Dynamical landscape of transitional pipe flow

TL;DR

This paper explores the complex transition from laminar to turbulent flow in pipes, identifying localized states like puffs and antipuffs within a unified bifurcation framework using the Barkley model.

Contribution

It introduces the concepts of antipuffs and gap-edge states, extending the understanding of localized states in pipe flow transition within a unified bifurcation picture.

Findings

Identification of antipuffs and gap-edge states.

Unified bifurcation framework for localized states.

Natural explanation of laminar gaps as antipuffs.

Abstract

The transition to turbulence in pipes is characterized by a coexistence of laminar and turbulent states. At the lower end of the transition, localized turbulent pulses, called puffs, can be excited. Puffs can decay when rare fluctuations drive them close to an edge state lying at the phase-space boundary with laminar flow. At higher Reynolds numbers, homogeneous turbulence can be sustained, and dominates over laminar flow. Here we complete this landscape of localized states, placing it within a unified bifurcation picture. We demonstrate our claims within the Barkley model, and motivate them generally. Specifically, we suggest the existence of an antipuff and a gap-edge -- states which mirror the puff and related edge state. Previously observed laminar gaps forming within homogeneous turbulence are then naturally identified as antipuffs nucleating and decaying through the gap edge.