The effects of a constant magnetic field on electrically
conducting liquid-metal flows
in a parallelepiped cavity are investigated using a spectral numerical
method involving direct numerical solution of the Navier–Stokes and
Ohm equations for three-dimensional flows. Three horizontal Bridgman
configurations are studied: buoyancy-driven convection in a confined cavity
and in a cavity where the top boundary is
a stress-free surface and thirdly, thermocapillary-driven flow in a cavity
where the
upper boundary is subjected to effects of surface tension. The results
of varying the Hartmann number (Ha) are described for a cavity
with Ax = L/H = 4 and
Ay = W/H = 1, where L is the length,
W is the width and H is the height of the
cavity. In general, an increase in the strength of the applied magnetic
field leads to
several fundamental changes in the properties of thermal convection. The
convective circulation progressively loses its intensity and when
Ha reaches a certain critical
value, which is found to depend on the direction (longitudinal or vertical)
of
the
applied magnetic field, decrease of the flow intensity takes on an
asymptotic form with important changes in the structure of the flow
circulation. The flow structure may be separated into three regions:
the core flow, Hartmann layers which develop in the
immediate vicinity of the rigid horizontal boundaries or at the
endwalls, and parallel
layers appearing in the vicinity of the sidewalls. The behaviour of
the maxima of velocity and of the overall flow circulation is found
to depend on both the boundary conditions used and the direction of
the applied magnetic field. Furthermore, the interaction of the
electric current density with the applied magnetic field
which leads to the structural reorganization described above can
also create more subtle flow modifications, such as flow inversions
which are observed mainly in the central region of the cavity.
Generation of Reverse Meniscus Flow by Applying An Electromagnetic Brake