Quantification of the flame structure at multi-scale levels

Abstract

The interaction between flame and turbulence leads to the complex flame topology at multiple scales. In this work, the non-local statistical features of the flame surface topology in turbulent premixed combustion are investigated by using the dissipation element (DE) analysis. Considering a spatial point on the flame front, the gradient trajectory of the flame curvature reaches a local maximum curvature point and a local minimum curvature point along the ascending and descending directions, respectively. A DE is the patch consisting of the points whose gradient trajectories share the same pair of extremal points. The characteristic parameters are chosen as the distance and the curvature difference between two extremal points of each DE. Multi-scale DEs can also be defined to improve the understanding of the turbulent premixed flame surface topology at various scales by extending the extremal points at different scale levels. The results show that the turbulence intensity determines the flame corrugation and consequently the number of DEs, whereas the probability density functions of the normalized length scale of DEs remain unchanged. The conditional mean of the curvature difference with respect to the length scale is strongly dependent on the influence of turbulence on the flame, i.e., that scaling slope decreases with an increase in the turbulence intensity. However, for a given turbulence intensity, the scaling slopes of such conditional mean remain unchanged in different scale brackets.