Emergence of Competition between Different Dissipative Structures for the Same Free Energy Source

In this paper, we explore the emergence and direct interaction of two different types of dissipative structure in a single system: self-replicating chemical spot patterns and buoyancyinduced convection rolls. A new Lattice Boltzmann Model is developed, capable of simulating fluid flow, heat transport, and thermal chemical reactions, all within a simple, efficient framework. We report on a first set of simulations using this new model, wherein the Gray-Scott reaction diffusion system is embedded within a non isothermal fluid undergoing natural convection due to temperature gradients. The non-linear reaction which characterises the Gray-Scott system is given a temperature-dependent rate constant of the form of the Arrhenius equation. The enthalpy change (exothermic heat release or endothermic heat absorption) of the reaction can also be adjusted, allowing a direct coupling between the dynamics of the reaction and the thermal fluid flow. The simulations show positive feedback effects when the reaction is exothermic, but an intriguing, competitive and unstable behaviour occurs when the reaction is sufficiently endothermic. In fact when convection plumes emerge and grow, the reaction diffusion spots immediately surround them, since they require a source of heat for the reaction to proceed. Then however, the proliferation of spot patterns dampens the local temperature, eventually eliminating the initial convection plume and reducing the ability of the spots to persist. This behaviour appears almost ecological, similar as it is, to competitive interactions between organisms competing for the same nutrient source.