2005 Volume 47 Issue 141 Pages 220-226
The dynamic behavior of premixed flames propagating in non-uniform velocity fields has been investigated by two-dimensional unsteady calculations of reactive flows, based on the compressible Navier-Stokes equation including a one-step irreversible chemical reaction. We consider two basic types of phenomena to account for the intrinsic instability of premixed flames, i. e., hydrodynamic and diffusive-thermal effects, and examine the influence of intrinsic instability on the dynamic behavior. A sinusoidal disturbance is superimposed on the velocity field of the unburned gas, and its wavelength is set equal to the critical wavelength at Le = 1.0. The behavior of cellular flames generated by a disturbance and by hydrodynamic and diffusive-thermal effects is numerically simulated. When Le = 1.0, at the beginning of calculations, we observe the cellular flames whose wavelength is equal to that of a disturbance. After that, cells combine together and a large cell appears. The wavelength of a large cell is consistent with the size of cellular flames generated only by intrinsic instability. When Le = 0.5, on the other hand, small cells appear, and the division and combination of cells are observed. This is because that the size of cells due to intrinsic instability is shorter than the wavelength of a disturbance. The burning velocity of cellular flames propagating in non-uniform velocity fields is larger than that of planar flames propagating in uniform, which is due to a disturbance and intrinsic instability. The increment in the burning velocity depends not only on the intensity of a disturbance but on the Lewis number.
