Fractal scaling of turbulent premixed flame fronts: Application to LES

• We experimentally and numerically investigate the fractal features of turbulent premixed flame fronts.
• The fractal dimension is found to be around 2.23 despite the level of turbulence intensity.
• The inner cut-off length where the fractal scaling is lost is found to scale with the Kolmogorov length.
• The LES model built exploiting these fractal features shows remarkable performance.

The fractal scaling properties of turbulent premixed flame fronts have been investigated and considered for modeling sub-grid scales in the Large-Eddy-Simulation framework. Since the width of such thin reaction fronts cannot be resolved into the coarse mesh of LES, the extent of wrinkled flame surface contained in a volume is taken into account. The amount of unresolved flame front is estimated via the “wrinkling factor” that depends on the definition of a suitable fractal dimension and the scale at which the fractal scaling is lost, the inner cut-off length ∊i∊i. In this context, the present study considers laboratory experiments and one-step reaction DNS of turbulent premixed jet flames in different regimes of turbulent premixed flames. Fractal dimension is found to be substantially constant and well below that typical of passive scalar fronts. The inner cut-off length shows a clear scaling with the dissipative scale of Kolmogorov for the regimes here considered. These features have been exploited performing Large Eddy Simulations. Good model performance has been found comparing the LES against a corresponding DNS at moderate Reynolds number and experimental data at higher Reynolds numbers.