【作者】 姜孝海；

【导师】 范宝春； 叶经方；

【作者基本信息】 南京理工大学 ， 工程力学， 2004， 博士

【摘要】 泄爆是工业上广泛采用的爆炸防治手段之一，它是指通过泄爆口，将内部空间的高压已燃和未燃气体或粉尘导出到外部空间中，使内部压力迅速降低，以防止爆炸灾害。因泄爆过程的复杂性和某些不确定性，在一定的条件下，内压力虽降低了，而外流场可能出现很高的压力峰值，甚至产生所谓的二次爆炸，这对毗邻的建筑物、设备及人员的安全构成威胁。因此，研究泄爆外流场的动力学特征以及二次爆炸的产生机理，具有重要的意义。 本文利用自行设计的带导管的柱形泄爆装置，对不同泄爆条件(即泄爆压力、点火位置、泄爆面积和初始甲烷-空气预混气当量比)下向空气中泄爆的情形进行了实验，获得了内外流场的压力历史。并用YA-16高速阴影系统拍摄到了泄爆外流场清晰的时序阴影照片。而且，采用基于k-ε湍流模型和漩涡耗散湍流燃烧模型(“Eddy dissipation model”)的同位网格SIMPLE算法，对典型泄爆条件下的泄爆过程进行了数值模拟。根据计算结果和相关的计算流动技术(CFI)，绘制了计算阴影图。 基于实验结果、数值计算结果以及计算阴影图，本文对一般高压泄爆条件下，泄爆外流场的动力学特征(如射流火焰、湍流、漩涡以及可燃云团、波系特征等)进行了详细的系统的阐述，揭示了二次爆炸的产生机理。即在本文的泄爆条件下，泄爆后，首先产生的是引导激波，它由内外压差这个初始间断决定，因其传播速度较气流速度快，随波阵面的扩大而逐渐衰减为声波。随后，未燃气体从泄爆口泄出，并在外流场与空气混合形成可燃云团。由于高压(相对环境压力)气流在管口膨胀，形成欠膨胀射流。管口附近形成Prandtl—Meyer流稀释波低压区，而稀释波又在射流边界上反射并在轴线附近汇聚，形成压力相对较高的高压区，即悬吊激波高压区。这样，在火焰泄出前，外流场存在可燃云团、稀释波低压区和悬吊激波高压区，这些特征构成外流场的基本特征。当火焰从容器(低密度)进入导管(高密度)，受导管壁面剪切层等的作用，火焰失稳，在湍流的作用下加速向导管口推进，于管口附近达到极大值，以射流形式泄出。当射流火焰进入高压区时，且外流场处于合适的条件，如高压区的超压强度、可燃气体的密度及其覆盖的区域等足够大时，引起外部可燃气体的剧烈燃烧，从而使得外部压力迅速上升，以致产生二次爆炸。实验获得的阴影图和计算阴影图，形象的说明了泄爆后火焰、漩涡、引导激波以及随后产生的二次爆炸波的特征和变化发展过程。 文中还根据实验获得的不同泄爆条件下的外压力历史，分析了外部二次爆炸的影响因素，详细讨论了二次爆炸强度随泄爆条件的变化规律。即在其它泄爆条件不变时，而改变泄爆压力时，泄爆压力愈大，二次爆炸强度也愈大。同样，仅改变点火位置，而其它条件不变时，当泄爆压力较低时，二次爆炸强度随点火位置离泄爆口愈近，其值愈大；而当泄爆压力较大时，其变化规律与之相反。当其它条件不变而改变泄爆口障碍物的阻塞比时，二次爆炸强度随阻塞比的增大(即泄爆面积减小)而下降。当在改变初始甲烷-空气预混气的组分时，当量比小于1的情形，二次爆炸强度较当量比为1的情形小，而当量比大于1的情形，其值较大。更多还原

【Abstract】 Explosion relief venting is one of the methods applied widely in industries to avoid internal explosion. Namely, it can vent the high pressure unburnt and burnt gas mixture or dust to the outside space (generally the ambient air) through a device of low pressure resistance opening, when the explosion is in development and the overpressure exceeds a certain safe threshold(i.e. failure pressure). Because of the complexity and uncertainty in venting process, the inner overpressure could decrease, while the outer overpressure increases rapidly under some suitable conditions, and even external secondary explosions can occur. This gives potential explosion damage to neighboring structure or equipment or personnel in the vicinity. Therefore, it is necessary to investigate the dynamics of the vented external flow field and the mechanism of the secondary explosions during venting.In this paper, with a cylindrical vented vessel connected to a duct, the experiments on the venting to air under different venting conditions (failure pressure, vent area, equivalent ratio of the methane-air gas mixture and the location of ignition source) were performed and the pressure-time profiles of the external flow field were obtained. Moreover, some visualization tests of the external flow field were implemented by using YA-16 high-speed shadowgraph imaging system, and the clear sequential shadowgraph images were also obtained in tests. In addition, the venting process under the typical venting condition was simulated numerically, by using the colocated grids SIMPLE algorithm based on the k turbulent model and ’Eddy dissipation model’ turbulent combustion model. Furthermore, the computational shadowgraph images were plotted based on the numerical results and relevant computational flow imaging (CFI) methods.From the experimental and numerical results and computational shadowgraph images, the dynamic characteristics of the vented external flow field, namely,the jet flame, turbulence, vortex , flammable cloud and the structure of the pressure waves in the external flow field during venting, etc., were discussed systematically in detail. In the venting conditions covered in this paper, the leading shock wave generated due to the initial discontinuity of the pressure difference of the external and internal flow field, was firstly coming out of the vent. Then, the combustible gas rushed out and mixed with the oxygen of the air to form combustible cloud. The leading shock wave decayed to sound wave with its front expanding. The vented gas mixture jetted out under expansion for its higher pressure relative to ambient pressure, and the low pressure area near the exit was formed due to the rarefaction waves of the Prandtl-Meyer flow. And the high pressure area (also called ’Suspended shock wave’.) near the axis farther to the exit was also generated due to the convergence of those rarefaction waves reflected from theboundaries of the jet. The occurrence of the combustible cloud, low pressure area of the rarefaction waves and high pressure area of suspended shock were the basic characteristics in the external flow field before the flame spouted out. When the flame penetrated from the vessel(low density) into the duct(high density), it was accelerated due to instabilities occurring on its front and interaction of the shear layer of the duct wall, and its velocity near the exit was up to the maximum and then the jet flame rushed out. Under suitable conditions, for example suitable overpressure intensity and density in the high pressure area, and the area covered by the combustible in the external flow field, etc., the overpressure in the external flow field increased rapidly and even the secondary explosion occurred due to the violent combustion of the external combustible gas ignited by the jet flame. The characteristics of the flame, vortex, leading shock wave and secondary explosion generated later, were showed obviously from the clear sequential experimental shadowgraph images and computational shadowgraph images .In addition, the influenc更多还原