Abstract:

To evaluate the consequences of leakage accidents of the shallow subsea natural gas pipeline, this paper builds a calculation model of the shallow subsea pipeline leakage and diffusion process in light of computational fluid dynamics and multiphase flow theories for the strait?crossing section of a natural gas pipeline abroad. Three main factors, leakage aperture, leakage rate, and water flow velocity, are selected as condition variables to simulate the motion process of the gas?liquid two?phase flow under different conditions. The results show that underwater gas diffusion can be divided into three stages: the formation of gas masses above the leakage hole, the mushroom?like rise of gas masses, and the splitting of gas masses from large bubbles into small ones. Leakage aperture and leakage rate have a significant effect on the time when the underwater gas diffuses to the water surface. A larger leakage aperture and a higher leakage rate lead to a larger gas leakage amount, which further results in larger volumes of underwater air masses and ultimately a shorter time for them to reach the water surface. Water flow velocity has a significant effect on gas diffusion trajectory. As water flow velocity increases, the angle between the gas trajectory and the seabed decreases, and the diffusion distance along the ocean current direction becomes longer. This study can provide scientific guidance for emergency treatment of underwater natural gas pipeline leakage accidents.

Key words: Submarine pipeline, Gas leakage, Multiphase flow, Computational fluid dynamics

摘要：

为评价浅海海底天然气管道泄漏事故后果，根据计算流体力学与多相流动理论，针对国外某天然气管道海峡穿越段，建立浅海海底管道泄漏扩散过程的计算模型。将泄漏孔径、泄漏速率、水流速度3个主要影响因素作为条件变量，模拟不同情况下的气液两相运动过程。结果表明，水下气体扩散分为三个阶段，即泄漏口上方形成气团、气团呈蘑菇状上升、气团由大气泡分裂为小气泡；泄漏孔径和泄漏速率对水下气体扩散到水面的时间具有显著影响，泄漏孔径与泄漏速率越大，气体泄漏量越大；气体泄漏量越大，水下气团体积越大，到达水面的时间越短；水流速度显著影响气体的扩散轨迹，水流速度越大，气体运动轨迹与海底的夹角越小，沿海流方向扩散的距离越远。研究结果可为水下天然气管道泄漏事故应急处理提供一定的科学指导。

关键词: 海底管道, 气体泄漏, 多相流动, 计算流体力学