Abstract: Urban gas pipeline network is mostly laid underground, which brings difficulties to detecting small leakage.After the leakage,it is prone to poisonous accidents such as poisoning, fire, explosion, etc., which brings hidden dangers to urban public safety.This paper sets up a calculation model for two backfilling methods of layered soil and non layered soil in pipe network,and different physical convection diffusion models are established for different laws of gas diffusion in soil and atmosphere environment.Based on the unsteady leakage model and the CFD software, the paper analysis the buried duffusion separately and analysis the atmospheric diffusion coupling soil and atmosphere.And the study about the effect of back filled soil on the diffusion of gas in soil and atmosphere.The results show that:low⁃ and medium⁃ concentration gas will delay diffusion and produce inflection point through stratified interface. The diffusion rate will increase after the layered interface, and the diffusion rate of gas in the layered soil will be high when the leakage time is greater than 100 s.The atmospheric diffusion rate of methane under stratified soil is not much different between the upwind side wind and the downwind directions. The longitudinal 100 s diffusion rate is larger than that one of the non stratified soil, and the larger the inertial resistance coefficient is, the faster the diffusion is.

Key words: Stratified soil, Unstable leakage, Diffusion, Couple, Simulation

摘要： 城市燃气管网多为埋地敷设，给探测微小泄漏带来了困难，而燃气泄漏后容易发生中毒、火灾、爆炸等恶性事故，给城市公共安全带来隐患。针对管网分层筑土和不分层筑土两种回填方式建立计算模型，并针对土壤和大气环境中燃气扩散规律的不同建立不同的物理对流扩散模型；基于非稳态泄漏模型，以CFD软件为基础，分析燃气在土壤中扩散时进行单独求解，分析燃气在大气中扩散时进行土壤和大气耦合求解。研究回填筑土方式对燃气在土壤和大气中扩散规律的影响。结果表明，低、中浓度燃气通过分层交界面时会发生延迟扩散，并产生拐点，通过分层交界面后扩散速率加快，泄漏时间大于100 s时燃气在分层筑土中的扩散速率均高于不分层筑土中的扩散速率；分层筑土时，CH4在大气中迎风横向和顺风向的扩散速率相差不多，泄漏100 s后纵向扩散速率大于不分层筑土时的纵向扩散速率，且惯性阻力系数越大，扩散越快。

关键词: 分层筑土, 非稳态泄漏, 扩散, 耦合, 模拟