Eur. Phys. J. E (2018) 41: 146
https://doi.org/10.1140/epje/i2018-11751-3

Regular Article

Turbulent viscosity profile of drag reducing rod-like polymers

¹ Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands
² Laboratoire d’Ingénierie des Systèmes de Versailles (LISV), 10/12 Avenue de l’Europe, 78140, Velizy, France
³ LUSAC, University of Caen Normandy, 60 Rue Max Pol Fouchet, CS 20082, 50130, Cherbourg-Octeville, France

^* e-mail: d.bonn@uva.nl

Received: 17 March 2018
Accepted: 9 November 2018
Published online: 12 December 2018

Abstract

Recent theories of drag reduction in wall turbulence assumed that the presence of the polymer leads to an effective viscosity, which increases linearly with the distance from the wall. Such a linear viscosity profile reduces the Reynolds stress (i.e., the momentum flux to the wall), which leads to drag reduction. For the usual flexible polymers employed in drag reduction, the effective viscosity is however a strongly non-linear effect that is difficult to quantify. We therefore investigate the turbulent drag reduction characteristics of a stiff rod-like polymer for which any effective viscosity changes are only due to the orientation of the polymers. The results show that close to the walls the polymers orient and the viscosity is low, whereas in the bulk the polymers are randomly oriented and the effective viscosity is high. This indeed leads to a reduction of the Reynolds stress and hence to a drag reduction.