The Elsasser number, Λ, is a dimensionless number in
magnetohydrodynamics
In physics and engineering, magnetohydrodynamics (MHD; also called magneto-fluid dynamics or hydromagnetics) is a model of electrically conducting fluids that treats all interpenetrating particle species together as a single Continuum ...
that represents the ratio of magnetic forces to the Coriolis force.
where σ is the
conductivity of the fluid, ''B'' is the
magnetic field
A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...
, ρ is the density of the fluid, and Ω is the rate of rotation of the body.
Applications
This number is useful when studying the
linear stability
In mathematics, in the theory of differential equations and dynamical systems, a particular stationary or quasistationary solution to a nonlinear system is called linearly unstable if the linearization of the equation at this solution has the for ...
of an accretion disc to the
magnetorotational instability.
Notes
References
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{{Fluiddynamics-stub
Dimensionless numbers of fluid mechanics