title: Shell model for drag reduction with polymer additives in homogeneous turbulence.
abstract: Recent direct numerical simulations of the finite-extensibility nonlinear elastic dumbbell model with the Peterlin approximation of non-Newtonian hydrodynamics revealed that the phenomenon of drag reduction by polymer additives exists (albeit in reduced form) also in homogeneous turbulence. We use here a simple shell model for homogeneous viscoelastic flows, which recaptures the essential observations of the full simulations. The simplicity of the shell model allows us to offer a transparent explanation of the main observations. It is shown that the mechanism for drag reduction operates mainly on large scales. Understanding the mechanism allows us to predict how the amount of drag reduction depends on the various parameters in the model. The main conclusion is that drag reduction is not a universal phenomenon; it peaks in a window of parameters such as the Reynolds number and the relaxation rate of the polymer.
authors.affiliation: Dipartimento di Fisica and INFM, Università Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Roma, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Benzi
authors.forename: Elisabetta
authors.initials: E
authors.lastname: De Angelis
authors.forename: Rama
authors.initials: R
authors.lastname: Govindarajan
authors.forename: Itamar
authors.initials: I
authors.lastname: Procaccia