Decay of turbulence in a liquid metal duct flow with transverse magnetic field

TL;DR

This study uses direct numerical simulations to analyze how turbulence in a liquid metal duct flow decays under a transverse magnetic field, revealing complex behavior influenced by initial flow conditions and large-scale structures.

Contribution

It provides detailed insights into turbulence decay mechanisms in magnetohydrodynamic flows, highlighting the role of flow state and large-scale structures in the presence of magnetic fields.

Findings

Large-scale quasi-two-dimensional structures persist during decay.

Turbulence decay is highly dependent on initial flow conditions.

Statistical properties like energy decay and correlations are characterized.

Abstract

Decay of honeycomb-generated turbulence in a duct with a static transverse magnetic field is studied via direct numerical simulations. The simulations follow the revealing experimental study of Sukoriansky et al. (1986), in particular the paradoxical observation of high-amplitude velocity fluctuations, which exist in the downstream portion of the flow when the strong transverse magnetic field is imposed in the entire duct including the honeycomb exit, but not in other configurations. It is shown that the fluctuations are caused by the large-scale quasi-two-dimensional structures forming in the flow at the initial stages of the decay and surviving the magnetic suppression. Statistical turbulence properties, such as the energy decay curves, two-point correlations and typical length scales are computed. The study demonstrates that turbulence decay in the presence of a magnetic field is a complex phenomenon critically depending on the state of the flow at the moment the field is introduced.