拡散・熱的および流体力学的不安定性のスケール効果

抄録

The damage caused by an accidental gas explosion, for example the maximal blast pressure, is strongly influenced by the flame propagation velocity during the explosion. The flame propagation during an explosion is significantly affected by flame instability, and it is known that the flame propagation velocity has certain scale dependency. This study investigates scale effects of diffusive-thermal and hydrodynamic instability by numerically solving the Sivashinsky equation. The following four conditions are considered: a purely diffusive-thermally unstable flame, a purely hydrodynamically unstable flame, a flame that is diffusive-thermally stable but hydrodynamically unstable, and a flame that is unstable both diffusive-thermally and hydrodynamically. It is found that diffusive-thermal instability mainly influences the flame wrinkle structure of a specific wavelength, while hydrodynamic instability influences the largest structure. Thus, hydrodynamic instability shows scale dependency. The fractal dimensions of the flames, which can be used to estimate the flame propagation velocity during an explosion, are computed by two different methods: a Fourier analysis and a method based on the scale dependency of flame propagation velocity. The both methods yield consistent results, and it is found that the fractal dimension mainly depends on the thermal expansion ratio; its dependency on the Lewis number is rather weak.