Influence of wrinkled premixed-flame dynamics on large-scale, low-intensity turbulent flow

Abstract

Premixed turbulent flame propagation is analysed under the assumptions of stationarity and transverse homogeneity by expansions for small values of the ratio of the turbulence intensity to the laminar burning velocity. For large Zel'dovich numbers, the effects of diffusive—thermal phenomena within the flame, gas expansion, buoyancy and Lewis and Prandtl numbers different from unity are taken into account under the constraint that turbulence scales are large compared with the laminar flame thickness. A general formulation is given, involving solutions through Fourier decompositions. Parametric results for turbulent burning velocities are obtained, and the evolution of components of turbulent kinetic energies through the flame is calculated. It is shown how buoyancy counteracts the tendency for gas expansion to increase transverse components of the turbulent kinetic energy, pressure fluctuations and vorticity generation across the wrinkled flame. Strong readjustments in components of the turbulent kinetic energy are shown to occur in the downstream hydrodynamic zone. It is established that, with the effects of the hydrodynamic zones fully taken into account, the flame can induce anisotropy in initially isotropic turbulence such that the final velocity fluctuations exhibit higher intensities in the longitudinal mode than in transverse modes, while the enhanced vorticity fluctuations are entirely transverse.