A study on the synergistic effects of hydrogen blending ratio and inlet configuration on mixing characteristics and energy efficiency in pipelines

Achieving China’s “Dual Carbon” strategic goals and facilitating a green transition of the energy structure necessitate the development of cost-effective hydrogen transportation. This study employs the Shear Stress Transport k–ω turbulence model to establish a three-dimensional numerical simulation of a tree-topology hydrogen-blended natural gas pipeline. It investigates the effects of hydrogen blending volume fraction (5%–25%) and the number of inlets (dual-pipe vs quadruple-pipe) on mixing characteristics, flow field structure, and system energy efficiency. The results reveal a significant coupling effect between the hydrogen blending ratio and the inlet configuration. At low to medium blending ratios (≤15%), the quadruple-pipe configuration enhances mixing uniformity, reduces the mixing distance, and generates stronger and more complex vortices by intensifying jet interactions. When the hydrogen blending ratio increases to 20% or higher, the dual-pipe structure is prone to forming hydrogen-enriched zones and velocity stratification due to localized jet concentration, whereas the quadruple-pipe structure demonstrates superior flow stability. As the blending ratio increases, the average flow velocity of the mixture rises, prolonging the flow field homogenization process. The quadruple-pipe structure mitigates this trend and maintains a more stable vorticity variation. At hydrogen blending ratios up to 20%, both inlet configurations contribute to system energy consumption control. However, under a high blending ratio of 25%, the quadruple-pipe structure achieves a maximum pressure drop reduction of 32.7%, offering significantly superior performance compared to the dual-pipe structure. These findings provide a theoretical basis and engineering reference for optimizing pipeline structures and enabling energy-efficient operation of hydrogen-blended natural gas pipelines.