Numerical simulation of deflagration-to-detonation transition in large confined volumes

A methodology for the computationally efficient CFD simulation of hydrogen-air explosions (including transition to detonation) in large volumes is presented. The model is validated by means of the largest ever conducted indoor DDT experiments in the RUT facility. A combination of models is proposed with a particular focus on the influence of flame-instabilities, especially of thermal-diffusive nature, which are crucial for very lean mixtures. Excellent agreement is achieved in terms of flame acceleration. The quality of DDT predictions itself depends on the underlying mechanism. Whereas DDT by shock-focusing is successfully simulated on under-resolved meshes, DDT by local explosions in the vicinity of the turbulent flame brush remains a challenge. Adaptive mesh refinement therefore emerges as a key technique to resolve more of the essential phenomena at reasonable computational costs affordable by industry. Finally, a generic case demonstrates the influence of mixture inhomogeneity, which can promote flame acceleration and ultimately DDT.     

Comments on explosion problems for hydrogen safety

The future widespread use of hydrogen as an energy carrier brings in safety issues that have to be addressed before public acceptance can be achieved. The prediction of the consequences of a major accident release of hydrogen into the atmosphere or the contamination of high-pressure hydrogen storage facilities by air entrainment requires a good knowledge of the explosion parameters of hydrogen–air mixtures. The present paper reviews and comments on the current knowledge of dynamic parameters of hydrogen detonation for hazard assessment. The major problem that remains to be resolved involves the understanding of the effect of turbulence on the cellular detonation structure, the propagation of high-speed deflagrations and the transition from deflagration to detonations. It is recommended that future research should be aimed towards experiments that permit the quantitative understanding of the mechanisms of high-speed turbulent combustion rather towards large-scale tests in complex geometries where minimal quantitative information of fundamental significance could be extracted. In spite of its wide flammability and sensitivity to ignition and detonation initiation, it is felt that hydrogen can be produced, stored and handled safely with the appropriate considerations in the design of the hydrogen facilities.     

Effect of ignition position on the run-up distance to DDT for hydrogen-air explosions

The method described in this paper enabled reliable and accurate positioning of an overdriven detonation by calculation of shock wave velocities (detonation and retonation) for hydrogen explosions in a closed 18 m long horizontal DN150 pipe. This enabled an empirical correlation between the ignition position and the run-up distance to DDT to be determined. It was shown that the initial ability of the flame to expand unobstructed and the piston-like effect of burnt gas expanding against the closed end of the tube contributed to initial flame acceleration and hence were able to affect the run-up distance to overdriven detonation. Flame speeds and rates of initial pressure rise were also used to explain how these two competing effects were able to produce a minimum in the run-up distance to DDT. The shortest run-up distance to DDT, relative to the ignition position, for this pipe and gas configuration was found when the ignition position was placed 5.6 pipe diameters (or 0.9 m) from the closed pipe end. The shortest run-up distance to DDT relative to the end of the pipe was recorded when the ignition source was placed 4.4 pipe diameters or 0.7 m from the pipe end.     

DDT and detonation propagation limits in an obstacle filled tube

Experiments with hydrogen–air and ethylene–air mixtures at atmospheric pressure were carried out in a 6.1 m long, 0.1 m diameter tube with different obstacle configurations and ignition types. Classical DDT experiments were performed with the first part of the tube filled with equally spaced 75 mm (44% area blockage ratio) orifice-plates. The DDT limits, defining the so-called quasi-detonation regime, where the wave propagates at a velocity above the speed of sound in the products, were found to be well correlated with d/λ = 1, where d is orifice-plate diameter and λ is the detonation cell size. The only exception was the rich ethylene limit where d/λ = 1.9 was found. In a second experiment detonation propagation limits were measured by transmitting a CJ detonation wave into an obstacle filled (same equally spaced 44% orifice plates) section of the tube. An oxy-acetylene driver promptly initiated a detonation wave at one end. In this experiment the quasi-detonation propagation limits were found to agree very well with the d/λ = 1 correlation. This indicates that the d/λ = 1 represents a propagation limit. In general, one can conclude that the classical DDT limits measured in an orifice-plate filled tube are governed by the wave propagation mechanism, independent of detonation initiation (DDT process) that can occur locally in the obstacles outside these limits. For rich mixtures, transmission of the quasi-detonation into the smooth tube resulted in CJ detonation wave. However, in a narrow range of mixtures on the lean side, the detonation failed to transmit in the smooth tube. This highlights the critical role that shock reflection plays in the propagation of quasi-detonation waves.     

喷淋塔内气液流场模拟

以实际建设中的燃煤机组为参考原型,使用数值模拟方法对于喷淋塔烟气流场进行了模拟分析.模拟结果表明,两入口塔入口不易积垢,流场均匀度也好于传统吸收塔.     

基于CFD分析的呼吸防护面具罩体设计

分析呼吸防护面具研究领域在呼吸阻力方面的研究情况,提出基于计算流体力学分析的呼吸防护面具罩体设计方案,在设计过程中添加以计算流体力学分析为手段的有限元模拟仿真模块。通过ANSYS产品ICEM CFD与CFX对设计模型进行网格划分与流体分析,根据仿真结果对初步设计的模型进行结构优化再设计。     

障碍物地形条件下重气泄漏扩散实验的CFD模拟验证

重气泄漏扩散是一种危害性较大的多发事故,而一旦在人口密集区域发生泄漏事故,周围居民将处境危险。重气泄漏后一般沿地面扩散,而地形条件是影响其扩散行为的重要因素。本文利用计算流体力学方法(CFD)对Thorney Island Trial026实验条件进行了数值模拟,考察障碍物对气体扩散的影响并与实验结果进行对比。结果表明,模拟结果与实验数据的吻合性较好,证明CFD软件能够较准确地模拟障碍物地形条件下的重气扩散过程。     

基于CFD的井喷失控喷射火温度场和辐射场模拟仿真

采用CFD方法研究了井喷失控喷射火,阐述了模拟仿真所需的定解条件,论述了模拟仿真采用的数值计算方法,通过模拟仿真得出了井喷失控喷射火温度场和热辐射场的分布规律.结论表明采用CFD方法研究井喷失控喷射火是切实可行的.     

基于CFD的毒气泄漏中毒定量评估

针对有关毒气急性中毒研究只能根据经验公式和接触限值划定危险区域进行定性评估的现状,提出结合毒气泄漏CFD数值模拟与中毒剂量反应模犁进行中毒定量评估的方法.通过CFD计算泄漏毒气的实时浓度场,根据浓度场和暴露时间确定人员暴露剂量,最后根据剂量反应模型确定人员死亡百分比.以某硫黄回收装置的硫化氢泄漏为例,建立CFD模型.设置距地面高1.5 m,与泄漏源水平距离分别为100 m、200 m、300 m、400 m、500 m的5个监测点作为工作人员的急性中毒地点.模拟分为构建初始风场、硫化氢泄漏及随风场扩散3个阶段,根据CFD求解得出的监测点的硫化氢实时浓度场并结合中毒剂量反应模型对监测点人员中毒死亡风险进行定量评估.研究表明,基于CFD的毒气泄漏中毒定量评估技术能对泄漏区域任意位置、任意时刻的人员中毒风险进行定耸评估,弥补了目前大多定性评价方法的不足.     

关于井喷H2S扩散数值模拟初步研究

井喷发生时,在复杂地形和气象条件下,用普通方法很难精确计算出场的时空分布.CFD(Computational Fluid Dynamics)方法虽然理论上能够计算,但是受限于目前的数学基础以及计算机计算能力的限制,CFD方法还很难在大范围地域条件下得到推广和应用.本文的目标就是如何在这些条件下采用合理的假设改进CFD算法,计算出井喷发生后的场的时空分布.在算例中,本文计算维多辛斯基曲线喷嘴射流的流场分布,并与实验值比较.结果证明,所采用的模型和计算方法的计算结果与实际情况基本相符,模型和计算方法可以适用井喷的数值模拟.     

井喷失控可燃性蒸气云形成数值模拟研究

利用计算流体力学方法(CFD)对井喷失控发生后天然气喷射流进行数值模拟研究,在有限元的基础上建立模型,采用紊流模型求解Navier-Stokes方程,计算井喷失控后任意时刻可燃气体浓度分布,考察不同风速对气体扩散的影响,最后得出井喷后易爆蒸气云稳定时间随风速变化规律.数值模拟计算结果与实验结果吻合较好,验证了紊流模型和数值算法的可靠性.该研究成果可对井喷失控后所形成的可燃性天然气易燃区域进行预测,有助于预防井场重大天然气着火、爆燃事故的发生.     

氨制冷系统压力管道安装及实验的要点

近年来,液氨管道事故的不断发生,引起了人们对氨制冷管道系统工程的高度重视.首先介绍了氨的性质,然后介绍了氨制冷管道安装及实验应该注意的一些要点,希望能对氨制冷工程的管道安装质量起到一些作用.