Body-force effect on the lateral movement of cellular flames at low Lewis numbers.

The body-force effect on the lateral movement of cellular flames is studied by unsteady calculations of reactive flows at low Lewis numbers. We employ the compressible Navier-Stokes equation including chemical reaction to take account of the hydrodynamic effect caused by thermal expansion. A sinusoidal disturbance with the linearly most unstable wavelength is superimposed on a plane flame to simulate the formation of a cellular flame. The superimposed disturbance grows initially with time, and then the flame front changes from a sinusoidal to a cellular shape. After the cell formation, the cellular flame moves laterally at Lewis numbers lower than unity. The reason is that the diffusive-thermal effect, and the nonlinear effect of the flame front, play a primary role in the appearance of the lateral movement of cells. The body-force effect has a great influence on the lateral velocity of cells. When flames are propagated upward, the lateral velocity decreases as the acceleration increases, even though the body-force effect has a destabilizing influence. When flames are propagated downward, on the other hand, the lateral velocity takes a maximum value at the specific acceleration and decreases with an increase in acceleration. The dependence of lateral velocity on the acceleration is due to the augmentation and diminution in maximum flame temperature and to the broadness and narrowness of a high-temperature region behind a convex flame front.