Numerical and Experimental Study on Leakage Characteristics of Hydrogen-Blended Natural Gas during Pipeline Transport

A computational fluid dynamics (CFD) model was developed to investigate leakage characteristics of hydrogen-blended natural gas pipelines, and validated using a dedicated experimental platform with helium–nitrogen mixtures as safe surrogate gases. The effects of leakage path length-to-diameter ratio, hydrogen blending ratio, and leakage hole shape on leakage behavior were systematically analyzed. Results show that the leakage path length-to-diameter ratio strongly affects flow regime and resistance development, leading to actual leakage rates consistently lower than theoretical predictions. Hydrogen blending significantly intensifies leakage in terms of standard volumetric flow rate: at a 20% hydrogen blending ratio, the leakage rate increases by approximately 10.1–10.5% under low-pressure conditions, while pure hydrogen leakage results in an increase exceeding 184%, with the amplification effect becoming more pronounced as pressure rises. Below the critical pressure, both the leakage flow coefficient C hole and the discharge coefficient C d exhibit clear pressure dependence, limiting the applicability of conventional theoretical formulas. Based on these findings, a new parametric correlation incorporating pressure exponent, leakage area, and hydrogen blending ratio is proposed for rapid and accurate prediction of subcritical leakage rates, providing a practical tool for hydrogen-blended gas safety assessment.