A Lagrangian model for the evolution of turbulent magnetic and passive scalar fields

TL;DR

This paper extends the Recent Fluid Deformation closure to model the evolution of turbulent magnetic and passive scalar fields, comparing its predictions with direct numerical simulations.

Contribution

It introduces an extension of the RFD closure for modeling magnetic and scalar turbulence, highlighting differences in stretching effects.

Findings

RFD closure accurately predicts PDFs of magnetic fluctuations

RFD closure captures the reversed stretching effect for passive scalars

Comparison with DNS validates the model's effectiveness

Abstract

In this paper we present an extension of the \emph{Recent Fluid Deformation (RFD)} closure introduced by Chevillard and Meneveau (2006) which was developed for modeling the time evolution of Lagrangian fluctuations in incompressible Navier-Stokes turbulence. We apply the RFD closure to study the evolution of magnetic and passive scalar fluctuations. This comparison is especially interesting since the stretching term for the magnetic field and for the gradient of the passive scalar are similar but differ by a sign such that the effect of stretching and compression by the turbulent velocity field is reversed. Probability density functions (PDFs) of magnetic fluctuations and fluctuations of the gradient of the passive scalar obtained from the RFD closure are compared against PDFs obtained from direct numerical simulations.