RESUMEN
We use a combination of numerical simulations and experiments to elucidate the structure of the flow of an electrically conducting fluid past a localized magnetic field, called magnetic obstacle. We demonstrate that the stationary flow pattern is considerably more complex than in the wake behind an ordinary body. The steady flow is shown to undergo two bifurcations (rather than one) and to involve up to six (rather than just two) vortices. We find that the first bifurcation leads to the formation of a pair of vortices within the region of magnetic field that we call inner magnetic vortices, whereas a second bifurcation gives rise to a pair of attached vortices that are linked to the inner vortices by connecting vortices.
RESUMEN
We investigate the influence of thermoelectric effect on the onset of thermal instability in the Rayleigh-Bénard system with vertical magnetic field. An electrically conducting fluid is confined in an infinite horizontal layer between thick thermally and electrically conducting walls. A horizontal temperature variation resulting from convective instability leads to horizontal temperature gradients along the liquid-solid interface acting as a source of thermoelectric currents. Through interaction with the applied magnetic field, the Lorentz force is created modifying the instability. We find that the critical Rayleigh number for onset of convection is not changed by the thermoelectric effect. However, the thermal gradient on the liquid-solid boundary leads to a change of the shape of the unstable mode creating helical flow in the evolving convection rolls because of the Lorentz force parallel to their axis. The created kinetic helicity depends linearly on the dimensionless parameter K(TE) characterizing the strength of the thermoelectric effect.
