APS—RS型高速相机在气相爆轰实验中的应用研究

基于气相燃烧转爆轰机理研究,探索利用APX-RS型高速数字相机测量氢氧混合气体在电火花点火后的火焰和前驱冲击波的变化历程,获得火焰加速以及冲击波的产生与成长过程的高速摄影图像;计算了不同位置的前驱冲击波参数和气体状态参数;分析了燃烧转爆轰机制。结果表明：APX—RS型高速相机可以成功地拍摄气相燃烧转爆轰过程,并获得氢氧混合气体燃烧转爆轰为局部爆炸机制。     

氢氧混合气体爆轰波的真实化学反应模型数值模拟

采用高精度的ENO格式和基于基元化学反应的真实化学反应模型求解氢氧混合气体一维爆轰波的精细结构。采用直接起爆方法得到稳定传播的爆轰波 ,计算的爆轰波阵面参数和实验相当符合。对爆轰波反应区化学反应的研究表明 ,参与反应的不同组分具有不同类型的变化特征。网格尺寸影响的研究表明 ,计算结果的精度随着网格尺寸的增加而增加 ,并能保持较好的收敛性。移动网格研究结果表明 ,网格运动速度和爆轰速度接近时 ,两者的相互作用对计算结果产生一定影响。     

二十年来的物理学——等离子体

二十年以前等离子体的研究在物理学中只占比较次要的地位。各式各样的等离子体现象没有被揭示出来。这个领域发源于本世纪初期对气体放电。即比较稠密的,稍微电离的等离子体区(其中主要效应是电离,受激、复合和其他原子碰撞过程)的研究。欧文·朗缪(frving Lang (?))发现等离子体静电振荡,并且认识到这是集体粒子运动的      

二十年来的物理学——等离子体

二十年以前,等离子体的研究在物理学中只占次要地位。各式各样的等离子体现象没有揭示出来。这个领域发源于本世纪初期,当时对气体放电,即对比较稠密的、稍微电离的等离子体区(其中主要效应是电离、受激、复合和其他原子碰撞过程)进行了研究。欧文·朗缪(Irving Langmuir)发现等离子体静电振荡,并且认识到:这是集体粒子运动的一个侧面,从而开创了近代等离子体物理。等离子体中的物理现象所以丰富多彩,并且使等离子体与普通流体那样不同,原因就在于这些产生电磁场,并与之相互作用的集体运动。在早期,天体物理和地球物理的研究也曾起过重要作用。爱德华·阿普尔顿(Edward Appleton)研究电离层时(在30年代),正确地描述了电磁波在等离子体中的传播(包括静磁场效应)。西德尼·查普曼(Sydney Chapman)和文森佐·费拉罗(Vincenzo Fer-     

关于等离子体诊断

Ⅰ.引言等离子体在一宽广的条件范围内工作。压力接近真空到几十巴;电流从几安到约10万安;流速从零到几千米/秒(流动可以呈现层流或湍流特性,可以强加速(象在收缩-扩张喷管中)或强减速(通过激波时))。由于这些多变的情况,温度可以是零点几电子伏到10电子伏量级,粒子密度和等离子体成分也在相应范围改变。非平衡效应在用作开关和加工方面都可起重要作用。对某一个领域(如开关)中给定的宽广应用范围,使用几种诊断方法是重      

热等离子体与能源

1.热等离子体及其应用概述等离子体按温度分类是一种较常用的分类方法:粒子温度范围为10~6-10~(8°)K的等离子体称为高温等离子体,如太阳、聚变等离子体等;粒子温度范围为3×10~2-10~(5°)K的等离子体称为低温等离子体,其中按重粒子温度(即气体温度)水平和热力学平衡的程度还可分为热等离子体与冷等离子体.所谓热等离子体是指重粒子温度在3×10~3-10~(5°)K范围,各种粒      

非平衡流模拟参数ρ∞L有效性的数值分析

在非平衡流相似律现有研究成果的基础上,通过对化学反应特征时间、具体流场区 域热化学状态、辐射输运方程的分析,并结合若干典型算例,讨论双体碰撞反应的非 平衡尺度效应模拟参数ρ∞L对高空高超声速飞行器全流场适用的条件.结果表明,当模拟参数ρ∞L值低于一定范围时, 在高超声速流场非平衡区中离解非平衡起主导作用,此时模拟参数 ρ∞L不仅对全流场的无量纲参数分布有效,而且对流场电离特性、模型气动热特性、分子光谱范围的驻 点辐射谱强度都是有效的.模拟参数ρ∞L的有效性与自由流速度、不同类物理量和流场不同区域均相关: 当自由流速度增加时, 对全场有效的ρ∞L要求ρ∞L 值减小;与无量纲压力、密度和温度相比, 对化学组元特别是离子组元分布有效的ρ∞L所要求的ρ∞L 值更小; 与模型头部区相比, 在身部区有效的ρ∞L所要求的ρ∞L值更小.     

基于非平衡多相模型的含铝炸药爆速研究

通过对爆轰反应区中铝粉压力、温度弛豫时间的计算,发现爆轰产物压力是平衡的,温度是不平衡 的。对传统CJ模型进行了改进,考虑爆轰产物的多相性和产物温度间的非平衡性,提出了一种新的计算含 铝炸药爆速的模型。采用该模型对几种含铝炸药的爆速进行了计算,并与已有的实验数据进行了对比,计算 结果优于传统CJ模型,与实验的误差在2%以内。     

非嵌入式多项式混沌法在爆轰产物JWL参数评估中的应用

介绍了非嵌入多项式混沌法的数学模型,给出了非嵌入式多项式混沌法进行不确定度量化的主要步骤。采用此方法研究了平面、散心爆轰问题数值模拟中, JWL模型参数R₁、R₂服从均匀分布的随机变量时所引起的爆轰过程计算结果的不确度性,着重分析了爆轰传播过程中压力与密度的统计特性。研究结果表明,非嵌入式多项式混沌法可以为模型输入参数不确定性的传播对输出结果响应量的影响建立一种有效不确定度评估方法,为使用JWL模型时选取参数提供参考。     

爆轰波在楔面上反射数值分析

应用基元反应模型和频散可控耗散格式(DCD)对氢氧爆轰波在楔面反射进行了数值模拟,计算中氢氧混合物的化学反应采用了8种组分20个反应方程式,在处理化学反应引起的刚性问题时采用了时间算子分裂的方法,模拟了爆轰波在楔面反射由马赫反射向规则反射转变的过程,得到了反射转变临界角,同时考虑了初始压力和组分的影响,并和实验及理论分析结果进行了比较,结果是令人满意的。     

The evolution of a detonation wave in a variable cross-sectional chamber

A two-dimensional numerical simulation has been performed to study the interaction of a gaseous detonation wave with obliquely inclined surfaces in a variable cross-sectional chamber. The weighted essentially non-oscillatory (WENO) numerical scheme with a relatively low resolution grid is employed. A detailed elementary chemical reaction model with 9 species and 19 elementary reactions is used for a stoichiometric oxy-hydrogen mixture diluted with argon. In this work, we study the effect of area expansion and contraction on the main/gross features of the detonation cellular structures in the presence of detonation reflection, diffraction and localized explosion. The result shows that there exists a transition region as the detonation wave propagates through the converging/diverging chamber. Within the transition region, the initial regular detonation cells become distorted and irregular before they re-obtain their regularity. While the ultimate regular cell size and the length of the transition region are strongly affected by the converging/diverging angle, the width/length ratio of the cells is fairly independent of it. A localized explosion near the wall is found as the detonation wave propagates in the diverging chamber.      

几种常用炸药的爆压与爆轰反应区精密测量

为了获得几种常用炸药的爆压和反应区宽度数据,采用激光干涉测试技术对TNT、PETN、RDX、HMX、TATB和CL-20炸药的稳态爆轰波界面粒子速度进行了测试,获得了高精度的界面粒子速度时程曲线,利用阻抗匹配公式计算得到了炸药的爆压。结果表明:PETN、RDX、HMX和CL-20等理想炸药的界面粒子速度曲线存在较明显的拐点,爆轰反应区较窄,反应时间为7~15 ns。TNT和TATB炸药由于存在碳凝聚慢反应过程,界面粒子速度曲线没有明显的拐点,爆轰反应时间分别为（100±15） ns和（255±20） ns。初步的不确定度分析表明,激光干涉法测试爆压的相对扩展不确定度为4.4%（包含因子k=2）。     

A multi-phase theory for the detonation of granular explosives containing an arbitrary number of solid components

Multiphase continuum models are commonly used to predict the shock, combustion and detonation behavior of granular energetic mixtures containing solid reactants and gaseous products. These models often include phase interaction terms that formally satisfy the strong form of the Second Law of Thermodynamics and provide flexibility in distributing dissipation between phases arising from non-equilibrium phenomena. This work presents a thermodynamically compatible constitutive theory for reactive systems containing an arbitrary number of solid components. The theory represents a rigorous extension of the two-phase theory formulated by Bdzil et al., based on the well-studied Baer–Nunziato model. Forms of the gas–solid and solid–solid interphase sources suggested by general reactions of type A → B are considered, where the combustion processes discussed in Bdzil et al. are treated as a special case. The model energetics are augmented by supplemental evolutionary equations that track local changes in phase temperatures due to dissipative and transport processes allowing for the identification of dominant energetic processes. This capability provides a mean to identify system parameters (e.g., metal particle size and mass fraction in metalized energetic mixtures) which optimize performance metrics. Detonation predictions are given for mixtures of granular HMX and aluminum to demonstrate model features and to highlight the effect of aluminum particle self-heating by oxidation on detonation. Predicted spatial profiles for mechanical fields, and the heating contributions from individual dissipative processes, illustrate how aluminum particle size can affect the coupling of oxidative heating to the explosive reaction zone.     

One-dimensional flows of a nonequilibrium plasma with variable degree of ionization in the absence of currents

The one-dimensional flows of an inviscid plasma not in thermal equilibrium and with a variable degree of ionization are investigated in the absence of currents. A criterion showing when the ordinary equations of gasdynamics may be used to describe these flows is given. An expression is found for the velocity of sound in such a plasma. Under certain conditions it passes into Newton's formula for isothermal sound. The condition fulfilled in the critical cross section of the channel is found. It is established that the flow of a weakly ionized plasma occurs at constant electron temperature. A detailed investigation is made of the possible types of flow in a cylindrical channel.A criterion is given which shows when the model of a plasma in thermal equilibrium may be applied, and also relationships which permit complete calculation of the flow of such a plasma in a channel of variable cross section.Generally speaking, the flow of a plasma with no currents present differs from the flow of a nonionized gas. This difference is related to the processes of ionization and recombination taking place in the plasma. The electrons usually play the main part in these processes, and so the average energies (temperatures) of electrons and heavy particles (atoms and ions) may differ. If the inelastic collision frequency in the plasma is small compared with the elastic collision frequency, then the temperature difference between the electron component and the heavy component of the plasma may be considerable. The simplest cases of one-dimensional plasma flows are considered with account for ionization and recombination processes and in the absence of thermal equilibrium among the components.The author is grateful to M. N, Kogan for discussing the paper.     

Some observations of detonation propagation through a gas containing dust particles in suspension

An experimental study of the influence of low concentration particle suspensions on the propagation of detonation waves in a combustible gaseous mixture is presented. In all cases the particles have an effect on the propagation of the detonation but at certain concentrations, both with inert and combustible particles, a zone of reduced pressure is observed following the detonation front. At the end of this zone there is a sharp pressure increase, which, in some instances, resembles a second shock or detonation front. The paper considers the possible origins of this second pressure rise.R.O. Carvel, Present address: Department of Civil and Offshore Engineering, Heriot-Watt University, Edinburgh EH14 4AS, UK     

Mechanism of deflagration-to-detonation transitions above repeated obstacles

Experiments are carried out to investigate the mechanism of the deflagration-to-detonation transition (DDT). Because, this mechanism has relevance to safety issues in industries, where combustible premixed gases are in general use. A stoichiometric gas of oxygen and hydrogen (oxy-hydrogen) is ignited in a tube, repeated obstacles are installed, and the DDT behaviours are visualized using a high-speed video camera. The pitch and height of the repeated obstacles and the initial pressure of the oxy-hydrogen premixed gas are varied in an attempt to obtain the optimum conditions that cause DDT a short distance from the ignition source. The experiments identified DDT as being essentially caused by one of the following mechanisms: (1) A deflagration wave is accelerated in terms of a vortex, which is generated behind the obstacle, and the flame acceleration induces a secondary shock wave. Eventually, the shock–flame interaction ahead of the obstacle causes DDT via a very strong local explosion. (2) Each shock wave generated by relatively weak local explosions between the obstacles is not sufficient to cause DDT directly, but DDT results from an accumulation of shock waves. The detonation induction distance is also examined, taking into account the physical and chemical parameters of the obstacles and the oxy-hydrogen premixed gas.     

An empirical model for the ignition of explosively dispersed aluminum particle clouds

An empirical model for the ignition of aluminum particle clouds is developed and applied to the study of particle ignition and combustion behavior resulting from explosive blast waves. This model incorporates both particle ignition time delay as well as cloud concentration effects on ignition. The total mass of aluminum that burns is found to depend on the model, with shorter ignition delay times resulting in increased burning of the cloud. After the Al particles ignite, a competition for oxidizer between the booster detonation products and Al ensues. A new mass-averaged ignition parameter is defined and is observed to serve as a useful parameter to compare cloud ignition behavior. Investigation of this variable reveals that both peak ignition as well as the time required to attain peak ignition, are sensitive to the model parameters. The peak degree of dissociation in the fireball is about 19 % and the associated energy can play a significant role on the dynamics of the problem. The peak degree of ionization is about 2.9 % and the energy associated with this is much lower than the other controlling factors. Overall, this study demonstrates that the new ignition model developed captures effects not included in other combustion models for the investigation of shock-induced ignition of aluminum particle clouds.     

Shock-induced Near-wall Two-phase Flow Structure Over a Micron-sized Particles Bed

The present paper studies numerical modelling of near-wall two-phase flows induced by a normal shock wave moving at a constant speed, over a micron-sized particles bed. In this two-fluid model, the possibility of particle trajectory intersection is considered and a full Lagrangian formulation of the dispersed phase is introduced. The finiteness of the Reynolds and Mach numbers of the flow around a particle as well as the fineness of the particle sizes are taken into account in describing the interactions between the carrier- and dispersed-phases. For the small mass-loading ratio case, the numerical simulation of flow structure of the two phases is implemented and the profiles of the particle number density are obtained under the constant-flux condition on the wall. The effects of the shock Mach number and the particle size and material density on particle entrainment motion are discussed in detail. The obtained results indicate that interphase non-equilibrium in the velocity and temperature is a common feature for this type of flows and a local particle accumulation zone may form near the envelope of the particle trajectory family.     

Detonation waves in trinitrotoluene

Fabry-Perot, ORVIS, and VISAR laser interferometry are used to obtain nanosecond time resolved particle velocity histories of the free surfaces of copper and tantalum discs accelerated by detonating trinitrotoluene (TNT) charges and of the interfaces between TNT detonation products and lithium fluoride crystals. TNT detonation reaction zone profiles are measured for self-sustaining detonation and piston supported overdriven (supracompressed) waves. The experimental records are compared to particle velocity histories calculated using very finely zoned meshes of the exact dimensions with the DYNA2D hydrodynamic code. The Ignition and Growth reactive flow model, which is based on the Zeldovich-von Neumann-D?ring (ZND) theory of detonation, yields excellent agreement with the experimental records for TNT using an unreacted von Neumann spike pressure of 25 GPa, a reaction rate law which releases 90% of the chemical energy within 80 ns and the remaining 10% over an additional 200 ns, and a reaction product equation of state fit to cylinder test data assuming a Chapman-Jouguet pressure of 19 GPa. The late time energy release is attributed to diffusion controlled solid carbon particle formation. Received 26 July 1997 / Accepted 29 December 1997     

气相爆轰波胞格尺度与点火延迟时间关系研究

讨论点火延迟时间和爆轰波胞格尺度的内在关系,将点火延迟时间作为特征参量来模拟胞格尺度. 分别对两个总包单步化学反应模型和一个基元反应模型的点火延迟时间进行了数值模拟研究. 对于满足当量比的氢气/空气混合气体,分析了不同初始压力下点火延迟时间随初始温度的变化关系. 研究表明:总包单步反应模型的点火延迟时间不随压力变化,且与初始温度呈线性关系. 基元反应模型的点火延迟时间随压力变化,而且存在理论上的S 型曲线,但是在拐点区域和低温区域与CHEMKIN 计算的结果相差1~3 个量级. 现有模型模拟的胞格尺度普遍偏小,其相应的点火延迟时间也偏小,胞格尺度与点火延迟时间具有正相关性. 入射激波后的气体的点火延迟时间与三波点的运动周期一致,是定量化模拟胞格的关键因素.