Nonlinear cascades in two-dimensional turbulent magnetoconvection

TL;DR

This paper investigates the spectral transport dynamics in two-dimensional turbulent magnetoconvection using DNS, revealing quasi-oscillations between MHD-dominated and buoyancy-dominated turbulence regimes driven by cross-helicity.

Contribution

It reports the first observation of self-excited transitions between turbulence regimes in 2D MHD convection, controlled by cross-helicity and explained through spectral energy transfer mechanisms.

Findings

Identification of quasi-oscillations between turbulence regimes

Role of cross-helicity in regime transitions

Spectral transfer processes in MHD turbulence

Abstract

The dynamics of spectral transport in two-dimensional turbulent convection of electrically conducting fluids is studied by means of direct numerical simulations (DNS) in the frame of the magnetohydrodynamic (MHD) Boussinesq approximation. The system performs quasi-oscillations between two different regimes of small-scale turbulence: one dominated by nonlinear MHD interactions, the other governed by buoyancy forces. The self-excited change of turbulent states is reported here for the first time. The process is controlled by the ideal invariant cross-helicity, $H^\mathrm{C}=\int_S \mathrm{d}S \mathbf{v}\cdot\mathbf{b}$. The observations are explained by the interplay of convective driving with the nonlinear spectral transfer of total MHD energy and cross-helicity.