Investigations of the extended Eddy Dissipation Concept formulation for weakly turbulent and slow chemistry flames

Abstract

Recent extensions of the Eddy Dissipation Concept (EDC) are investigated with the purpose of analysing the importance of model limiters to the EDC performance when predicting Moderate and Intense Low-oxygen Dilution (MILD) flames. These limiters are associated with the mass fraction of fine structure regions, turbulence Damköhler number (Da), and turbulence Reynolds number (Re). The method is Reynolds Averaged Navier Stokes computation using OpenFOAM v.7 combined with the modified steady-state solver edcSimpleSMOKE. The results show that increasing the upper limit of fine structure region close to unity influences flame temperature, which could critically affect the turbulence Da and Re fields. The minimum constraint of turbulence Da plays a significant role in distributing reaction, thus imitating the behaviour of MILD flames. Tuning this constraint is also crucial for the accuracy of the model extension since it can allow nullifying or maximising modification effects for weakly turbulent and slow chemistry flames. The limit of turbulence Re is analysed in relation to turbulence modelling. Evaluation against a conventional turbulent flame demonstrates that the extended EDC underpredicts turbulence Da field, allowing similar modification to that applied in MILD condition.