Impact of boundary conditions on onset and symmetry of precession-driven dynamos
Year: 2026
Type: article
Abstract: We numerically examine a kinematic dynamo driven by precession in a cylindrical geometry, with particular emphasis on the narrow range of Poincaré numbers where dynamo action is most likely at low and moderate magnetic Reynolds numbers. Using time-averaged velocity fields obtained from hydrodynamic simulations, we analyze the symmetry, oscillation frequency, and onset of the leading magnetic eigenmodes. Two competing families of magnetic fields are identified: a centro-symmetric, higher-frequency quadrupolar mode and a centroantisymmetric, lower-frequency dipolar mode. We then quantify how the dynamo threshold depends on the electromagnetic boundary conditions, including pseudo-vacuum versus true vacuum treatment and the presence of conducting and/or magnetically permeable vessel walls. We show that simplified vanishing-tangential-field boundary conditions systematically underestimate the critical magnetic Reynolds number, whereas realistic outer layers can either promote or suppress dynamo action depending on their electrical conductivity and on the selected hydrodynamic mean state. These results clarify the role of wall properties and mode selection for the forthcoming DRESDYN precession dynamo experiment.
Source: Physical Review Fluids
DOI: 10.1103/rx1h-5zxp
Language: English
Subfield: Geophysics
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7169803348