An Extended Artificially Thickened Flame Model for Turbulent Hydrogen and Hydrogen-Enriched Flames With Intrinsic Instabilities Under Gas Turbine Relevant Conditions

Abstract

Hydrogen and hydrogen blends with ammonia or natural gas are cornerstones in the transition to future environmentally friendly energy systems, such as gas turbines and aero-engines. However, hydrogen's unique characteristics lead to intrinsic flame instabilities, resulting in an up to sixfold increase in turbulent flame speeds under gas turbine-relevant conditions compared to flames without instabilities. These effects are not captured by current combustion models, presenting a major barrier for computational fluid dynamics (CFD) simulations. This study addresses these limitations by developing an extension to the widely used artificially thickened flame (ATF) model, validating it for wide operating conditions and applying it to turbulent configurations. To this extent, over 200 direct numerical simulations (DNS) of laminar planar flames are analyzed, unraveling the characteristics of the enhanced flame speed. The subsequently developed model is validated across comprehensive variations in pressure (1 atm-20 atm), temperature (300 K-700 K), equivalence ratios (φ=0.4-1.0), and fuel compositions (pure H2, precracked ammonia (NH3/H2/N2) and hydrogen natural gas blends (CH4/H2)) to ensure the model's applicability for technically relevant operating conditions. Additionally, the model is transferred to turbulent conditions using Large Eddy Simulations. For model validation, multiple high-fidelity DNS of turbulent jet flames at various conditions are performed. The advanced model shows excellent agreement in a laminar configuration and significant improvements in predicting turbulent flame speeds of the turbulent jet flames compared to the state-of-the-art model. By enhancing the widely used ATF model to account for hydrogen characteristics, this study supports the further development of efficient and environmentally friendly hydrogen-powered energy systems.