Effect of turbulence characteristics on local flame structure of H2-air premixed flames

Abstract

Direct numerical simulations (DNS) of turbulent premixed flames are conducted to investigate effects of turbulence characteristics on the local flame structure. A detailed kinetic mechanism including 12 reactive species and 27 elementary reactions is used to represent the H2–air reaction in turbulence. Numerical conditions of DNS can be classified into a wrinkled-flamelets regime, a corrugated-flamelets regime and thin reaction zones near the boundary of Karlovitz number Ka = 1.0 of the turbulent-combustion diagram. For all cases, the distribution of heat-release rate shows a three-dimensionally connected sheet-like feature, even though the heat-release rate highly fluctuates along the flamefront. The heat-release rate tends to increase at the flamefronts that are convex towards the burnt side. For the turbulent premixed flames in the corrugated-flamelets regime, the handgrip structure is produced by the intrusion of the coherent fine-scale eddy into the flame and the heat-release rate in this structure increases up to 1.2 times of that of a laminar flame. In the wrinkled-flamelets regime, the spire-like structure of the flamefront is created due to the coherent fine-scale eddies in turbulence. By identifying flame elements in turbulence, their statistical characteristics are also discussed. This paper was chosen from Selected Proceedings of the Third International Symposium on Turbulence and Shear Flow Phenomena (Sendai, Japan, 24–27 June 2003). E-mail: mtanahas@mes.titech.ac.jp