【作者】 黄莉莉；

【导师】 胡隆华；

【作者基本信息】 中国科学技术大学 ， 安全科学与工程， 2018， 硕士

【摘要】 近年来,随着我国经济和科技的发展,以人为本的理念和环保意识的增强极大的改变了我国的能源结构。便于运输和清洁高效的气态能源正以不可阻挡的姿态走进人们的日常生活。然而由于各种各样的原因,超长燃气管线经常发生火灾、爆炸等灾难性质的事故,严重破坏了人们的生命和财产安全。一般来说,高压输送燃气的破裂管线根据其根部火源形状和较大的燃气喷出速度,可近似处理为线性湍流扩散射流火。在多处管道破裂时,因火焰间的相互作用而导致火焰被拉长,火焰方向改变,极有可能导致火旋风的形成,这种群发性火灾的火焰融合行为使得火灾更具破坏性和失控性。因而研究射流火焰相互作用的行为特点及其规律,对于防止射流火焰融合导致更大损失,具有重要意义。前人对多火焰相互作用行为特征进行了广泛的研究。然而,大量的研究工作主要探究的是轴对称火焰相互作用行为受燃料类型,扩散火焰类型,燃烧器数量及其分布和燃烧器间距的影响。而对于双线性火焰的相互作用行为的研究仍显著缺乏,尽管已有关于双线性层流扩散火焰相互作用的研究报道,但双线性浮力主控湍流扩散火焰相互作用机制还缺乏研究,由于湍流火焰的空气卷吸机理与层流扩散火焰存在显著差异,因此,有必要展开浮力主控湍流扩散双线性火焰相互作用的研究工作。本文通过实验的方法从火焰融合机制与火焰高度演化特征的角度切入来探究火焰相互作用行为。本实验采用两个完全一致的燃烧器,其内缝尺寸为2mm×142.5mm,燃烧器底部放置在高于水平地面0.4m的高度处。实验以丙烷为燃料,燃料出口速度范围0.23m/s-0.70m/s,在计算Fr和Gr后,核实本文火焰状态均为浮力主控湍流火焰。燃烧器间距的范围为0-1m。实验结果表明,随着燃烧器间距的增加,双火焰间的相互作用可将火焰形态划分为连续性融合、间歇性融合、无融合但有相互作用以及自由火焰状态,值得注意的是,当两个火焰发生融合时,其火焰高度很明显高于其相对应流量下的单一自由火焰高度。与此同时,火焰高度随着燃烧器间距的增大先减小后增大,并最终不断趋近于单一自由火焰高度,这是一个复杂的、非单调的变化过程,与前人在层流火焰中所观察到的规律截然不同,并且发现最小火焰高度恰巧出现在融合临界间距处,且该处的火焰高度低于单一自由火焰高度。本文将Kuwana等人根据层流扩散火焰推导出的融合临界间距模型拓展并应用到湍流扩散火焰中,构建了火焰融合概率模型和融合临界间距模型。发现了火焰融合概率模型可表达为三段函数的形式,融合临界间距模型表明融合临界间距正比于单一自由火焰高度,或者说与燃料出口速度呈2/3次方的关系。并提出了“有效”卷吸周长作为特征长度来量化双火焰的相互作用与空气卷吸行为特征,该“有效”卷吸周长包含了燃烧器的长、宽,火焰基部“扩展”和有效侧向卷吸特征长度,基于该“有效”卷吸周长,建立的火焰融合点高度模型和火焰高度模型。更多还原

【Abstract】 In recent years,with the development of our country’s economy and technology,an enhancing in People Oriented idea and environmental consciousness has changed the configuration of energy resource.Gaseous energy is stepping into our daily life as an irresistible gesture because of its convenience to transport as well as clean and efficiency.Nevertheless,for many reasons,many fires and explosions often occur along the long gas pipelines.Those disasters damage people’s life and property security greatly.Generally,fires caused by the breakage in the high pressure pipeline with a high blown-out velocity can be approximately taken as slot-burner diffusion jet fires.When pipelines are broken in many place,the flames can be stretched and deflected from the vertical due to the interaction between those flames.This may result in the formation of a fire whirlwind.The merging of group fires makes the fire more destructive and uncontrolled.Therefore,it is of great significance to study the interactions of jet fires to prevent flame merging from becoming a major cause of an uncontrolled fire.Numerous works have been conducted on the characteristics of multi-flame interactions.However,most of them mainly focused on the axisymmetric flames to investigate the effects of fuel type,diffusion-flame type,the number and distribution of burners,and the various burner pitch.While,the study on the interaction of slot-burner diffusion flames is relatively rarer.Although there have been reports on the interaction of slot-burner laminar diffusion flames,the interaction of slot-burner buoyant turbulent diffusion flames has not been studied yet.The air entrainment mechanism of a turbulent diffusion flame is essentially different from that of the laminar diffusion flames.So,it is necessary to study the interactions of multiple slot-burner buoyant turbulent diffusion flames.This dissertation carried out a series of experiments to explore flame merging mechanism and flame height evolution characteristics of two slot-burner buoyant turbulent diffusion flames.The experiment was conducted with two identical slot burners employed.The internal size of burners was 2mm × 142.5mm.The burners were located with its bottom being 0.4 m above the ground.Propane was used as the fuel and the fuel exit velocities varied from 0.23m/s to 0.70m/s.The flames here are buoyancy-controlled and turbulent based on the calculated Fr and Gr.Burner pitch ranges from 0 to 1 m.The experimental results show that with the increase of the burner pitch,the two flames show four merging behaviors:continuous merging zone,intermittent merging zone,non-merging with interaction and non-merging with no interaction.It is noted that when the two flames are merged,the flame height is much higher than that of a single free flame at the same fuel exit velocity.At the same time,the flame height decreases first,then increases and eventually approaches a single free flame height with increasing burner pitch.It is a complex,non-monotonic process,which is different from the observation in the laminar flame case.What’s more,it was found that the lowest flame height happens at nearly the critical burner pitch,and the flame height is lower than the single free flame height.This dissertation extended the model of critical burner pitch derived from laminar flame by Kuwana et al.to the turbulent diffusion flame.And also we developed correlations of the flame merging probability and the critical burner pitch.The flame merging probability can be expressed as a piecewise function into three regimes.The critical burner pitch is found to be scaled(proportional to)the flame height of a single free flame,or have a 2/3 power dependence on the fuel exit velocity.The flame merging height normalized by flame height is shown to be well fitted by an exponential function with normalized burner pitch."Effective" entrainment perimeter is proposed as a characteristic length to quantify air entrainment mechanism of the two interacting two slot-burner buoyant turbulent flames,including the burner width and length as well as the flame base "extension".The obtained flame heights at various burner pitches are shown to be well correlated based on the proposed effective" entrainment perimeter.更多还原