4 research outputs found
A numerical model of the VKS experiment
We present numerical simulations of the magnetic field generated by the flow
of liquid sodium driven by two counter-rotating impellers (VKS experiment).
Using a dynamo kinematic code in cylindrical geometry, it is shown that
different magnetic modes can be generated depending on the flow configuration.
While the time averaged axisymmetric mean flow generates an equatorial dipole,
our simulations show that an axial field of either dipolar or quadrupolar
symmetry can be generated by taking into account non-axisymmetric components of
the flow. Moreover, we show that by breaking a symmetry of the flow, the
magnetic field becomes oscillatory. This leads to reversals of the axial dipole
polarity, involving a competition with the quadrupolar component.Comment: 6 pages, 5 figure
Chaotic magnetic field reversals in turbulent dynamos
We present direct numerical simulations of reversals of the magnetic field
generated by swirling flows in a spherical domain. In agreement with a recent
model, we observe that coupling dipolar and quadrupolar magnetic modes by an
asymmetric forcing of the flow generates field reversals. In addition, we show
that this mechanism strongly depends on the value of the magnetic Prandtl
number.Comment: 4 pages, 5 figure
Effect of magnetic boundary conditions on the dynamo threshold of von Kármán swirling flows
We study the effect of different boundary conditions on the
kinematic dynamo threshold of von Kármán type swirling flows in a
cylindrical geometry. Using an analytical test flow, we model different
boundary conditions: insulating walls all over the flow, effect of sodium
at rest on the cylinder side boundary, effect of sodium behind the impellers, effect of impellers or side wall made of a
high-magnetic-permeability material. We find that using high-magnetic-permeability boundary conditions decreases the dynamo threshold, the
minimum being achieved when they are implemented all over the flow