Flame-vorticity interactions in DNS of a turbulent premixed flame stabilized over a backward facing step*

Recirculation zones are often used to stabilize flames in high speed combustion, e.g. gas turbine and scramjet engines. In this work, a direct numerical simulation of a lean ethylene-air turbulent premixed flame, stabilized over the recirculation zone in a backward facing step configuration, is performed to study the interactions between the flame and the shear layer vorticity. Results show that the recirculation zone transports necessary hot radicals such as OH from the downstream region to the stabilization point. Periodic vortex shedding from the corner of the step, observed in the non-reacting flow, is absent in the presence of a flame. The vorticity which is present mainly on the reactant side of the flame near the stabilization point, gets advected into the products downstream. This leads to an enhanced heat transfer from the flame to the wall, and affects the CO and OH oxidation. Statistics of the enstrophy budget as a function of progress variable and streamwise distance will be presented. The turbulent flame structure, which is a function of the streamwise distance, will be compared to the laminar flame to identify the regions of flame thickening, arising due to the interaction with sheared turbulence.