Numerical Simulation on the Intrinsic Instability of High-Temperature Premixed Flames Under the Constant-Enthalpy Conditions

Abstract

The effects of the unburned-gas temperature on the intrinsic instability of high-temperature premixed flames under the constant-enthalpy conditions were studied by two-dimensional unsteady calculations of reactive flows. A sinusoidal disturbance with sufficiently small amplitude was superimposed on a planar flame to obtain the relation between the growth rate and wave number, i.e. the dispersion relation. The growth rate increased as the unburned-gas temperature became higher, which was due to the increase in burning velocity of a planar flame. The linearly most unstable wave number, i.e. the critical wave number, was almost constant, indicating that the cell size was independent of the unburned-gas temperature. To elucidate the characteristics of cellular flames induced by intrinsic instability, a sinusoidal disturbance with the critical wave number was superimposed. The superimposed disturbance evolved, and a cellular-shaped front formed. As the unburned-gas temperature became higher, the behavior of cellular flames became milder, even though the growth rate increased. This was because that the difference in temperature between burned and unburned gases decreased owing to the constant-enthalpy conditions.