Abstract
A drag reducing flow was investigated for dilute cationic surfactant solutions in a rectangular channel. Laser sheet scattering due to micelles and shear induced structure (SIS) was observed for the channel cross section. If the Reynolds number was low, uniform scattering due to micelles was observed over the cross section. Increasing in the Reynolds number, the scattering became heterogeneous, and the dark sheet-like or thread-like SISs appeared on the cross section. The sheet-like SISs were observed upstream at a low Reynolds number. On the other hand, the thread-like SIS were observed downstream at a high Reynolds number. The dark SISs had gel-like elasticity, and the darkness was suggested to be due to their transparency.
