| Summary: | Unstable behaviors of cellular premixed flames caused by hydrodynamic and diffusive-thermal instabilities under high- and low-temperature environment were studied numerically. Unsteady reactive flow was calculated in large space, based on the compressible Navier-Stokes equation including chemical reaction. As the unburned-gas temperature became higher (lower), the growth rate increased (decreased) and the unstable range widened (narrowed), which was due to the enlargement (reduction) of the burning velocity of a planar flame. On the other hand, the normalized growth rate decreased (increased) and the normalized unstable range narrowed (widened) under the high (low) temperature conditions. This was due to the weakness (strength) of thermal-expansion effects and to the reduction (enlargement) of Zeldovich numbers. Furthermore, unstable behaviors of cellular flames, i.e. the coalescence and divide of cells, appeared owing to hydrodynamic and diffusive-thermal instabilities. We found that the burning velocity of a cellular flame changed drastically with time, and the average burning velocity of a cellular flame normalized by that of a planar flame decreased (increased) as the unburned-gas temperature became higher (lower). In addition, the burning velocity of a cellular flame depended strongly on the space size. As the space size became larger, the burning velocity increased monotonously. This was because that the long-wavelength components of disturbances played a significant role in the dynamics of cellular premixed flames.
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