Numerical Investigation of Premixed and Non-Premixed Hydrogen Flames Using Large-Eddy Simulations and Flamelet Models

Abstract A numerical investigation of premixed and non-premixed hydrogen flames is performed with the main aim of assessing the capability of large-eddy simulations and flamelet models to predict the main characteristics of the reactive field. Two different burners are investigated: (i) a premixed bluff body burner fuelled with a lean hydrogen-air mixture (ϕ = 0.4) and (ii) a non-premixed dual-swirl coaxial injector for which experiments show both anchored and lifted flames for the same global equivalence ratio (ϕg = 0.45). Simulations of the premixed burner are performed using the Flamelet Generated Manifold approach, whereas the two types of flames realized in the non-premixed burner are studied using the Steady Diffusion Flamelet and the Flamelet Generated Manifold. Numerical results are compared with the available experimental data for flow and flame characterization. As far as the velocity field is concerned, the investigated flamelet models have demonstrated capability to properly predict the location and magnitude of the velocity peaks and the shape of the inner recirculation zone in both the premixed and non-premixed cases. Moreover, the computational framework used in this study has demonstrated good accuracy in the prediction of the dynamic behavior of the flow. Regarding the structure of the flame, the models have shown a good capability to predict both the shape of the flame and the location of regions of high-intensity heat release rate. The present investigation offers a comprehensive assessment of large-eddy simulations and flamelet methods in the prediction of the behavior of two archetypes of hydrogen flames of industrial interest. The assessment shown here can provide support for the choice of methods to study cases with increased level of complexity.