Kinetic helicity decay in linearly forced turbulence

TL;DR

This study investigates how kinetic helicity decays in forced turbulence through numerical models, revealing that helicity diminishes on a turbulent time scale regardless of forcing type or Reynolds number.

Contribution

It compares helicity decay in turbulence driven by external forcing versus linear forcing, showing decay occurs on a turbulent time scale in both cases.

Findings

Kinetic helicity decays regardless of forcing type.

Decay occurs on a turbulent time scale.

Helicity decay is independent of Reynolds number.

Abstract

The decay of kinetic helicity is studied in numerical models of forced turbulence using either an externally imposed forcing function as an inhomogeneous term in the equations or, alternatively, a term linear in the velocity giving rise to a linear instability. The externally imposed forcing function injects energy at the largest scales, giving rise to a turbulent inertial range with nearly constant energy flux while for linearly forced turbulence the spectral energy is maximum near the dissipation wavenumber. Kinetic helicity is injected once a statistically steady state is reached, but it is found to decay on a turbulent time scale regardless of the nature of the forcing and the value of the Reynolds number.