Effects of the subgrid-scale mixture fraction structure on scalar and temperature dissipation in turbulent partially premixed flames Conference Paper uri icon

abstract

  • The subgrid-scale (SGS) mixture fraction has recently been shown to have different structures and distributions for different SGS scalar variances. We study the effects of the structures on the scalar dissipation and temperature dissipation in the context of large-eddy simulation of turbulent combustion. Line images obtained in turbulent partially premixed flames are used to analyze the scalar and temperature dissipation rates conditional on the scalar and temperature. The results show that for fully burning SGS scalar fields, the SGS scalar with small SGS variance, which is well mixed, results in scalar and temperature dissipation structures consistent with the quasi-equilibrium distributed reaction zones. For large SGS variance, the SGS scalar, which is nonpremixed, results in those consistent with strained laminar flamelets. For extinguished SGS scalar fields, in the well mixed SGS mixture fraction the scalar and temperature dissipation structures are similar and are consistent with extinguished distributed reaction zones. In the nonpremixed SGS scalar fields the scalar and temperature dissipation structures are different, highlighting the effects of turbulence-chemistry interaction on the temperature dissipation. The SGS mixing time scales for the mixture fraction and temperature increase with the SGS scalar variance. The results in the present study show that it is important for combustion models to predict both distributed reaction zones and flamelets as well as their extinction. Specifically, mixing models for FDF methods need to be able to account for the different SGS temperature structures and the SGS mixing time scales resulted from the different SGS mixture fraction structures.

author list (cited authors)

  • Wang, D., Tong, C., Barlow, R. S., & Karpetis, A. N.

publication date

  • January 2007