环境温度对LNG泄漏扩散影响的数值模拟

环境温度导致的气云密度差和大气湍流变化是LNG泄漏扩散的主要影响因素,研究环境温度变化对LNG扩散规律的影响尤为重要。采用Fluent软件中组分输运和Realizable k-ε湍流模型,建立LNG地面泄漏气云扩散数值模型,探究环境温度对LNG泄漏扩散过程中甲烷体积分数的分布规律、气云密度、大气湍流强度的影响。结果表明:当环境温度较低时,LNG气云中各甲烷体积分数线出现"锯齿状"现象,造成甲烷爆炸下限(Low Flammability Limit,LFL)、1/2 LFL的水平扩散范围均增大;当环境温度较高时,甲烷LFL最远扩散距离较低温环境多115 m,造成甲烷1/2 LFL的水平顺风方向扩散距离增大;甲烷体积分数大于1/2 LFL的区域的大气湍流强度增幅则随温度升高而增加,而甲烷体积分数小于1/2 LFL的区域的大气湍流强度增幅随温度的升高而减小;在泄漏源周围100~200 m内,由于"逆温"所造成的大气湍流强度的增幅达0.79倍。研究结果可为LNG泄漏危害区域预测、安全储运、应急救援提供参考。

Numerical simulation on the effect of ambient temperature on leakage and diffusion of LNG

The difference of vapor cloud density and the variation of atmospheric turbulence caused by ambient temperature are the main factors influencing the leakage and diffusion of LNG.Hence,it is very necessary to study the influence of the variation of ambient temperature on the diffusion rules of LNG.With the component transport model and the Realizable k-εturbulence model in Fluent software,a numerical model of vapor diffusion caused by the surface leakage of LNG was established to explore the influence of ambient temperature on the volume fraction distribution of methane,vapor cloud density and atmospheric turbulence intensity in the process of LNG leakage and diffusion.The results show that under the low ambient temperature,the volume fraction lines of methane in the LNG vapor cloud is in the shape of"sawtooth",resulting in the increase of the horizontal diffusion range of the Low Flammability Limit(LFL)and 1/2 LFL of the methane,while under the high ambient temperature,the maximum range of diffusion of methane at LFL is 115 m farther than that under the low ambient temperature which leads to the increase of the diffusion range of methane at 1/2 LFL in the horizontal downwind direction.In addition,the increment of the turbulence intensity increases with the rise of the temperature in the area where the volume fraction of methane is greater than 1/2 LFL,while it decreases with the rise of temperature in the area where the volume fraction is less than 1/2 LFL.In the range of 100-200 m around the source of leakage,the increment of the turbulence intensity resulted by"temperature inversion"can be up to 0.79 times.The research results could provide references for prediction on leakage region,safety storage and transportation and emergency rescue of LNG.