Flame brush thickness of premixed turbulent flames: Hydrodynamic theory versus experiments

The effect of varying turbulence intensities on the flame brush thickness is investigated numerically using a hybrid Navier-Stokes/front-tracking methodology in the context of the hydrodynamic theory. Two configurations, namely planar and Bunsen, are chosen with the latter used for direct comparison with experimental OH-PLIF Bunsen flame images. The Darrieus-Landau influences are controlled through the mixture Markstein length and the flame brush is analyzed under two regimes, sub- and supercritical based on the absence/presence of the hydrodynamic instability. In the planar configuration at low intensities, the sub-critical flame brush retains its near flat shape, while the super-critical flame brush forms a highly corrugated structure reminiscent of the cusped-like flames that result in the laminar setting. With increasing turbulence levels, these effects start to gradually diminish as the flame becomes dominated by velocity fluctuations arising from the turbulent field, finally leading to nearly identical behavior in both regimes for very high intensities. Unlike the planar flame, the sub-critical Bunsen flame surface is dominated by large wrinkles with a more rounded shape while the super-critical flame highlights the formation of cusp-like structures on its surface. Numerical verification of the Bunsen flame brush thickness shows a good qualitative match with experimental tests for turbulent CH4/air flames. The good agreement indicates the qualitative prediction capabilities of the hydrodynamic model.