Analysis of flame surface normal and curvature measured in turbulent premixed stagnation-point flames with crossed-plane tomography

摘要

An analysis is presented in this paper for flame surface normal and curvature measured in three-dimensional space. Three turbulent premixed stagnation-point flames of varied Markstein numbers have been investigated. Generalized forms of the probability density functions (pdf's) are proposed for flame crossing angle and surface curvature. The pdf of the crossing angle provides a robust way of deriving the ratio of mean wrinkled flame surface area to the flame brush area, A_T/A_L. Values of A_T/A_L have been compared with the turbulent consumption and turbulent displacement speeds measured with particle image velocime-try (PIV). The dependency of A_T/A_L on flame/flow parameters has also been clarified. Similar probability density distributions are found for two- and three-dimensional flame curvatures. The tail approximation however is far from that of a Gaussian function, but exhibits an exponential behaviour at extreme curvatures. Cusp formation and thermo-diffusive instability are identified as the two major factors that drive the curvature distribution asymmetric.