Irreversible energy extraction from negative temperature two-dimensional turbulence

TL;DR

This paper investigates how negative temperature states in two-dimensional turbulence lead to irreversible energy transfer from microscopic fluctuations to macroscopic flow, using a theoretical model and numerical experiments.

Contribution

It introduces a conceptual model demonstrating irreversible energy extraction in negative temperature 2D turbulence and establishes a Jarzynski equality for energy exchange during domain shape changes.

Findings

Energy flows from microscopic to macroscopic in negative temperature states.

The Jarzynski equality relates energy transfer direction to initial temperature.

Numerical results confirm the theoretical predictions.

Abstract

The formation and transition of patterns of two-dimensional turbulent flows observed in various geophysical systems are commonly explained in terms of statistical mechanics. Different from ordinary systems, for a two-dimensional flow, the absolute temperature defined for a statistical equilibrium can take negative values. In a state of negative temperature, the second law of thermodynamics predicts that energy in microscopic fluctuations is irreversibly converted to a macroscopic form. This study explores the possibility of this one-way energy conversion in a two-dimensional flow using a basic conceptual model. We consider an inviscid incompressible fluid contained in a bounded domain, the shape of which is distorted by an externally imposed force. Unlike the usual fixed boundary cases, the flow energy within the domain is exchanged with the external system via pressure work through the moving lateral boundary. Concurrently, the flow field remains constrained by vorticity conservation. Beginning from a state of Kraichnan's grand-canonical ensemble, when the domain shape is distorted from one shape to another in a finite time, the Jarzynski equality is established. This equality states that, on average, the direction of a net energy flow through the boundary during a cycle of domain distortion changes with the sign of the initial temperature of the system. Numerical experiments are carried out to verify this theoretical argument and to investigate the parameter dependence of the energy exchange rate.