Dipoles and streams in two-dimensional turbulence

TL;DR

This paper reveals that in two-dimensional turbulence, elongated streams formed by dipoles carry most of the kinetic energy, with vortices separating into fast-moving cores and a slow, crystalline family that dominates energy dynamics.

Contribution

It demonstrates the crucial role of dipoles and streams in the energy distribution and vortex organization in 2D turbulence, highlighting the importance of the slow, crystalline vortex family.

Findings

Streams formed by dipoles carry most kinetic energy.

Vortices separate into fast cores and slow, crystalline families.

The slow vortex family is responsible for the flow's energy dynamics.

Abstract

Following the suggestion from the Monte--Carlo experiments in Jim\'enez, J. of Turbul. 2020), that dipoles are as important to the dynamics of decaying two-dimensional turbulence as individual vortex cores, it is found that the kinetic energy of this flow is carried by elongated streams formed by the concatenation of dipoles. Vortices separate into a family of small fast-moving cores, and another family of larger slowly moving ones, which can be described as `frozen' into a slowly evolving `crystal'. The kinematics of both families are very different, and only the former is self-similar. The latter is responsible for most of the kinetic energy of the flow, and its vortices form the dipoles and the streams. Mechanisms are discussed for the growth of this slow component.