Comment on 'Critical behaviour in the relaminarization of localized turbulence in pipe flow'

TL;DR

This paper critically examines Willis and Kerswell's analysis of turbulent lifetime data in pipe flow, arguing that their conclusion of divergence near Re≈1870 is not definitive and could also be explained by exponential growth.

Contribution

It provides a re-analysis of previous numerical data, challenging the original claim of critical divergence in turbulent lifetimes in pipe flow.

Findings

Data is compatible with exponential lifetime increase

Original divergence conclusion is not conclusively supported

Re-analysis questions the critical Reynolds number estimate

Abstract

This is a comment on arXiv:physics/0608292, subsequently published in Phys Rev Lett, 98, 014501 (2007), in which Willis and Kerswell study in direct numerical simulations the statistics of turbulent lifetimes in pipe flow. They suggest that their data for six different Reynolds numbers support a divergence of the lifetime near a Reynolds number of about 1870. However, their conclusion is not compelling: a re-analysis of their data shows that it is also compatible with an exponentially increasing lifetime.