A parametric study of precession driven dynamos inside a sphere.

This article investigates the dynamo action driven by precession in an electrically conducting fluid contained within a precessing sphere, using direct numerical simulations based on a Galerkin spectral method with helical wave decomposition. The study explores the effects of varying nutation angles (30°, 60°, 90°), precession ratios (Poincaré number), Reynolds number, and magnetic Prandtl number on the feasibility and characteristics of self-sustained dynamos. It finds that a nutation angle of 90° is most effective for dynamo action, followed by 60° with retrograde precession, and that moderate precession ratios around ±0.3 optimize dynamo onset. The generated magnetic fields are not predominantly dipolar, contrasting with convection-driven dynamos, and exhibit diverse temporal behaviors including steady, periodic, quasi-periodic, turbulent states, and magnetic dipole reversals with varying timescales. The study notes that the parameter regimes explored remain far from planetary conditions, highlighting challenges for future research in scaling these results to realistic geophysical and astrophysical contexts.