Investigation of Entrainment and its Effect on Flame Stabilization in a Turbulent High Karlovitz Number Premixed Jet Flame using Direct Numerical Simulation

Abstract

The stabilization of high Karlovitz number (Ka) jet flames is challenging due to the strong mean shear, and the role of entrainment on high Ka flame stabilization is not well understood. In the present work, a direct numerical simulation study of fluid entrainment and its effect on the flame stabilization in a three-dimensional turbulent high Ka premixed jet flame with a strong mean shear was carried out. The global entrainment characteristics in the turbulent jet flame was analyzed, which shows that the mass flow of the jet increases almost linearly with the streamwise distance. The turbulent/non-turbulent (T/NT) interface was investigated and the conditional statistics near the T/NT interface were analyzed. It was found that the enstrophy transport is generally balanced by the vortex stretching term and the viscous dissipation term. In the region close to the interface, the enstrophy generation from the viscous diffusion term is dominant, which has significant impact on the T/NT interface propagation. Overall, the T/NT interface propagates towards the non-turbulent region. Therefore, the species in the coflow of the non-turbulent region are entrained into the turbulent region across the T/NT interface. Various terms of species transport equations conditioned on the T/NT interface were analyzed. It was concluded that the entrainment of species such as OH plays an important role in flame stabilization in the upstream region.