Direct transition to elastoinertial turbulence from a linear instability in channel flow

TL;DR

This paper demonstrates a novel linear instability in viscoelastic channel flow that directly causes transition to elastoinertial turbulence, challenging the previous belief that nonlinear instabilities were necessary.

Contribution

It provides numerical evidence for a new linear instability mechanism that directly triggers elastoinertial turbulence in channel flow.

Findings

Identifies a 2D linear instability leading to turbulence

Shows larger disturbances cause transition to nonlinear turbulent states

Highlights the importance of nonlinear effects in turbulence development

Abstract

For decades, transition to turbulence in viscoelastic parallel shear flows was believed to require nonlinear instabilities. We provide numerical evidences for a new wall-mode linear instability that directly triggers the transition to elastoinertial turbulence in channel flow. The instability is 2D but 3D features become important as nonlinear effects grow. With larger disturbances, direct transition to nonlinear instabilities, leading to turbulent states of both inertial and elastoinertial natures, are observed.