LARGE EDDY SIMULATION OF TURBULENT HYDROGEN FLAMES

Hydrogen is considered a promising energy carrier for low-carbon power generation, especially in gas turbine applications. However, its use introduces important challenges related to flame stability, strong differential diffusion effects, and increased nitrogen oxides (NOx) emissions. These issues are particularly critical in lean premixed conditions, which are commonly used to limit emissions but lead to complex turbulence-chemistry interactions. This dissertation investigates turbulent hydrogen combustion using large eddy simulation (LES) combined with advanced combustion modeling approaches. In particular, flamelet-based models and transported probability density function (PDF) methods based on the Eulerian stochastic fields (ESF) framework are employed to capture the interaction between turbulence and chemistry. The study focuses on both premixed and non-premixed hydrogen flames, using well documented experimental configurations for validation. The numerical results are assessed against available measurements, demonstrating the capability of the investigated modeling approaches to reproduce key features of the flow and flame structure. Special attention is given to the role of differential diffusion and flame stretch, with emphasis on tangential strain rate. The results show that these effects strongly influence flame structure, local reactivity, and stability, especially in lean premixed hydrogen–air mixtures. Their interaction leads to deviations from classical combustion behavior observed in hydrocarbon flames. Finally, the impact of tangential strain rate on NO formation is analyzed. The findings indicate that strain can significantly affect NO production by modifying temperature, radical concentrations, and reaction pathways. In particular, increasing tangential strain is shown to reduce NO emissions under certain conditions, suggesting a potential strategy for emission control in hydrogen combustion systems. Overall, this work provides a detailed assessment of LES-based combustion models for hydrogen flames and offers new insights into the coupled effects of strain and differential diffusion on flame behavior and pollutant formation.