The non-equilibrium region of grid-generated decaying turbulence

TL;DR

This paper investigates the non-equilibrium dissipation law in grid-generated decaying turbulence across various flow configurations, revealing its robustness despite differences in flow inhomogeneity and anisotropy.

Contribution

It demonstrates that the non-equilibrium dissipation law applies broadly to different turbulent flows, even when traditional equilibrium laws are also observed.

Findings

The non-equilibrium dissipation law is consistent across different turbulence types.

The law is not dependent on the choice of integral scale.

Both equilibrium and non-equilibrium laws can coexist in the same flow.

Abstract

The previously reported non-equilibrium dissipation law is investigated in turbulent flows generated by various regular and fractal square grids. The flows are documented in terms of various turbulent profiles which reveal their differences. In spite of significant inhomogeneity and anisotropy differences, the new non-equilibrium dissipation law is observed in all these flows. Various transverse and longitudinal integral scales are measured and used to define the dissipation coefficient $C_{\varepsilon}$. It is found that the new non-equilibrium dissipation law is not an artefact of a particular choice of the integral scale and that the usual equilibrium dissipation law can actually coexist with the non-equilibrium law in different regions of the same flow.