number at which turbulence appears decreases with an increase in the concentration of additives. Appeared turbulence was not spiral turbulence observed in the case of water but large scale one in the case of polymer solutions and dislocated Taylor vortex like pattern in the case of surfactant solution. It is found that surfactant solution shows remarkable hysteresis at critical value, whereas it is not so remarkable in the case of polymer solutions.
