DYNAMICS OF ENSTROPHY AND TURBULENT KINETIC ENERGY IN TURBULENT PREMIXED FLAMES AT HIGH PRESSURE

In this study, we examine the effects of pressure and characteristic scales on the dynamics and transport of turbulent kinetic energy (TKE) and enstrophy within freely propagating methane/air turbulent premixed flames. We analyze five high-fidelity direct numerical simulation (DNS) datasets where the cases differ in pressure (1 and 10 atm) and Karlovitz number (18-260). For the analysis of TKE, we examine the variation of spectral kinetic energy (SKE) and the terms contributing to it across the flame brush region. These terms include nonlinear advection processes, pressure gradient, shear viscous diffusion, and dilatation viscous diffusion. The results show that the contribution to the SKE is largest by the shear viscous diffusion and smallest by the nonlinear advective processes. With an increase in the pressure, the contribution of all terms except the advection term tends to increase across the range of scales. The analysis of enstrophy and the four terms contributing to it, which include vortex stretching, dilatation, baroclinic torque, and viscous dissipation, show the dominant positive and negative contributions by the vortex stretching and dissipation terms, respectively. The baroclinic torque contributes positively to the enstrophy, whereas the dilatation term shows both positive and negative contributions within the flame brush region. The normalization of the terms based on characteristic small scales shows that although the qualitative variation in the state-space of the term is similar in all cases, there are quantitative differences, which can be attributed to the effects of differences in pressure and a low Karlovitz number in some of the cases.