Trajectory correlations and mixing characterization for methane and hydrogen-rich jets in confined crossflow

Hydrogen enrichment of natural gas for fueling gas turbines introduces changes in fuel density, diffusivity and jet momentum that profoundly alter fuel–air mixing upstream of the flame, consequently altering flame behaviour. Despite the impact on flame stabilization, temperature distribution and thus NO x formation, the influence of hydrogen on jet-in-crossflow (JICF) mixing in confined, gas turbine relevant geometries remains poorly established. In this study, a non-reacting single circular jet in confined crossflow is investigated using high-fidelity Large Eddy Simulation (LES), with supplementary Reynolds-Averaged Navier–Stokes (RANS), for methane–hydrogen blends ranging from 0 to 100 vol% H 2 under constant thermal energy input. The LES results show a non-monotonic relationship between jet penetration and hydrogen content, with maximum penetration at X = 40 mm occurring at 80 vol% H 2 . This behaviour arises from competing effects of increasing jet momentum flux and decreasing fuel density. The Holdeman correlation underpredicts penetration for hydrogen-rich mixtures under the present conditions, which lie outside its validated momentum-flux range and configuration. Two new modified trajectory relationships were proposed based on the fits to present LES data, demonstrating improved agreement by prioritizing momentum-flux scaling while incorporating reduced density dependence. To characterize mixing quality, a time-dependent formulation of fuel–air unmixedness was introduced, extending conventional spatial-based metrics, to account for the temporal fluctuations resolved by LES. The results show a systematic reduction in unmixedness with increasing hydrogen content. This is driven primarily by enhanced turbulent kinetic energy rather than molecular diffusion alone. These findings provide new physical insight into hydrogen-enriched mixing in confined crossflows, identify the limitations of classical jet correlations for methane-hydrogen fuels, and offer improved correlations for hydrogen-enriched combustor design and development.