Hierarchical Structure of Spiral Flow-Waves Self-Organized in a Reaction-Diffusion-Convection System and Its Gravity Effect

点击翻译按钮获取中文摘要

In this study, we investigated a mechanism to self-organize convective structures such as spiral flow waves in a solution layer of Belousov-Zhabotinsky (BZ) reaction exciting spiral chemical waves. Two main approaches are 1)numerical experiments to simulate the convective structures by introducing an elastic surface model in the reaction-diffusion and convection system., and 2)micro-gravity experiment of the flow waves. The latter experiment was supported by Japan Space Forum. 10 times of micro-gravity experiment were carried out at a fall tower in MGLAB (Toki city). The fall tower provides 4 seconds environment of micro-gravity. Several new findings were obtained on the convective pattern formation accompanied by chemical waves under micro-gravity condition.In the previous studies, we have been clarified : curious phenomena. These are1)Apropagating convection associated with a single chemical wave triggered in an excitable BZ-solution having a free water-air surface.(1988),2)An accele … More rating chemical wave propagation accompanied by a strong convection (A Big Wave, 1993),3)An oscillatory flow appeared in the solution layer exciting spiral chemical waves (1988), and4)A propagating flow wave self-organized in the BZ-solution exciting spiral chemical waves (1995, by Matthiessen and Muller), and spiral-shaped flow wave with rotating pattern dynamics (2003).All of the above phenomena were found by our research group excepting for the propagating flow wave. Previous studies of numerical experiments never succeeded to explain these phenomena even for the simplest case of the propagating convection accompanied by the single chemical wave. A simple model of reaction-diffusion and convection system is hard to explain a long roll-shaped convective structure appeared in front of the single chemical wave.We proposed a new model of the reaction-diffusion and convection system. The model assumes that the top surface of a shallow layer of a chemical solution has an elastic property. A concentration gradient of chemical species induces displacement of the elastic surface through the Marangoni convection. A one-dimension model proposed here connects the Oregonator model with an elastic equation describing displacement of the top surface. The model successfully reproduces surface flow structures organized in the BZ solution layer exciting the single chemical wave and a chemical wave train. In addition, a two-dimensional model, which connects the one-dimensional model with the Navier-Stokes equations describing convective flow in the bulk of the chemical solution, also reproduces plausible flow structures, compared with the previous model (Matthiessenn et al., 1996).We also carried out a series of micro-gravity experiment at the fall tower in MGLAB. To clarify the gravity effect on the convective pattern formation associated with chemical waves, 10 times micro-gravity experiments were repeated. As the results we obtained new findings as follows:1)Chemical wave experiment under micro-gravity is possible even in a vessel having a free air-water surface by keeping a hydrophilic condition at the bottom surface of the vessel,2)A deformation of liquid surface under micro-gravity can be suppressed by controlling the surface condition of hydrophilic or hydrophobic at the side of the vessel,3)During micro-gravity, the chemical waves seemed to be deformed by some convective effects,4)Optical interference experiment to analyze surface deformation was possible until just before the free fall. Less