A Statistical Study on Surface Properties of Freely-Propagating Premixed Turbulent Flames

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Abstract
This study presents an experimental investigation on the structure of the flame front geometry in the case of unsteady premixed turbulent flames. Methaneair mixtures have been sparked-ignited in a vertical wind tunnel and freely propagate in a grid-generated decaying isotropic turbulent flow. In order to point out the aspects of the mutual interaction between combustion and turbulence, measurements have been performed under varying conditions of turbulence and mixture stoechiometry. The high speed tomography technique has been adapted to follow and describe the temporal evolution of the flame fronts. An extensive use of the computational image processing and analysis techniques has been made to determine the structure and the spatial properties of the expanding flame kernels. Specifically, modifications in flame geometry have been investigated during flame propagation in terms of statistics and probability distributions of local flame front curvature. The mean and rms curvatures, as well as the positive and negative ones, have been calculated along the flame front for different turbulent and chemical conditions. Fractal analysis has also been applied to the flame front length. The influence of the turbulent flow field characteristics and of the equivalence ratio on the fractal dimension, the inner and outer cutoffs have been evaluated versus time. The results has been interpreted and compared with results availabled in the literature.