Turbulent drag reduction: A universal perspective from energy fluxes

Abstract

Injection of dilute polymer in a turbulent flow suppresses frictional drag. This challenging and technologically important problem remains primarily unresolved due to the complex nature of the flow. An important factor in the drag reduction is the energy transfer from the velocity field to the polymers. In this paper we quantify this process using energy fluxes, as well as show its universality in diverse flows such as magnetohydrodynamics, quasi-static magnetohydrodynamics, and bubbly turbulence. We show that in such flows, the transfer from kinetic energy to elastic energy leads to a reduction in kinetic energy flux compared to the corresponding hydrodynamic turbulence. This leads to a reduction in nonlinearity of the velocity field that results into a more ordered flow and a suppression of turbulent drag.