Numerical Simulation of the Mixing Process for Natural Gas–Hydrogen Blends in a T-Junction Pipe

Abstract

Against the backdrop of energy decarbonization, utilizing existing natural gas pipelines for hydrogen blending represents a critical pathway for large-scale hydrogen transportation. This study employs numerical simulations using ANSYS Fluent, incorporating the species transport model and the Realizable k-ε turbulence model, to investigate the mixing process of hydrogen and methane within a T-junction pipeline. The effects of hydrogen blending ratio, flow velocity, injection position, and pipeline pressure on the mixing effectiveness are analyzed. The Coefficient of Variation (COV) is used to evaluate the mixing uniformity length. The results indicate that significant hydrogen stratification occurs initially in the pipeline, with diffusion and gradual homogenization occurring along the flow length. Within the hydrogen blending range of 5% to 20%, the difference in mixing length is limited. An increase in flow velocity extends the mixing distance due to reduced residence time. Injection from the bottom of the pipeline significantly shortens the mixing length (shortest at 9.1 m). Increasing the pressure to 0.6 MPa enhances mixing, but further pressure increases yield limited additional benefit.