The influence of density variation on shear layer vortex in a jet diffusion flame

単一噴流拡散火炎中に形成されるせん断渦に及ぼす密度変化の影響

The influence of density variation on shear layer vortex in a jet diffusion flame

Creators Kawahara Hideo

Creators Nishimura Tatsuo

The present study treats with the onset of shear layer vortex in a jet diffusion flame and its development. The flow instability of jet depends on the density variation in the combustion field, i.e., heat release and different fuels etc. We perform a direct numerical simulation for two fuels, i.e., CH4 and C3H8 in the Reynolds number of 500 to 3000 based on the exit of fuel injection tube with a diameter of 10mm. The density of C3H8 is larger than that of air, but the density of CH4 is smaller. The flame sheet model of infinite chemical reaction and unity Lewis number are assumed in the simulation. It is found that intermittent shear layer vortex region occurs before periodic vortex region and that the intermittent region for C3H8 appears at a lower Reynolds number than that for CH4. In the periodic vortex region, the vortex for C3H8 changes from outward to inward rotation in the downstream zone of fuel jet, unlike the case of CH4. The vortex frequency is represented in terms of Strouhal number, almost independent of the Reynolds number. Furthermore, the effect of thermal buoyancy outside the flame is examined. It is revealed that a large scale vortex induced by thermal buoyancy enhances the onset of shear layer vortex and maintains the development of periodic vortex.

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