Large Eddy Simulation-Based Analysis of Entropy Generation in a Turbulent Nonpremixed Flame

LES (large eddy simulation) is employed for prediction and analysis of entropy generation in turbulent combustion. The entropy transport equation is considered in LES. This equation contains several unclosed entropy generation terms corresponding to irreversible processes: heat conduction, mass diffusion, chemical reaction and viscous dissipation. The SGS (subgrid scale) closure of these effects is provided by a methodology termed the En-FDF (entropy filtered density function), which contains complete statistical information about SGS variation of scalars and entropy. In the En-FDF, the effects of chemical reaction and its associated entropy generation appear in closed forms. The methodology is applied for LES of a nonpremixed jet flame. Predictions show good agreements with the experimental data. Analysis of entropy generation shows that heat conduction and chemical reaction are the main sources of irreversibility in this flame. The sensitivity of individual entropy generation effects to turbulence intensity is studied.