Numerical analysis of MHD effects resulting from spatial variations of high magnetic fields applied to a rectangular duct flow
Résumé
A fully three dimensional numerical analysis is performed in order to study turbulent flow of liquid metals in rectangular ducts under the influence of high magnetic fields. The goal of this analysis is to improve the level of understanding MHD effects in liquid metal cooled fusion reactor. The turbulent flow is computed in the case of uniform and non-uniform high magnetic fields. The flow computations for a duct in a non-uniform magnetic field, show M-shaped velocity profiles in the upstream region of the longitudinal plane of the flow, and respectively low intensity wall jets in the downstream region. This flow pattern is explained by the induced electrical currents which are closed in both the longitudinal and transversal planes, generating Lorentz forces acting parallel and, respectively, perpendicular to the flow. When the applied magnetic field is uniform, the velocity distribution is slightly affected by the Lorentz forces. The results show flattened velocity profiles in the core region, and no jet flow emerging near the walls. This result is explained by the closure path of eddy currents only in the transversal plane of the flow. By introducing some variation of the axial magnetic field in the computation, no significant changes are observed in the velocity profiles. The velocity profiles are significantly affected by the axial gradient of the magnetic field, only at the entrance and, respectively, at the exit of the rectangular duct from a uniform magnetic field. The flow damping in the core region is much stronger at the entry and, respectively, at the exit side from an extended zone with uniform magnetic field, as compared to the case of a liquid metal flowing through a narrow magnetic system.
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