Abstract
Predictions of drag reduction based on the coherent fine scale eddy in near-wall turbulence are presented. To develop the prediction method of the drag reduction, time scale ratio of drag reducing additives like surfactants to coherent fine scale eddy is introduced. This time scale ratio characterizes the range of drag reduction for pipes of different diameters. Drag reduction of 65% is achieved in straight pipes and 30% in a curved pipe, and the ranges of drag reduction in each pipe of same diameter depend on the concentration of surfactants.
