Active and hibernating turbulence in minimal channel flow of Newtonian and polymeric fluids

TL;DR

This study simulates turbulent channel flow of Newtonian and polymeric fluids in minimal geometries, revealing hibernating turbulence intervals that resemble the maximum drag reduction state, with increased viscoelasticity leading to more frequent MDR-like flows.

Contribution

It uncovers the existence of hibernating turbulence intervals in minimal channel flows and links viscoelasticity to increased MDR-like behavior, advancing understanding of drag reduction mechanisms.

Findings

Hibernating turbulence features resemble the MDR asymptote.

Frequency of hibernating intervals increases with viscoelasticity.

Flow characteristics match experimental observations of drag reduction.

Abstract

Turbulent channel flow of drag-reducing polymer solutions is simulated in minimal flow geometries. Even in the Newtonian limit, we find intervals of "hibernating" turbulence that display many features of the universal maximum drag reduction (MDR) asymptote observed in polymer solutions: weak streamwise vortices, nearly nonexistent streamwise variations and a mean velocity gradient that quantitatively matches experiments. As viscoelasticity increases, the frequency of these intervals also increases, while the intervals themselves are unchanged, leading to flows that increasingly resemble MDR.