No abstract

No abstract

No abstract

No abstract

The statistical behaviour of the surface density function (SDF, the magnitude of the reaction progress variable gradient) and the strain rates, which govern the evolution of the SDF, have been analysed using a three-dimensional flame-resolved simulation database of a turbulent lean premixed methane-air flame in a bluff-body configuration. It has been found that the turbulence intensity increases with the distance from the burner, changing the flame curvature distribution and increasing the probability of negative curvature in downstream direction. The curvature dependences of dilatation rate ∇ • ⃗ and displacement speed give rise to variations of these quantities in the axial direction. These variations affect the nature of the alignment between the progress variable gradient and the local principal strain rates, which in turn affects the mean flame normal strain rate, which assumes positive values close to the burner but increasingly becomes negative as the effect of turbulence increases with axial distance from the burner exit. The axial distance dependences of curvature and displacement speed also induce a considerable variation in the mean value of the mean curvature stretch. The axial distance dependences of dilatation rate and flame normal strain rate govern the behaviour of the flame tangential strain rate, and its mean value increases in downstream direction. The current analysis indicates that the statistical behaviours of different strain rates and displacement speed and their curvature dependences need to be included in the modelling of Flame Surface Density and Scalar Dissipation Rate in order to accurate capture their local behaviours.