Dissipation element analysis of a turbulent non-premixed jet flame

Abstract

The objective of the present work is to examine the interaction between turbulent mixing and chemistry by employing the method of dissipation elements in a non-premixed turbulent jet flame. The method of dissipation elements [L. Wang and N. Peters, J. Fluid Mech. 554, 457–475 (2006)] is used to perform a space-filling decomposition of the turbulent jet flow into different regimes conditioned on their location with respect to the reaction zone. Based on the non-local structure of dissipation elements, this decomposition allows us to discern whether points away from stoichiometry are connected through a diffusive layer with the reaction zone. In a next step, a regime based statistical analysis of dissipation elements is carried out by means of data obtained from a direct numerical simulation. Turbulent mixing and chemical reactions depend strongly on the mixture fraction gradient. From a budget between strain and dissipation, the mechanism for the formation and destruction of mean gradients along dissipation elements is inspected. This budget reveals that large gradients in the mixture fraction field occur at a small but finite length scale. Finally, the inner structure of dissipation elements is examined by computing statistics along gradient trajectories of the mixture fraction field. Thereby, the method of dissipation elements provides a statistical characterization of flamelets and novel insight into the interaction between chemistry and turbulence.