Travelling waves in a cylindrical magnetohydrodynamically forced flow
Résumé
We present an experimental study of a liquid metal flow electromagnetically forced
in a large aspect ratio coaxial cylindrical geometry. An azimuthal Lorentz force is
applied on the liquid metal gap, through a radial current and an axial magnetic field.
Using ultrasonic velocity measurements, we focus on the effect of these two parameters
on the flow properties. We show that, depending on the strength of the magnetic
field and not only on the applied Lorentz force, different dynamical states exist. We
first observe a stationary structure at low forcing. Then, two other regimes of different
travelling waves are exhibited at higher forcing. We characterize them by their
different frequencies and speeds. Higher magnetic fields clearly promote the faster
waves. Connections with other magnetohydrodynamics instabilities are discussed.
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