Helical rotating turbulence. Part II. Intermittency, scale invariance and structures

TL;DR

This study investigates the intermittency and scale invariance in helical rotating turbulence, revealing that energy cascades are scale-invariant while helicity cascades are highly intermittent, with complex structures at small scales.

Contribution

It provides detailed analysis of intermittency and scale invariance in helical rotating turbulence using high-resolution simulations, highlighting differences between energy and helicity cascades.

Findings

Energy cascade is scale invariant and non-intermittent.

Helicity cascade is highly intermittent.

Small-scale flow exhibits recovery of isotropy.

Abstract

We study the intermittency properties of the energy and helicity cascades in two 1536^3 direct numerical simulations of helical rotating turbulence. Symmetric and anti-symmetric velocity increments are examined, as well as probability density functions of the velocity field and of the helicity density. It is found that the direct cascade of energy to small scales is scale invariant and non-intermittent, whereas the direct cascade of helicity is highly intermittent. Furthermore, the study of structure functions of different orders allows us to identify a recovery of isotropy of strong events at very small scales in the flow. Finally, we observe the juxtaposition in space of strong laminar and persistent helical columns next to time-varying vortex tangles, the former being associated with the self-similarity of energy and the latter with the intermittency of helicity.