In turbulent reacting flows, soot evolution is strongly influenced by small-scale soot–turbulence–chemistry interactions. Specifically, soot is formed during combustion of fuel-rich mixtures and, in non-smoking flames, is rapidly oxidized at slightly fuel-rich mixtures before being transported by turbulence into fuel-lean mixtures. Furthermore, different soot evolution mechanisms are dominant over distinct regions of mixture fraction. For these reasons, a new subfilter PDF is proposed to account for this distribution of soot in mixture fraction space. In this model, the sooting mode of a soot subfilter PDF is locally activated only at fuel-rich mixture fractions where surface growth is locally faster than oxidation. This model is first validated a priori against a recent DNS database of a turbulent nonpremixed jet flame. Compared to a subfilter PDF model without any mixture fraction dependence, a significant decrease in the oxidation source term is observed, while the surface growth source term remains hardly affected. This new model is implemented within a Large Eddy Simulation (LES) framework, applied to two laboratory-scale turbulent nonpremixed sooting jet flames, and validated via comparisons with experimental measurements of time-averaged centerline temperature and soot volume fraction. Both the new model and the previous model predict the temperature fairly well. However, compared to the previous model, the soot volume fraction predicted by the new model is significantly increased and in much better agreement with the experimental measurements. In addition, the sensitivity to the subfilter PDF is significantly greater than the sensitivity to grid resolution and is greater or at least comparable to the sensitivity to chemical mechanism.
|Original language||English (US)|
|Number of pages||14|
|Journal||Combustion and Flame|
|State||Published - Nov 2019|
Bibliographical noteFunding Information:
The authors gratefully acknowledge funding from NASA under grant NNX16AP90A . The authors also acknowledge valuable support in the form of computational time on the TIGRESS high performance computer center at Princeton University, which is jointly supported by the Princeton Institute for Computational Science and Engineering (PICSciE) and the Princeton University Office of Information Technology’s Research Computing department.
- Large Eddy Simulation (LES)
- Presumed subfilter PDF
- Soot–turbulence–chemistry interactions