A priori and a posteriori studies of a novel spray flamelet tabulation methodology considering evaporation effects

Abstract

Turbulent spray flames are complicated combustion configurations involving many coupled processes including atomization, evaporation, mixing, chemical reactions, etc. Different flamelet models with intrinsically high computational efficiency have been proposed and extended to model spray combustion. One popular approach for flamelet modeling is based on the gaseous flamelet library, but the accuracy is not guaranteed for combustion with gas–liquid two-phase flows. The other approach is based on the spray flamelet library that takes into account the effects of evaporation on the flamelet structure, but problems related to the non-monotonicity of mixture fraction occur. We develop a novel tabulated spray flamelet/progress variable (TSFPV) model in the present work. An additional mixture fraction Zcarr (named carrier mixture fraction) is defined to describe the mixing process, and it proves to avoid the problem of non-monotonicity of the spray flame structure. The empirical formulas of mass and energy evaporation source terms are obtained and then applied to one-dimensional flames in order to create the flamelet library considering evaporation effects. The developed TSFPV model is validated via simulations of laminar spray counterflow flame and turbulent spray reactive jet in cross-flow, where strong interactions between spray droplets and flame occur and the traditional Flamelet/Progress Variable (FPV) model fails. The a priori and a posteriori studies of TSFPV model are conducted, and the model shows to achieve good agreement with the detailed chemistry solutions. The double-reaction spray flame structure can be captured correctly. The TSFPV model can also give sound quantitative predictions for temperature and minor intermediate products (such as OH, C2H2, and C2H4).