摘要：The objective of this study is to clarify the flow characteristics of drag-reducing flow and to elucidate the mechanism underlying this phenomenon. The surfactant and counter ion we used were Lipothoquad O/12 and sodium salicylate, respectively. The drag reduction rate (DR%) was measured by using a recirculating system with a diameter of 25.6 mm. We also measured the flow characteristics of the surfactant solutions with different concentrations and temperatures by using particle image velocimetry (PIV). From the experimental results,DR% at an average velocity of 2.0 m/s increased from 0 to 68% as the temperature increased from 10 to 40 °C at a constant concentration of surfactant (300 mg/L). From the velocity contour plot obtained from PIV, we found that the thickness of the lower-velocity region of the drag-reducing flow near the pipe wall was thick at 20 °C, whereas vortex motions seemed controlled at 30 °C. On the other hand, the lower-velocity region thickened as the concentration of the surfactant increased at 25°C. Even if the same level of drag-reducing effects occurred, the flow patterns were quite different depending on the concentration and temperature.
