2012 Volume 10 Pages 335-340
The addition of very small amounts of flexible polymer to a flow reduces drag in turbulent flow by almost 60% at the maximum. The phenomena has been tried to explain by velocity profile near the wall. Thus, shear strain and shear viscosity gathered much attentions. However, viscoelasticity of polymers that is extensional viscosity should also important to affect fluids. It is said that the extensional viscosity is increased by causing polymer entangled, however, the extensional viscosity should be also increased when the polymer is stretched. In this study, flexible polymer that is easily stretched under strain and naturally stretched rigid polymer are added to the fluids to observe how it effects on turbulent dynamics. For the visualization and single-image analysis of turbulence, our original method - Film Interference Flow Imaging method - is used. Inner structure of sample solution is analyzed by Scanning Microscopic Light Scattering to investigate how polymers expand in fluids. Here, it is assumed that sudden stretch of the flexible polymer in flow cause sudden increase of extensional viscosity, and gradual orientation of the rigid polymer cause gradual increase, which is related to the turbulent drag reduction. Such a fluids control can work not only to improve energy efficiency in industries but also to treat micro fluids in medical area. [DOI: 10.1380/ejssnt.2012.335]
