Premixed flame effects on turbulence and pressure-related terms

Direct numerical simulations (DNS) were carried out for premixed, turbulent flames. Heat release effects are accounted for by inclusion of variable density. The simulated flames are thin in the sense that the reaction progress variable is bi-modal and consistent with BML theory. The DNS data were used for detailed study of flame effects on turbulence within the turbulent flame brush by examining the turbulent kinetic energy budget. The flame effects on turbulent kinetic energy were found to depend strongly on the heat release. Both mean and fluctuating pressure terms were found to be the main factors responsible for increases in turbulent kinetic energy. The main sinks for turbulence are dissipation and mean dilatation. Pressure diffusion was found to dominate the other turbulent kinetic energy diffusion terms. A model was developed for pressure dilatation that matches the DNS results very closely. The model indicates that pressure dilatation will remain an important source of turbulence even as heat release increases.