Reynolds number (for a magnetic field)

Description

The magnetic Reynolds number is the magnetic analogue of the Reynolds number, a fundamental dimensionless group that occurs in magnetohydrodynamics. It gives an estimate of the relative effects of advection or induction of a magnetic field by the motion of a conducting medium, often a fluid, to magnetic diffusion.

The mechanism by which the motion of a conducting fluid generates a magnetic field is the subject of dynamo theory. When the magnetic Reynolds number is very large, however, diffusion and the dynamo are less of a concern, and in this case focus instead often rests on the influence of the magnetic field on the flow.

Related formulas

Variables

Rmmagnetic Reynolds number (dimensionless) (dimensionless)
Utypical velocity scale of the flow (m/s)
Lypical length scale of the flow (m)
ηmagnetic diffusivity (m2/s)