Evaluation of radiation modeling approaches for non-premixed flamelets considering a laminar methane air flame

Based on the validated CFD results the main focus is to analyze the applicability of radiation modeling approaches within the flamelet framework for unity Lewis number and differential diffusion. An unsteady Lagrangian flamelet model with direct integration of the radiation source term as well as an enthalpy defect formulation for steady and unsteady flamelet calculations are considered. Several model variants are introduced and discussed and the corresponding time scales for mixing, radiation and chemistry are analyzed. Based on the Lagrangian flamelet time and the enthalpy defect, both postprocessed from the CFD solution, flamelet calculations are carried out and detailed comparisons to the CFD simulation results are performed for the temperature and several species along the axis and in several radial slices. The results are finally used to evaluate the different approaches concerning their applicability and accuracy for use in coupled CFD-flamelet simulations.