A Comparative Computational Fluid Dynamics Study on Flamelet-Generated Manifold and Steady Laminar Flamelet Modeling for Turbulent Flames

摘要

The laminar flamelet model (LFM) (Peters, 1986, "Laminar Diffusion Flamelet Models in Non-Premixed Combustion," Prog. Energy Combust. Sci., 10, pp. 319-339; Peters, "Laminar Flamelet Concepts in Turbulent Combustion," Proc. Combust. Inst., 21, pp. 1231-1250) represents the turbulent flame brush using statistical averaging of laminar flamelets whose structure is not affected by turbulence. The chemical nonequilibrium effects considered in this model are due to local turbulent straining only. In contrast, the flamelet-generated manifold (FGM) (van Oijen and de Goey, 2000, "Modeling of Pre-mixed Laminar Flames Using Flamelet-Generated Manifolds," Combust. Sci. Technol., 161, pp. 113-137) model considers that the scalar evolution; the realized trajectories on the thermochemical manifold in a turbulent flame are approximated by the scalar evolution similar to that in a laminar flame. This model does not involve any assumption on flame structure. Therefore, it can be successfully used to model ignition, slow chemistry, and quenching effects far away from the equilibrium. In FGM, ID premixed flamelets are solved in reaction-progress space rather than physical space. In the present work, a systematic comparative study of the FGM model with the LFM for four different turbulent diffusion/premixed flames is presented. The first flame considered in this work is methane-air flame with dilution air at the downstream. The second and third flames considered are jet flames in a coaxial flow of hot combustion products from a lean premixed flame called Cabra lifted H_2 and CH_4 flames (Cabra, et al., 2002, "Simultaneous Laser Raman-Rayleigh-LIF Measurements and Numerical Modeling Results of a Lifted Turbulent H_2/N_2 Jet Flame in a Vitiated Coflow," Proc. Combust. Inst., 29(2), pp. 1881-1888; The fourth flame considered is a Sandia flame D (Barlow et al., 2005, "Piloted Methane/Air Jet Flames: Scalar Structure and Transport Effects," Combust. Flame, 143, pp. 433-449), a piloted methane-air jet flame. It is observed that the simulation results predicted by the FGM model are more physical and accurate compared to the LFM in all the flames presented in this work. The autoignition-controlled flame liftoff is also captured well in the cases of lifted flames using the FGM model.