Direct Assessment of Vorticity Alignment with Local and Nonlocal Strain Rates in Turbulent Flows

TL;DR

This paper uses a Biot-Savart integration to decompose strain rates in turbulence, revealing that vorticity aligns with the nonlocal strain's extensional eigenvector, highlighting the role of nonlocal effects in vortex stretching.

Contribution

It introduces a novel decomposition of strain rate into local and nonlocal parts and demonstrates the vorticity's alignment with the nonlocal strain's extensional eigenvector.

Findings

Vorticity aligns with the intermediate eigenvector of the total strain rate.

Vorticity aligns with the most extensional eigenvector of the nonlocal strain rate.

Nonlocal strain significantly influences vortex stretching dynamics.

Abstract

A direct Biot-Savart integration is used to decompose the strain rate into its local and nonlocal constituents, allowing the vorticity alignment with the local and nonlocal strain rate eigenvectors to be investigated. These strain rate tensor constituents are evaluated in a turbulent flow using data from highly-resolved direct numerical simulations. While the vorticity aligns preferentially with the intermediate eigenvector of the \textit{combined} strain rate, as has been observed previously, the present results for the first time clearly show that the vorticity aligns with the most extensional eigenvector of the \textit{nonlocal} strain rate. This in turn reveals a significant linear contribution to the vortex stretching dynamics in turbulent flows.