Spatio-temporal intermittency of the turbulent energy cascade

TL;DR

This paper investigates the highly intermittent and correlated spatio-temporal fluctuations in turbulent energy transfer, emphasizing the role of sweeping, non-locality, and geometrical alignments in incompressible turbulence.

Contribution

It reveals the detailed spatio-temporal structure and correlations of energy transfer fluctuations, highlighting effects absent in average turbulence models.

Findings

Intense, intermittent fluctuations of energy transfer and related terms.

Correlations caused by sweeping, non-locality, and geometrical alignments.

These effects are not captured by traditional average-based turbulence descriptions.

Abstract

In incompressible and periodic statistically stationary turbulence, exchanges of turbulent energy across scales and space are characterised by very intense and intermittent spatio-temporal fluctuations around zero of the time-derivative term, the spatial turbulent transport of fluctuating energy, and the pressure-velocity term. These fluctuations are correlated with each other and with the intense intermittent fluctuations of the interscale energy transfer rate. These correlations are caused by the sweeping effect, the link between non-linearity and non-locality, and also relate to geometrical alignments between the two-point fluctuating pressure force difference and the two-point fluctuating velocity difference in the case of the correlation between the interscale transfer rate and the pressure-velocity term. All these processes are absent from the spatio-temporal average picture of the turbulence cascade in statistically stationary and homogeneous turbulence.