On the nature of laminar-turbulence intermittency in shear flows

TL;DR

This paper investigates the origin of spatial intermittency in shear flows, showing it results from local interactions between turbulent regions and persists at high Reynolds numbers, with implications for understanding turbulence transition.

Contribution

It introduces a model based on nearest neighbor interactions to explain the spatial intermittency in shear flows, supported by direct numerical simulations.

Findings

Intermittency arises from local interactions between turbulent regions.

Turbulent flows have a well-defined equilibrium turbulent fraction.

Laminar intermissions persist at arbitrarily high Reynolds numbers.

Abstract

In pipe, channel and boundary layer flows turbulence first occurs intermittently in space and time: at moderate Reynolds numbers domains of disordered turbulent motion are separated by quiescent laminar regions. Based on direct numerical simulations of pipe flow we here argue that the spatial intermittency has its origin in a nearest neighbor interaction between turbulent regions. We further show that in this regime turbulent flows are intrinsically intermittent with a well defined equilibrium turbulent fraction but without ever assuming a steady pattern. This transition scenario is analogous to that found in simple models such as coupled map lattices. The scaling observed implies that laminar intermissions of the turbulent flow will persist to arbitrarily large Reynolds numbers.