We investigate experimentally the up- and downstream flow around an insulating cylinder in a conducting fluid subjected to an aligned magnetic field for low values of the magnetic Reynolds number Rm. For high values of the Alfvén number α = B0/U0(ρμ0)½ the upstream flow is characterized by magnetic and kinematic wakes. In this configuration we have measured, for the first time, the local values of the induced magnetic field. The results were analysed in a confined situation and show that the Oseen number k = ½Rm(1-α2) is the main parameter that characterizes the perturbation. In the downstream flow the two fields of perturbations (magnetic and kinetic) are characterized by von Kármán eddies. Our experiments were focused on the evolution of these eddies and show in particular that the critical Reynolds number increases strongly with the intensity of the magnetic field.
Pressure distribution measurements around a cylinder placed in a liquid metal flow aligned with a constant magnetic field are presented. The pressure drag is derived from these measurements and is found to be reduced by the electromagnetic forces for values of the interaction parameter. N, around unity. For higher values of N, the rear pressure and the global pressure drag exhibit a linear dependence with the square root of the interaction parameter and it is also shown that, for a sufficient value of the magnetic field, the von Karman street behind the cylinder is suppressed.
In order to understand the influence of crucible geometry combined with natural convection and Marangoni convection on melt flow pattern, temperature and pressure fields in silicon Czochralski crystal growth process, a set of numerical simulations was conducted. We carry out calculation enable us to determine temperature, pressure and velocity fields in function of Grashof and Marangoni numbers. The essential results show that the hemispherical geometry of crucible seems to be adapted for the growth of a good quality crystal and the pressure field is strongly affected by natural and Marangoni convection and it is more sensitive than temperature.
Most of the studies concerning the dynamo effect are motivated
by astrophysical and
geophysical applications. The dynamo effect is also the subject of some
experimental
studies in fast breeder reactors (FBR) for they contain liquid sodium in
motion with
magnetic Reynolds numbers larger than unity. In this paper, we are concerned
with
the flow of sodium inside the core of an FBR, characterized by a strong
helicity. The
sodium in the core flows through a network of vertical cylinders. In each
cylinder
assembly, the flow can be approximated by a smooth upwards helical motion
with
no-slip conditions at the boundary. As the core contains a large number
of assemblies,
the global flow is considered to be two-dimensionally periodic. We investigate
the
self-excitation of a two-dimensionally periodic magnetic field using an
instability
analysis of the induction equation which leads to an eigenvalue problem.
Advantage
is taken of the flow symmetries to reduce the size of the problem. The
growth
rate of the magnetic field is found as a function of the flow pitch, the
magnetic
Reynolds number (Rm) and the vertical magnetic wavenumber
(k). An α-effect is
shown to operate for moderate values of Rm, supporting a mean
magnetic field.
The large-Rm limit is investigated numerically.
It is found that α=O(Rm−2/3),
which can be explained through appropriate dynamo mechanisms. Either a
smooth
Ponomarenko or a Roberts type of dynamo is operating in each periodic cell,
depending on
k. The standard power regime of an industrial FPBR is found to
be subcritical.
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