Numerical simulation of an open premixed turbulent V-flame using contour advection with surgery : determination of flame surface density and overall burning rate

Abstract

An open turbulent premixed V-flame is simulated successfully with a robust scheme termed Contour Advection with Surgery. Numerical experiments were performed for both non-reacting and reacting case. In the non-reacting case, comparison with measurements obtained in laboratory studies indicates that the computed integral length scale tends to be larger. However the qualitative trend of evolution of the length scale in the axial direction was similar. In the reacting case, local flame structure is characterized in terms of turbulent flame brush, orientation factor, and the determination of the flame surface density ε. It was noted that velocity fluctuations, flame brush thickness and mean orientation factor all increase with increasing turbulence: The flame surface density profiles were found to be lower at higher turbulence and skewing towards the burnt side was observed. It was also found that maximum flame surface density decreases non-linearly with upstream turbulence whereas the overall burning rate increases non-linearly with upstream turbulence. The values of Bray number NB was also determined for different cases in the simulation and it was observed that NB decreases with the ratio u'/SL. Comparison was made with measurements obtained in laboratory experiments and the agreements are good in general. Values of ε obtained from using the average flame length and flame zone area and the BML formulation are very similar in general but the discrepancy does appear to grow slightly with increasing turbulence intensity. Although it has been proven that there is a finite probability of obtaining |σc| = 0 in the experimental data, the overall burning rate does not seem to be severely affected by assuming the contribution of these parallel flame fronts to be negligible.