2003 Volume 45 Issue 133 Pages 177-183
Unstable behavior of premixed flames generated by hydrodynamic and diffusive-thermal effects is studied by two-dimensional unsteady calculations of reactive flows. In the present numerical simulation, the compressible Navier-Stokes equation including a one-step irreversible chemical reaction is employed. We consider two basic types of phenomena to account for the intrinsic instability of premixed flames, i.e., hydrodynamic and diffusive-thermal effects. The hydrodynamic effect is caused by the thermal expansion through flame fronts; the diffusive-thermal effect is caused by the preferential diffusion of mass and heat. A disturbance with several wavelengths is superimposed on a stationary planar flame, and the formation of cellular flames generated by hydrodynamic and diffusive-thermal effects is numerically simulated. After the cellular-flame formation, the division and combine of cells are observed at low Lewis numbers. The cell size changes with time, and its mean value is greater than the critical wavelength. At the Lewis number unity, on the other hand, the division of cells is not observed but the combine is. Thus, the diffusive-thermal effect has an important role in the appearance of unstable behavior of premixed flames. The flame velocity of a cellular flame depends on the length of computational domain. As the domain length increases, the flame velocity becomes larger. This is because the long-wavelength components of disturbances have a great influence on the unstable behavior of cellular flames.
