Large-Scale Flow and Spiral Core Instability in Rayleigh-Benard   Convection
  The 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. 
Igor Aranson (Department of Physics, Bar Ilan University, Ramat Gan),   Michel Assenheimer (Laboratoire de Physique Statisti...