Darrieus-Landau instability effect on the flame topology and brush thickness for premixed turbulent flames

The effect of Darrieus-Landau (DL) instability on flame topology and brush thickness was systematically investigated on a planar and Bunsen flame, with the latter used for direct comparison with experimental results from PLIF technique. For planar flame, the flame brush thickness significantly increases with turbulence intensity v', then the increase slows down and finally levels off to a certain value for all cases. This is tributed to the fact that DL instability plays a primary role on flame topology at weak turbulence intensities while this effect is shaded by turbulence perturbation at high intensities ultimately leading to an indistinguishable flame brush. In Bunsen configuration, flame fluctuations are superimposed on an average conical flame. The brush thickness shows a monotonous increase with downstream distance and follows the linear relation as predicted by Taylor's diffusion law. The centerline flame brush thickness significantly increases with v' at weak intensity range and then levels off to a constant value with sub-critical flame being thicker, which is opposite with planar flame. The normalized value collapses to a common curve, indicating this can be an appropriate parameter for Bunsen flame. The good qualitative match with C3H8/air flames indicates the prediction capabilities of the hydrodynamic model.