Multiple states in highly turbulent Taylor-Couette flow

TL;DR

This study provides conclusive evidence of multiple turbulent states in highly turbulent Taylor-Couette flow at large Reynolds numbers, challenging the traditional view of a single universal turbulent state.

Contribution

It is the first to demonstrate multiple turbulent states at high Reynolds numbers in Taylor-Couette flow, indicating bifurcations in high-dimensional turbulence.

Findings

Multiple turbulent states observed at Re ~ 10^6

Global torque and local velocity measurements confirm multiple states

Challenges Kolmogorov's paradigm of a single turbulent state

Abstract

The ubiquity of turbulent flows in nature and technology makes it of utmost importance to fundamentally understand turbulence. Kolmogorov's 1941 paradigm suggests that for strongly turbulent flows with many degrees of freedom and its large fluctuations, there would only be \emph{one} turbulent state as the large fluctuations would explore the entire higher-dimensional phase space. Here we report the first conclusive evidence of multiple turbulent states for large Reynolds number $\text{Re}=\mathcal{O}(10^6)$ (Taylor number $\text{Ta}=\mathcal{O}(10^{12})$) Taylor-Couette flow in the regime of ultimate turbulence, by probing the phase space spanned by the rotation rates of the inner and outer cylinder. The manifestation of multiple turbulent states is exemplified by providing combined global torque and local velocity measurements. This result verifies the notion that bifurcations can occur in high-dimensional flows i.e. very large $\text{Re}$) and questions Kolmogorov's paradigm.