2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/153223The spiral core instability, observed in large aspect ratio Rayleigh-Benard convection, is studied numerically in the framework of the Swift-Hohenberg equation coupled to a large-scale flow. It is shown that the instability leads to non-trivial core dynamics and is driven by the self-generated vorticity. Moreover, the recently reported transition from spirals to hexagons near the core is shown to occur only in the presence of a non-variational nonlinearity, and is triggered by the spiral core instability. Qualitative agreement between the simulations and the experiments is demonstrated.ReVTeX, 10 pages, 6 EPS Figures, submitted to Phys. Rev. LettPattern Formation and Solitonstext