Exact coherent structures and shadowing in turbulent Taylor-Couette flow

TL;DR

This paper explores the role of exact coherent structures (ECSs) in turbulent Taylor-Couette flow, providing numerical evidence that turbulent flows shadow ECSs, which supports the theoretical framework linking ECSs to turbulence.

Contribution

It presents the first direct numerical evidence of turbulent flow shadowing ECSs in a realistic experimental setup with boundary conditions matching real-world experiments.

Findings

Turbulent flow shadows unstable relative periodic orbits.

Turbulent flow shadows a traveling wave.

Supports ECS framework for turbulence modeling.

Abstract

We investigate a theoretical framework for modeling fluid turbulence based on the formalism of exact coherent structures (ECSs). Although highly promising, existing evidence for the role of ECSs in turbulent flows is largely circumstantial and comes primarily from idealized numerical simulations. In particular, it remains unclear whether three-dimensional turbulent flows in experiment shadow any ECSs. In order to conclusively answer this question, a hierarchy of ECSs should be computed on a domain and with boundary conditions exactly matching experiment. The present study makes the first step in this direction by investigating a small-aspect-ratio Taylor-Couette flow with naturally periodic boundary condition in the azimuthal direction. We describe the structure of the chaotic set underlying turbulent flow driven by counter-rotating cylinders and present direct numerical evidence for shadowing of a collection of unstable relative periodic orbits and a traveling wave, setting the stage for further experimental tests of the framework.