DYNAMO ACTION IN PRECESSING CYLINDERS
Résumé
It is numerically demonstrated by means of a magnetohydrodynamic (MHD) code that precession can trigger the dynamo action in a cylindrical container. When the angle between the spin axis and the precession axis is fixed to pi/2, two spinning ways can be explored: either the symmetry axis of the cylinder is parallel to the spin axis (denoted as the axial spin case) or it is perpendicular to the spin axis (denoted as the equatorial spin case). In both cases, when the Reynolds number, based on the radius of the cylinder and its spin angular velocity, increases, the flow, which is initially centro-symmetric, loses its stability and bifurcates to a quasi-periodic motion. This unsteady and asymmetric flow is shown to be capable of sustaining dynamo action in the linear and nonlinear regimes. The magnetic field thus generated is mainly quadrupolar in the axial spin case while it is mainly dipolar in the equatorial spin case. These numerical evidences of dynamo action in a precessing cylindrical container may be useful for the design of new dynamo experiments, such as the one planned at the DRESDYN facility in Germany [1].
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