The role of polymer parameters and configurations in drag-reduced turbulent wall-bounded flows: Comparison between FENE and FENE-P

Abstract

Polymer-laden turbulent pipe flows are investigated through direct numerical simulations with Lagrangian transport, and back reaction, of 108 polymers, modelled as FENE dumbbells. A wide range Weissenberg number (Wi) comparison with results obtained via the FENE-P model shows quantitative and qualitative discrepancies between the two models. It is shown that the relevant hypothesis that fails and causes the differences is Peterlin’s approximation, leading to unphysical polymer extensions and thus back reaction. A new parameter, the polymer Reynolds number Rep is defined. At fixed Rep and Re, the dynamics depends only on Wi and not on the individual polymer parameters, i.e. friction coefficient γ, contour length L, and concentration co, entering in Rep. Alongside the increase in available computational power, this finding allows reducing drastically the cost of Lagrangian simulations, since co, γ, and L can be interchanged, and propose the FENE model as a valuable alternative to the well-established, and meritorious, FENE-P model.