On the decay of turbulence in plane Couette flow (long version)

TL;DR

This paper investigates how turbulent bands in plane Couette flow decay as the Reynolds number decreases, revealing a two-stage process involving rupture and shrinking, with implications for understanding turbulence decay.

Contribution

It provides a detailed analysis of the fragmentation and decay mechanisms of turbulent bands in large systems, using long-duration direct numerical simulations.

Findings

Decay involves rupture and slow shrinking of bands

Turbulence persists down to a global stability threshold

Discussion of decay within chaos and intermittency frameworks

Abstract

Upon decreasing the Reynolds number, plane Couette flow first forms alternately turbulent and laminar oblique bands out of featureless turbulence below some upper threshold R_t. These bands exist down to a global stability threshold R_g below which laminar flow ultimately prevails. We study the fragmentation and decay of these bands in systems that are extended enough for several bands to exist. We use direct numerical simulations appropriately tailored to deal with such large systems during long enough durations. We point out a two-stage process involving the rupture of a band and next its slow shrinking. Previous interpretations of turbulence decay in wall-bounded flows within the chaotic transient or spatiotemporal intermittency paradigms are discussed.