Effects of molecular transport in LES/PDF of piloted turbulent dimethyl ether/air jet flames

Abstract

We report large-eddy simulation (LES)/probability density function (PDF) modeling of piloted turbulent dimethyl ether (DME)/air jet flames with a skeletal chemical mechanism. The modeled PDF transport equation with three different implementations of molecular transport in the interaction-by-exchange-with-the-mean (IEM) mixing model is solved using the NGA/HPDF code in order to assess the a posteriori performance of these LES/PDF methodologies applied to the DME flames D and F proposed in the TNF Workshop. The three implementations considered are the classical random-walk model (IEM-RW), the mean-drift model with a single molecular diffusivity (IEM-MD), and the mean-drift model with differential diffusion (IEM-DD). Better quantitative agreement with experimental data for the mean and root-mean-square profiles of mixture fraction, temperature and major species mole fractions and conditional means on mixture fraction are obtained with the IEM-MD model than with the IEM-RW model. In LES of the DME flame series, the molecular diffusivity dominates the turbulent diffusivity in the centerline region, so the accurate modeling of molecular transport plays a significant role in LES/PDF of these jet flames. Nevertheless, the IEM-DD model shows only minor effects on the model predictions compared to IEM-MD in these DME flames.