Dynamics and evolution of Turbulent Taylor rolls

TL;DR

This paper investigates the structure, origin, and dynamics of Taylor rolls in turbulent Taylor-Couette flow, revealing their relation to shear and anti-cyclonic rotation rather than centrifugal instability, and analyzing their dependence on domain size.

Contribution

It clarifies the nature of Taylor rolls at high Reynolds numbers, showing they are linked to shear and rotation effects and are not solely due to centrifugal instability.

Findings

Taylor rolls are diverse in vorticity distribution and driving mechanisms.

Rolls are maintained by shear and anti-cyclonic rotation, not centrifugal instability.

The position of the rolls is governed by a stochastic process influenced by domain size.

Abstract

In many shear- and pressure-driven wall-bounded turbulent flows secondary motions spontaneously develop and their interaction with the main flow alters the overall large-scale features and transfer properties. Taylor-Couette flow, the fluid motion developing in the gap between two concentric cylinders rotating at different angular velocity, is not an exception, and toroidal Taylor rolls have been observed from the early development of the flow up to the fully turbulent regime. In this manuscript we show that under the generic name of ``Taylor rolls'' there is a wide variety of structures that differ for the vorticity distribution within the cores, the way they are driven and their effects on the mean flow. We relate the rolls at high Reynolds numbers not to centrifugal instabilities, but to a combination of shear and anti-cyclonic rotation, showing that they are preserved in the limit of vanishing curvature and can be better understood as a pinned cycle which shows similar characteristics as the self-sustained process of shear flows. By analyzing the effect of the computational domain size, we show that this pinning is not a product of numerics, and that the position of the rolls is governed by a random process with the space and time variations depending on domain size.