Power Fluctuations and Irreversibility in Turbulence

TL;DR

This paper investigates the breaking of detailed balance in turbulence, revealing that fluid elements decelerate faster than they accelerate and highlighting fundamental differences in energy exchange between two and three-dimensional flows.

Contribution

It provides new insights into irreversibility and energy transfer mechanisms in turbulence by analyzing kinetic energy evolution and detailed balance breaking.

Findings

Fluid elements decelerate faster than they accelerate.

Negative third moments of energy increments observed across flows.

Distinct energy transfer patterns in 2D and 3D turbulence.

Abstract

The breaking of detailed balance, the symmetry between forward and backward probability transition between two states, is crucial to understand irreversible systems. In hydrodynamic turbulence, a far-from equilibrium system, we observe a strong manifestation of the breaking of detailed balance by following the evolution of the kinetic energy of individual fluid elements. We found in all the flows that we have investigated that fluid elements decelerate faster than they accelerate, giving rise to negative third moment of energy increments, independently of space dimensionality. The exchange of energy between fluid elements however is fundamentally different in two and three dimensions. While pressure forces do not provide net energy change to slow or fast particles in two dimensions, they tend to transfer energy from {\it slow} to {\it fast} particles in three dimensions, possibly implying a runaway of energy.