风速对LNG泄漏扩散过程影响的数值模拟

为研究环境风速对液化天然气(LNG)泄漏扩散过程的影响,采用Fluent建立LNG连续泄漏计算流体力学模型,开展不同风速下LNG泄漏扩散过程的数值模拟研究。结果表明,LNG泄漏扩散分为扩散初期、扩散中期、扩散后期3个阶段,扩散过程中LNG从低温重气逐渐转变成轻质气体。环境风速对气云的扩散主要体现在:低于5级风时,云团以两侧卷吸为主,气云表现为"叶状分叉"、中间低两端高,此时气云横风向扩散较快,甲烷扩散距离与冻伤距离随风速增大而增大;而高于5级风时,云团以顶部卷吸为主,气云表现为云团坍塌、中间高两端低,此时气云垂直风向扩散较快,甲烷扩散距离与冻伤距离随风速增大而减小。初步建立了LNG蒸气云爆炸风险范围与冻伤区域和泄漏时间、环境风速的函数关系,可为爆炸风险区域和低温冻伤区域的预测提供理论支撑。

Numerical simulation of the effect of wind speed on LNG leakage and the diffusion process

To simulate the leak diffusion process of the LNG( short for liquefied natural gas) under the 5 wind speeds in response to the needs of the fast development of the liquefied natural gas industry in recent years,the paper would like to bring about lots of gas-use application safety problems in response to the low temperature flammability of the liquefied natural gas vapor. To expose the influence of the ambient wind speed on the leakage and diffusion of the liquefied natural gas( LNG),the paper has adopted the realizable κ-ε turbulence model and the component transport model in the Fluent software and found the following results: the LNG leakage and diffusion can be divided into 3 stages: the initial stage,the intermediate stage and the later consequential stage. During the LNG diffusion,the LNG has been gradually changing from heavy gas of the low temperature to the light gaseous state. And,in the diffusion of the LNG,the wind-moving speed tends to change the cloud shape and influence the diffusion distance of methane. However,when the wind speed is getting lower than 8 m/s,the cloud would be mainly entrained to the both sides,which makes the cloud featured by"the foliage bifurcation"with 2 ends being high and the middle being low. And in the changing process,the transverse diffusion of the gas cloud goes faster,whereas the distance between the methane diffusion and the frost-bite is turning to expand with the increase of the wind speed. And,eventually,the methane diffusion distance under the wind speed of 8 m/s would be getting to 561 m,which should be 80% higher than that of the frost-bite under the wind speed of 2 m/s. And,then,when the wind speed is getting to be greater than 8 m/s,the cloud of the vertical wind direction would be mainly entrained at the top.Thus,the cloud would be collapsed with the middle becoming higher and the two ends getting lower. At this juncture,the vertical direction wind of the cloud would diffuse faster,whereas the distance between the methane diffusion and the frostbite would become less and less with the increase of the wind speed up to the methane diffusion distance of 93 m till the wind speed gets to10 m/s,which turns to become 85% less than that under 8 m/s. And,thus,the functional relationship between LNG vapor cloud explosion risk range and the frostbite area can be established,with the leakage time and the ambient wind speed being preliminarily calculated and fixed up,which can provide a reasonable theoretical support for the prediction of the explosion risk area and cryogenic frostbite area.