Analysis of Highly-Turbulent Premixed Flames Using a Retrospective Lagrangian Approach

A retrospective (i.e., backwards in time) Lagrangian analysis is used to examine premixed flame structure and dynamics for highly turbulent reactant mixtures. The computational cost of such a retrospective analysis can be enormous due to the associated data storage requirements, but this approach enables the relatively straightforward study of the dynamical origins of transient flame phenomena such as ignition, extinction, and pocket formation. In this talk, we present results from a retrospective Lagrangian analysis performed on data from a direct numerical simulation (DNS) of premixed n-dodecane combustion in an unconfined domain. The turbulence intensity in the DNS is quite high, with Karlovitz numbers of O(10²-10³), resulting in substantial thermochemical complexity. In particular, we show that fuel consumption and temperature rise within fluid parcels are frequently non-monotonic, resulting in frequent cooling events even after the temperature within a parcel has risen to 1400K or more, and we identify the dynamical origins of this non-monotonicity. Complex transient phenomena such as auto- and forced-ignition, extinction, and pocket formation are also identified, and the retrospective Lagrangian analysis is used to examine the dynamics leading to such events.