Stabilization of Hydrogen-enriched Jet Flames in a Crossflow

Flamelet based chemistry models provide a computationally efficient alternative to detailed finite-rate chemistry models for combustion modeling in practical applications. By solving one-dimensional flamelet equations, a flamelet database is built which is parameterised by a conserved scalar and a reactive scalar. The assumptions made during solving these equations restrict the validity of model to either a non-premixed mode (strained diffusion flamelet model) or premixed mode (unstrained premixed flamelet model) of combustion. In this study, we subject these two models to practical scenarios in which mixed combustion regime is likely to occur, aiming to enhance our comprehension of their effectiveness. A new strain-sensitive premixed model formulation is presented that involves solving a series of strained premixed flamelets, which are subsequently tabulated using a progress variable and hydroxyl radical. We use large-eddy simulations (LES) coupled with different flamelet models on a series of jet-incrossflow (JICF) experiments. To minimize uncertainties from subgrid-scale (SGS) models, sufficient grid resolution is provided in the reaction zones. In non-reacting scenarios, LES results demonstrate strong agreement with baseline experimental data. However, in reacting cases utilizing non-premixed tabulation, flame stabilization proves unsuccessful. Comparative analysis of experiments with unstrained and strain-sensitive flamelet LES models indicates a strong influence of strain on flame stabilization. Examination of instantaneous and temporally averaged field distributions for temperature, velocity, and flame structure highlights that the unstrained flamelet LES model tends to overestimate flame shape and location. Lifted flames in the jet shear layer predominantly exhibit a partially-premixed mode, with the strain-sensitive flamelet LES model capable of capturing the intricate physics between mixing and chemistry in highly strained regimes.