Magnetic Dissipation of Near-Wall Turbulent Coherent Structures in Magnetohydrodynamic Pipe Flows

TL;DR

This paper investigates how magnetic fields influence turbulent pipe flows, proposing that the ratio of Hartmann number to friction Reynolds number predicts flow relaminarization, supported by experimental data.

Contribution

It introduces the ratio M/R_τ as a key parameter for predicting laminar-turbulent transition in magnetohydrodynamic pipe flows.

Findings

M/R_τ effectively predicts relaminarization.

Experimental data supports the proposed parameter.

Relaminarization depends on magnetic and flow parameters.

Abstract

Relaminarization of wall-bounded turbulent flows by means of external static magnetic fields is a long-known phenomenon in the physics of electrically conducting fluids at low magnetic Reynolds numbers. Despite the large literature on the subject, it is not yet completely clear what combination of the Hartmann ($M$) and the Reynolds number has to be used to predict the laminar-turbulent transition in channel or pipe flows fed by upstream turbulent flows free of magnetic perturbations. Relying upon standard phenomenological approaches related to mixing length and structural concepts, we put forward that $M/R_\tau$, where $R_\tau$ is the friction Reynolds number, is the appropriate controlling parameter for relaminarization, a proposal which finds good support from available experimental data.