LES of the Sydney piloted spray flame series with the PFGM/ATF approach and different sub-filter models

Abstract

Detailed numerical investigations of the Sydney spray flame series [1] are presented for ethanol flames referred to as “EtF3, EtF6 and EtF8”, which feature identical ethanol mass flow rates but different carrier gas mass flow rates. Large eddy simulations (LES) are performed, where the gaseous and liquid phases are modeled by an Eulerian/Lagrangian approach. The turbulent sub-filter stresses (sgs) are modeled with Nicoud’s sigma model [2] on grids with two different resolutions. Combustion is modeled with the premixed flamelet generated manifold approach (PFGM), which is combined with the artificially thickened flame (ATF) method. The sub-filter distributions of the control variables are modeled with (a) a β function (β-fdf) and (b) a top-hat function (TH). First, the influence of the variance in the mixture fraction and reaction progress variable is investigated separately, where the variances are either determined from an algebraic model or a transport equation model. Subsequently, the TH model is used to account for the joint impact of Z and Yp. The results are compared against the experimental measurements and reference simulations without sub-filter model. The particle statistics are in good agreement with the experimental data. The variances predicted by the two algebraic models are quite similar, whereas the transport equation model predicts variances which are one order of magnitude higher. The results obtained with the TH and the β-fdf model are comparable. It is found that the impact of the sgs models for the mixture fraction and the progress variable increases with an increasing carrier gas mass flow rate.