Assessment of the Flamelet Generated Manifold method with preferential diffusion modelling for the prediction of partially premixed hydrogen flames

This study presents a systematic analysis of the capabilities of a flamelet model based on Flamelet Generated Manifolds (FGM) to reproduce preferential diffusion effects in partially premixed hydrogen flames. Detailed transport effects are accounted for by including a mixture-averaged transport model when building the flamelet database. This approach adds new terms to the transport equations of the controlling variables in the form of diffusive fluxes where the coefficients can be computed from the information contained in the manifold and saved in the flamelet database. The manifold is constructed from the solution of a set of premixed unstretched adiabatic one-dimensional flames with mixture-averaged transport for a range of mixture fraction within the flammability range. Special attention is given to the numerical aspects related to the construction of the chemical manifold to reduce the numerical error in evaluating the new terms derived from the preferential diffusion of certain species. Finally, a systematic application of the method to simulate laminar hydrogen flames in various canonical configurations is presented from premixed to stratified flames, including the case of a triple flames with different mixing lengths. The results demonstrate that the method describes accurately the flame structure and propagation velocities at a low cost, showing a remarkable agreement with the detailed chemistry solutions for flame structure and propagation velocity.