Hindered energy cascade in highly helical isotropic turbulence

TL;DR

This paper introduces a new phenomenology for isotropic turbulence that accounts for helicity, showing that helicity can hinder energy transfer and cause a bottleneck effect, confirmed by high Reynolds number simulations.

Contribution

It presents the first generalized phenomenology for helical turbulence, revealing how helicity impacts the energy cascade and causes spectral energy accumulation.

Findings

Helicity can hinder the spectral energy transfer in turbulence.

A helical bottleneck effect appears in the inertial range.

Numerical simulations confirm the proposed phenomenology.

Abstract

The conventional approach to the turbulent energy cascade, based on Richardson-Kolmogorov phenomenology, ignores the topology of emerging vortices, which is related to the helicity of the turbulent flow. It is generally believed that helicity can play a significant role in turbulent systems, e.g., supporting the generation of large-scale magnetic fields, but its impact on the energy cascade to small scales has never been observed. We suggest for the first time a generalized phenomenology for isotropic turbulence with an arbitrary spectral distribution of the helicity. We discuss various scenarios of direct turbulent cascades with new helicity effect, which can be interpreted as a hindering of the spectral energy transfer. Therefore the energy is accumulated and redistributed so that the efficiency of non-linear interactions will be sufficient to provide a constant energy flux. We confirm our phenomenology by high Reynolds number numerical simulations based on a shell model of helical turbulence. The energy in our model is injected at a certain large scale only, whereas the source of helicity is distributed over all scales. In particular, we found that the helical bottleneck effect can appear in the inertial interval of the energy spectrum.