A high-efficiency strategy for blending hydrogen into high-pressure natural gas pipelines: Mechanistic modeling and numerical analysis

High-pressure hydrogen blending in natural gas pipelines is a key pathway for large-scale hydrogen utilization, while mixing uniformity directly affects pipeline safety and measurement accuracy and remains a critical issue to be addressed. This study proposes a novel blending strategy composed of a multi-hole injection element and a static disturbance element, and develops a high-fidelity numerical simulation framework based on Large Eddy Simulation (LES) to elucidate the mixing mechanisms under unsteady turbulent conditions. The predictive accuracy of the method was validated using a T-junction pipeline configuration. The effects of key parameters, including injection direction, injection hole number, hydrogen blending ratio, mainstream velocity, and operating pressure, on mixing performance and pressure drop were systematically investigated. The results show that: (1) the developed numerical method is able to accurately capture the mixing behavior of hydrogen and natural gas and the proposed blending method exhibited good performance in terms of mixing uniformity and energy efficiency under different conditions; (2) Under typical operating conditions, the use of counter-flow injection with 25 uniformly distributed holes increased the outlet mixing uniformity to over 99%, while maintaining the overall pressure drop below 10 kPa; (3) The mixing process was governed by a multistage cooperative mechanism of disturbance excitation, shear entrainment, and diffusive mixing, and the counter-flow injection generated high-speed shear layers and recirculation vortices that enhanced radial blending, while the downstream baffles induced forced perturbations, promoting rapid and uniform hydrogen diffusion over a short distance. The proposed LES solution procedure can provide a powerful tool for analyzing hydrogen-natural gas mixing, and the model proposed and results obtained could offer theoretical and engineering insights for the design and optimization of high-pressure hydrogen blending equipment.