Drag Reduction in Turbulent Flow of Polymer Solutions

Progress in understanding turbulent drag reduction by polymer additives has recently been made on several fronts. The near-wall dynamics of Newtonian turbulence is becoming better understood. Detailed computations of complex flows of model polymer solutions are now possible. Insights into the effects of viscoelasticity have been gained from a number of important model flows, and the understanding of the dynamics of dilute polymer solutions, as well as the ability to perform detailed simulations of them, is maturing. We review the advances in these fronts and illustrate their contributions to the understanding of both turbulence and drag reduction. Finally, we highlight open questions and propose a general conceptual framework that would, if validated, unify observations of drag reduction from turbulence onset to the maximum drag reduction asymptote.