Simulation Experiment Design of Gas Mixing in Natural Gas-Hydrogen Blending Transportation Pipeline

Abstract Under the background of the "dual carbon" strategy, hydrogen has gained significant attention as a clean energy carrier, yet its high transportation costs constrain its development. Utilizing existing natural gas pipelines for hydrogen-blended natural gas transportation can substantially reduce costs. However, research on gas mixing behavior remains inadequate. To elucidate the gas mixing and migration mechanisms in hydrogen-blended natural gas pipelines and establish a virtual simulation experimental framework for engineering education, this study employs FLUENT to construct a 2D pipeline model (diameter: 0.5 m, length: 100 m). Using the standard k-\varepsilon turbulence model and a transient pressure-based solver, combined with the Wobbe index and combustion potential method, a safe hydrogen blending ratio range (0~23%) was determined. The effects of flow velocity, hydrogen blending ratio, transportation sequence, and pipe diameter on gas mixing development were systematically investigated. Results indicate: under low flow velocity (1 m/s), hydrogen tends to accumulate near the pipe top, while high flow velocity (15 m/s) induces transient concentration peaks due to the turbulent scouring effect; increasing the hydrogen blending ratio elevates overall hydrogen concentration, yet measured values fall below theoretical levels due to dilution by the initial gas source; transportation sequence has minimal impact on mixing length, while larger pipe diameters exacerbate radial concentration gradients. This simulation design visually demonstrates the dynamic mixing process, effectively developing students' competency in controlling key process parameters and solving complex engineering problems.