起伏天然气掺氢管道气体静置分层过程数值研究

天然气管道掺氢输送被认为是当下清洁、经济转运氢能的方式之一。利用计算流体力学方法，研究了均匀掺入不同体积分数氢气的起伏天然气管道停输后气体静止分层的过程，重点分析了起伏高差对静置分层发展历程及稳定后氢气最高体积分数的影响。结果表明，倾斜管内气体剪切作用尤为明显，气体流动可分为4个阶段：剪切启动与增强阶段、剪切起旋与衰减阶段、旋涡消亡与流动平整阶段、流动减速与垂向分层阶段。气体流动的强弱直接决定了管内体积分数的变化历程。起伏高差和管道长度同时增加的条件下，气流剪切作用加剧，静置分层达到稳定所需的时间更长。因而，需依据氢气风险浓度确定停输检修的安全窗口期。

Numerical Investigation of the Natural Gas-hydrogen Mixture Stratification Process in an Undulating Pipeline

The transportation of nature gas mixed with a specific volume of hydrogen is considered to be one of the green and economical ways to transmit hydrogen. In this research, a series of numerical simulations is conducted to capture the stratification process of natural gas mixed with different volume fractions of hydrogen in an undulating pipeline after the shutdown. The effects of the height of undulating pipeline on the process of gas stratification and the maximum hydrogen concentration are examined. An obvious shear effect between gas flows is observed in the inclined tubes of such undulating pipeline. The gas flow in the pipeline could be classified into four stages:initiation and enhancement stage of gas shear effect, vortex formation and shear attenuation stage, vortex extinction and flow stabilization stage, and flow deceleration and vertical stratification stage. The variation of gas concentration depends on the strength of gas flow. The increase of pipeline height or total volume intensifies the shear effect of gas flow, resulting in a longer consuming time for the stable stratification. Therefore, a safety window period for shutdown maintenance is important to be determined according to the risk value of hydrogen concentration.