MHD turbulence in a channel with spanwise magnetic field

TL;DR

This study investigates how a spanwise magnetic field influences turbulent channel flow at low magnetic Reynolds number, revealing turbulence suppression, drag reduction, and flow profile changes through DNS and LES simulations.

Contribution

It provides new insights into the effects of spanwise magnetic fields on turbulence, validated by DNS and LES, with the dynamic Smagorinsky model accurately capturing flow transformations.

Findings

Turbulent velocity fluctuations are suppressed by the magnetic field.

Drag is reduced and the mean flow profile is altered.

The dynamic Smagorinsky model accurately reproduces flow changes.

Abstract

The effect of a uniform spanwise magnetic field on a turbulent channel flow is investigated for the case of low magnetic Reynolds number. DNS and LES computations are performed for two values of the hydrodynamic Reynolds number (10^4 and 2\times 10^4) and the Hartmann number varying in a wide range. It is shown that the main effect of the magnetic field is the suppression of turbulent velocity fluctuations and momentum transfer in the wall-normal direction. This leads to drag reduction and transformation of the mean flow profile. The centerline velocity grows, the mean velocity gradients near the wall decrease, and the typical horizontal dimensions of the coherent structures enlarge upon increasing the Hartmann number. Comparison between LES and DNS results shows that the dynamic Smagorinsky model accurately reproduces the flow transformation.