THEORETICAL MODELING OF SPIRAL CHAOS IN RAYLEIGH-BENARD CONVECTION

The spiral chaos state recently observed in Rayleigh-Benard convection is studied using the long wave length phase equation and numerical si mulations of two-dimensional equations modelling the pattern formation in convection. The phase equation description of a single spiral, whi ch may also be investigated experimentally, shows that the motion is d ominated by wave vector frustration, rather than the rotational motion driven by a vertical vorticity field. This leads to a continuum of sp iral frequencies in the spiral chaos state, and a spiral may rotate in either sense depending on the wave vector of its local environment. T he formation of the spiral chaos state is understood in terms of invas ive defects, i.e. defects that through their intrinsic dynamics expand to take over the system. Numerical simulations of the chaotic state a s a function of the model parameters provide confirmation of these res ults. In addition the mechanisms of spiral creation and destruction, t he axisymmetric target to spiral transition, and a novel core oscillat ion, are described.