Leading edge statistics of turbulent, lean, H2–air flames

Abstract Several studies have utilized leading points concepts to explain the sensitivity of turbulent burning rates to fuel/oxidizer composition, especially in negative Markstein length mixtures. Leading point theories suggest that the premixed turbulent flame speed is controlled by the flame front characteristics at the flame brush leading edge, or, in other words, by the flamelets that advance farthest into the unburned mixture (the so-called leading points). Furthermore, several authors have postulated that these leading edge flamelets have an inner structure similar to a critically perturbed laminar flame, i.e., the local stretch rate approaches the extinction value, near where the maximum possible laminar burning velocity is reached. In order to investigate these hypotheses for leading points burning rates, this paper analyzes the flame front structure at the leading edge of turbulent, lean ( ϕ  = 0.31) premixed H 2 /Air flames, utilizing a database of direct numerical simulations (DNS) previously reported by Aspden et al. (2011). We calculate local flame front curvature, thickness, and burning velocity and compare these values to reference quantities obtained from stretched laminar flames computed numerically in different geometrical configurations (a counterflow twin flame, a tubular counterflow flame and an expanding cylindrical flame). These comparisons show that curvatures and burning velocities approach those of “critically” stretched laminar flames for the highest turbulent intensity case, but not for the lower turbulence intensity cases. In all cases, however, the structure of the flame front at the leading edge seems to closely mirror laminar flame calculations.