Numerical Simulation Study of Gas Stratification in Hydrogen-Enriched Natural Gas Pipelines

Hydrogen blending in natural gas pipelines facilitates renewable energy integration and cost-effective hydrogen transport. Due to hydrogen’s lower density and higher leakage potential compared to natural gas, understanding hydrogen concentration distribution is critical. This study employs ANSYS Fluent 2022 R1 with a realizable k-ε model to analyze flow dynamics of hydrogen–methane mixtures in horizontal and undulating pipelines. The effects of hydrogen blending ratios, pressure (3–8 MPa), and pipeline geometry were systematically investigated. Results indicate that in horizontal pipelines, hydrogen concentrations stabilize near initial values across pressure variations, with minimal deviation (maximum increase: 1.6%). In undulating pipelines, increased span length of elevated sections reduces maximum hydrogen concentration while maintaining proximity (maximum increase: 0.65%) to initial levels under constant pressure. Monitoring points exhibit concentration fluctuations with changing pipeline parameters, though no persistent stratification occurs. However, increasing the undulating height elevation difference leads to an increase in the maximum hydrogen concentration at the top of the pipeline, rising from 3.74% to 9.98%. The findings provide theoretical insights for safety assessments of hydrogen–natural gas co-transport and practical guidance for pipeline design optimization.