管廊内泄漏口朝向对天然气管道泄漏扩散影响的模拟分析

Simulation analysis on influence of leakage opening orientation in utility tunnel on leakage and diffusion of natural gas pipeline

为掌握综合管廊内天然气输气管道泄漏口朝向对气体扩散的影响,使用FLUENT软件对4种不同朝向的泄漏口泄漏过程进行3维数值模拟,对比分析不同工况下气体浓度分布。结果表明:泄漏形成的射流产生强烈气体掺混,降低泄漏口附近气体浓度梯度;随着距泄露孔距离的增加,气体受惯性力作用减弱,并在浮力作用下抬升。管廊纵截面气体浓度场可分为泄漏口附近的均匀区和距离泄漏口较远的分层区。在均匀区内,探测器高度上气体质量分数纵向分布呈阶梯状;距泄漏口较远距离(大于20 m),泄漏口朝向对探测器高度上气体浓度纵向分布影响较小。基于稳态气体分布控制方程,提出气体在分层区内纵向分布关系式。当泄漏口刚好位于2探测器中央(最不利工况)时,泄漏孔朝向为X+(管道距离壁面较远侧)的泄漏气体在喷出后与空气接触时间长,产生涡量更大,使气体在管廊纵向上蔓延速度降低,探测器响应时间相对较长。

The three-dimensional numerical simulation on the leakage process of natural gas pipeline in the utility tunnel was conducted,and the gas concentration distribution of four different leakage opening orientations were compared.The results showed that the he jet formed by the leakage caused the strong gas mixing and reduced the gas concentration gradient near the leakage opening.As the distance from the leakage opening increased,the inertial force of gas weakened,and the gas was elevated under the action of buoyancy.Therefore,the gas concentration field on the longitudinal section of utility tunnel could be divided into a uniform area near the leakage opening and a layered area far away from the leakage opening.In the uniform area,the longitudinal distribution of the gas mass fraction at the height of detector was ladder-like.With farther distance from the leakage opening(about 20 m away),the leakage opening orientation had little influence on the longitudinal distribution of gas concentration at the height of detector.Based on the governing equation of gas distribution in the steady state,the relationship formula of the longitudinal distribution of gas in the layered area was proposed.When the leakage opening was just in the center of two detectors(the most unfavorable working condition),the leakage gas with the leakage opening orientation of X+(the pipe was farther away from the wall)would contact with the air for a long time after spraying out,and the vorticity was larger,so the spreading velocity of gas in the longitudinal direction of utility tunnel reduced,and the response time of detector was relatively longer.