Polymer drag reduction below and above the overlap concentration

Abstract

We study the polymer drag reduction (DR) for a range of concentrations below and above the overlap concentration in a Taylor–Couette geometry. We use three kinds of polymers, two flexible (polyacrylamide and polyisobutylene) and one rigid (diutan gum). It is largely known that an increasing concentration accelerates the onset of DR, but it seems that this is true only for diluted solutions. We show that for concentrated solutions, the opposite can occur. Our data also suggest that maximum drag reduction asymptote can be overpassed when one uses solutions with concentrations above the overlap concentration. We attribute this extra DR to polymer aggregation, which is more frequent in more concentrated solutions.