Outwardly growing premixed flames in turbulent media

Abstract

The propagation of outwardly expanding premixed flames in turbulent media is examined within the context of the hydrodynamic theory wherein the flame, treated as a surface of density discontinuity separating fresh combustible mixture from burned products, is propagating at a speed dependent upon local geometric and mixture/flow characteristics. An embedded manifold approach, one adept at handling multi-valued and disjointed surfaces which are frequently observed in real flames, is used to couple the flow and flame evolution. A sensitivity analysis, based on mixtures with different Markstein numbers, is performed to investigate early flame kernel development in addition to its long-term evolution. The focus is to understand the effect of turbulent flow characteristics, distinguished by the intensity of velocity fluctuations and its integral length scale, in addition to intrinsic flame instabilities (predominantly the Darrieus-Landau instability) on flame propagation. The overarching objective is to quantify their influence on the flame morphology and burning rate and to construct scaling laws for the turbulent flame speed through appropriate modifications of Damköhler’s first hypothesis. Flame-turbulence interactions are inferred from statistical quantities based on its developing flame topology, including local flame curvature and hydrodynamic strain, and their combined effects integrated into the flame stretch rate experienced by the flame and the local flame speed deviation from the laminar flame speed.