Subgrid-scale mixing of mixture fraction, temperature, and species mass fractions in turbulent partially premixed flames

Abstract

The subgrid-scale (SGS) mixing of mixture fraction, temperature, and species mass fraction in turbulent partially premixed (Sandia) flames is studied. We focus on the effects of the SGS mixing regimes and the spatial relationships among the scalars on the SGS mixing of the species mass fractions. High-resolution lines images are used to obtain the scalar filtered mass density function and the conditionally filtered diffusion. The results show that for small SGS variance the scalar fields have a relatively simple structure. For large SGS variance the structure is more complex. The spatial relationships among the scalars result in different SGS scalar structures and SGS mixing characteristics, with the mass fraction of CO2 being the simplest and that of CO being the most complex. The results in this study present a challenging test for SGS mixing models.