title: Streamline segment statistics of premixed flames with nonunity Lewis numbers.
abstract: The interaction of flame and surrounding fluid motion is of central importance in the fundamental understanding of turbulent combustion. It is demonstrated here that this interaction can be represented using streamline segment analysis, which was previously applied in nonreactive turbulence. The present work focuses on the effects of the global Lewis number (Le) on streamline segment statistics in premixed flames in the thin-reaction-zones regime. A direct numerical simulation database of freely propagating thin-reaction-zones regime flames with Le ranging from 0.34 to 1.2 is used to demonstrate that Le has significant influences on the characteristic features of the streamline segment, such as the curve length, the difference in the velocity magnitude at two extremal points, and their correlations with the local flame curvature. The strengthenings of the dilatation rate, flame normal acceleration, and flame-generated turbulence with decreasing Le are principally responsible for these observed effects. An expression for the probability density function (pdf) of the streamline segment length, originally developed for nonreacting turbulent flows, captures the qualitative behavior for turbulent premixed flames in the thin-reaction-zones regime for a wide range of Le values. The joint pdfs between the streamline length and the difference in the velocity magnitude at two extremal points for both unweighted and density-weighted velocity vectors are analyzed and compared. Detailed explanations are provided for the observed differences in the topological behaviors of the streamline segment in response to the global Le.
authors.affiliation: School of Mechanical and Systems Engineering, Newcastle University Claremont Road, Newcastle-Upon-Tyne NE1 7RU, UK.
authors.forename: Nilanjan
authors.initials: N
authors.lastname: Chakraborty
authors.affiliation: UM-SJTU Joint Institute, Shanghai JiaoTong University, Shanghai 200240, China.
authors.forename: Lipo
authors.initials: L
authors.lastname: Wang
authors.affiliation: Universität der Bundeswehr München, Werner-Heisenberg-Weg 39, 85577 Neubiberg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Klein