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Séminaire J. Zhang

28 octobre 2016

The dynamic behaviors of freely rising bubble(s) with/without external magnetic field

Séminaire Jie Zhang

Vendredi 4 novembre à 14h00

Salle Castex Rez de chaussée

Abstract :

In the experimental Tokamak fusion reactor, magnetic fields are used for plasma confinement, as a consequence, the liquid metal flows in the device are under the influence of MHD effect. In the blanket part of the fusion reactor, bubbles are always injected into the liquid metal to resist the MHD retarding effect, in order to increase perturbations in the flow to enhance heat transfer.
Therefore, in the present study, we aim to investigate the influence of the external magnetic field on the bubbly flows. To achieve this goal, we first studied the single bubble motion under MHD effect, after that, two bubbles rising side by side were further studied. Although it seems to be a very simple phenomena as we think, however, we obtain very interesting results. The variations of the bubble shapes, the rising paths, the rising velocities are presented under magnetic fields with different intensities and different directions, what is more important, the evolution of the vortex structures are analyzed in detail, proving that it is rather the decisive factor for path instability. By studying the dynamic behaviors of the bubble pairs under magnetic fields, we also found it is rather the vortex structures but not the collision velocity to determine whether two bubbles will coalesce or bounce after approaching. Also, by changing the direction of the magnetic fields, some different but interesting phenomena are observed, which helps us to understand the hydraulic bubble dynamics.