Modelling detonation of heterogeneous explosives with embedded inert particles using detonation shock dynamics: Normal and divergent propagation in regular and simplified microstructure

This paper discusses the mathematical formulation of Detonation Shock Dynamics (DSD) regarding a detonation shock wave passing over a series of inert spherical particles embedded in a high-explosive material. DSD provides an efficient method for studying detonation front propagation in such materials without the necessity of simulating the combustion equations for the entire system. We derive a series of partial differential equations in a cylindrical coordinate system and a moving shock-attached coordinate system which describes the propagation of detonation about a single particle, where the detonation obeys a linear shock normal velocity-curvature (D_n–κ) DSD relation. We solve these equations numerically and observe the short-term and long-term behaviour of the detonation shock wave as it passes over the particles. We discuss the shape of the perturbed shock wave and demonstrate the periodic and convergent behaviour obtained when detonation passes over a regular, periodic array of inert spherical particles.     

Experimental investigation and numerical validation of explosion suppression by inert particles in large-scale duct

A large-scale duct with an explosion suppressor was designed to investigate experimentally the explosion suppression by inert particles for a CH₄/O₂/N₂ mixture. The duct is 25 m long and has an internal diameter of 700 mm. Pressure and flame signals were recorded some distance away from ignitor in the duct. Pressure tracking lines of the shock front for the different inert particle cloud densities and the inert particle diameters were made. The measured results indicate that the shock front is decoupled from the flame front in the inert particle cloud, which leads to a suppression of explosion. Also, the experiments suggest that increasing the inert particle cloud density or decreasing the inert particle diameter can enhance the ability to suppress explosion. For the purpose of validation, a two-dimensional numerical model coupled with the element chemical reaction mechanism for the simulations of the CH₄/O₂/N₂ mixture explosion suppression by the inert particles has been developed. This model makes use of the second-order TVD scheme and the MacCormack scheme to calculate gas-phase and particle-phase equations, respectively. The Strang splitting technique is used to treat the stiffness due to the coupling of the governing equations, while the implicit Gear algorithm is used to treat the stiffness due to the chemical reactions. The effect of inert particle cloud density on explosion suppression was investigated using the model. The calculated results indicate that the accumulation of inert particles slows the propagation of the gas-phase shock front and results in explosion suppression. With increased inert particle cloud density, the explosion suppression is more prominent. The calculated results show a qualitative agreement with the measured results in the large-scale duct experiment.     

悬浮RDX炸药粉尘爆轰的数值模拟

用两相流模型对悬浮RDX炸药粉尘爆轰波进行了数值模拟。RDX炸药颗粒在爆轰波阵面后的高温高速气流中加速并升温,颗粒表面发生熔化。参考液滴在高速气流作用下剥离的效应,假设炸药熔化部分在高速气流的作用下发生剥离,破碎成极小的颗粒,瞬时发生分解反应,释放出能量支持爆轰波传播。数值模拟了在不同粒径和浓度的悬浮RDX炸药粉尘中爆轰波的发展与传播过程,得到了爆轰波流场中气-固两相的物理量分布,并确定了爆轰波参数。在较低的RDX粉尘浓度条件下,爆轰波阵面压力的峰值曲线出现振荡。当RDX粉尘浓度在80~150 g/m3时,数值模拟得到的爆轰波阵面压力峰值曲线的振荡是规则的;当RDX粉尘浓度为70 g/m3时,爆轰波阵面压力峰值曲线出现不规则振荡。     

CE/SE方法数值模拟炸药粉尘爆轰

采用CE/SE方法数值模拟悬浮在空气中的RDX炸药粉尘的两相爆轰过程.炸药颗粒在爆轰波阵面后的高温高速气流中加速并升温,释放能量支持爆轰波传播.数值模拟爆轰波管中的粉尘爆轰,得到爆轰波流场中的物理量分布,确定爆轰参数,数值结果与文献符合较好.数值模拟复杂通道中的炸药粉尘爆轰,预测了爆轰波的发展和传播过程以及爆轰波后的流场演化.数值结果表明CE/SE方法能成功模拟气体-固体两相爆轰,为粉尘爆轰的研究提供了新的数值预测手段.     

Turbulent flame propagation limits of polymethylmethacrylate particle cloud–ammonia–air co-combustion

Ammonia is a highly promising energy carrier for achieving a carbon-neutral society. The co-combustion of solid particle clouds–ammonia, in particular, is considered an efficient and feasible method of reducing carbon dioxide emissions. Understanding turbulent flame stabilization and extinguishment processes during the two-phase hybrid-mixture co-combustion of solid particle clouds–ammonia is essential for the co-combustion technology to be used in combustors. To the best of our knowledge, this is the first study to describe the turbulent flame propagation limits and associated mechanism on the co-combustion of solid particle clouds–ammonia–air. Turbulent flame propagation experiments on silica particle clouds–ammonia–air mixing combustion and polymethylmethacrylate (PMMA) particle cloud–ammonia–air co-combustion were conducted in this work using a novel fan-stirred constant-volume vessel to clarify the turbulent flame propagation limits and associate mechanism of solid particle cloud–ammonia–air co-combustion. Results showed that adding inert silica particles contracted the turbulent flame propagation limits of premixed ammonia–air mixtures. However, adding PMMA particles expanded and then contracted the turbulent flame propagation limits of a premixed ammonia–air mixture as the ammonia equivalence ratio increased from lean to rich. In the solid particle cloud–ammonia–air co-combustion, reactive particles induce two types of effects on the turbulent flame propagation limits of premixed ammonia–air mixtures: The local equivalence ratio increment effect is caused by adding volatile matter from preheated particles in the preheat zone of the flame front, and the heat sink negative effect is induced by the unburned particles.     

Particle acceleration and magnetic field amplification in supernova shells: A nonlinear Monte Carlo model

A nonlinear model of particle spectra and nonadiabatic magnetic field amplification in supernova shells is presented. The effect super-diffusive particle propagation in the vicinity of a shock wave has on the spectra of accelerated particles and magnetic field fluctuations is studied in a Monte Carlo simulation.     

Molecular dynamics simulation of plastic effects upon spalling

The molecular dynamics method is applied to simulate spalling during the plane shock interaction between plates. The effect of lattice defects in a material on the propagation of a shock wave and the process of spalling is studied. The plastic effects are described using a model of imperfect particle packing with defects (vacancies). The model proposed can describe the separation of the shock-wave front into an elastic precursor and a plastic front and give velocity profiles for the free target surface close to the experimental profiles.     

Detonation of explosives containing heavy inert particles

The physical and mathematical aspects of the theory of a detonation wave containing heavy inert particles are considered. The detonation wave intensity and structure are determined by the relaxation of velocities of both the reactive explosive and the inert admixture. The generalized Jouguet condition is formulated for the velocity of a self-sustained detonation wave. The results of analytical treatment and the model numerical solutions of the problem of the detonation wave velocity selection and the wave structure determination are presented as a function of the ratio of the characteristic times of the heat evolution and the two-component flow velocity relaxation. A limiting case of the fast particle drag is represented by the shock wave structure determined by relaxation of the two-component flow velocity.     

Effects of the diffusive acceleration of particles by shock waves in the primordial matter of the solar system

The effects of the shock wave diffusive acceleration of particles are considered in the case of formation of isotopic relations of the anomalous Xe-HL component of xenon in relic grains of nanodiamonds in chondrites. It is shown that this component could be formed and captured simultaneously with the nanodiamond synthesis in the conditions of the explosive shock wave propagation from supernova outbursts. The specificity of isotopic composition of Xe-HL is due to the high hardness of the spectrum of nuclear-active particles at the shock wave front and its enrichment with heavy isotopes. The spallogenic nature of both the anomalous and normal components of xenon is ascertained, and the role of the subsequent evolutionary processes in the change of their isotopic systems is shown. Experimental evidence of the formation of the power law spectrum of particles with the spectral index γ ∼ 1 by the supersonic turbulence during the carbon-detonation supernova SnIa explosion is obtained; this perhaps opens new perspectives in studying the problem of the origin of cosmic rays. It is shown that at the stage of free expansion of the explosive shock wave, the degree of compression of the matter at the wave front was σ = 31 (the corresponding Mach number M ∼ 97); this led to a 31-fold increase of the magnetic field as well as of the maximum energy of accelerated particles, so that even the energy of protons reached ∼ 3 × 10¹⁵ eV, i.e., the “knee” region.     

燃料抛撒成雾及其燃烧爆炸的光滑离散颗粒流体动力学方法数值模拟研究

燃料在炸药爆炸驱动下形成燃料空气爆炸云团, 进而引燃爆炸, 对目标造成毁伤. 本文在前期提出的光滑离散颗粒流体动力学方法(SDPH)的基础上, 引入描述炸药由爆轰到膨胀整个过程的Jones-Wilkins-Lee状态方程及描述气体快速燃烧过程的EBU-Arrhenius燃烧模型, 建立了求解战斗部起爆、燃料抛撒和燃料二次引燃爆炸问题的新型SDPH方法. 设计了圆环形燃料颗粒在炸药爆炸驱动下运动抛撒的算例进行数值验证, 结果与理论相符; 对燃料空气炸药(FAE)云雾的形成和发展过程进行了数值模拟, 分析了云雾的形态, 并与实验结果进行对比, 符合较好, 同时分析了不同起爆方式对云雾团成型的影响; 最后, 在云雾团成型的基础上, 引入蒸发燃烧模型对FAE的燃烧爆炸过程进行了模拟研究. 结果表明, 本文建立的数学模型和计算方法可以较好的模拟燃料空气炸药抛撒成雾及云雾燃烧爆炸过程, 为该类武器装备的设计研究提供了较好的数值方法.     

Fast and slow modes of the propagation of the combustion front in heterogeneous systems

Experimental results are presented in favor of the existence of fast and slow modes of the propagation of the combustion front in diluted heterogeneous mixtures of reactive particles. A theoretical combustion model is proposed to explain the existence of these modes. The transition from the fast to the slow mode, which occurs in a narrow range of the degree of dilution of the mixture by inert powder, is associated with the break of a percolation cluster formed by reagent particles that are in direct contact with each other. After such a break of the cluster, the thermal energy of combusting particles is still insufficient to maintain the combustion wave. A sharp decrease in the front velocity in this case is associated with the necessity of heating inert regions inevitably appearing in its path.     

二维拉格朗日坐标系下气粒混合双向耦合对激波流场影响的计算

喷射颗粒与气体混合是内爆压缩领域的热点和难点. 针对喷射混合中的气粒双向耦合问题, 开展了理论建模、离散算法以及颗粒反馈对激波流场的影响研究. 建立了拉格朗日计算框架下的数学模型; 给出了耦合源项的离散算法; 开展了平面及汇聚构型条件下, 气粒双向耦合的数值模拟研究; 发现了颗粒反馈导致气体激波提速现象以及气区流场物理量分布形态的改变, 初步获得了量化分析结果. 本文建立的数学模型、计算方法和获得的新的物理认识, 为深入理解喷射混合现象、解决相关工程应用问题提供了重要理论支撑.     

Initiation of detonation by a high-voltage discharge in powdered explosives with nanosize inert admixtures

It is shown that admixtures of a copper nanopowder in a high-disperse low-sensitivity explosive of the FOX-7 type sharply increase the sensitivity of the mixture to the action of a high-voltage electric discharge and facilitate detonation. The percolation model of propagation of the electric breakdown over a powdered mixture with nanosize admixtures and the model of initiation of detonation by a high-voltage discharge in the mixture of a brisant explosive with an inert admixture are developed. These models are in qualitative and quantitative agreement with experimental data.     

Effects of Inert Particles on Liquid Phase Hydrogenation Over Nano-sized Catalysts

The effects of inert particles on the liquid hydrogenation over nano-sized Ni–B catalysts were investigated in a batch reactor. Nitrobenzene hydrogenation was used as a test reaction. The effects of stirring speed and the dispersant/catalysts ratio were investigated. Addition of inert particle in the reaction system of nano-catalysts could increase the reaction conversion significantly. The reaction conversion increased with increasing stirring speeding until 900-rpm, and then decreased. The addition of inert particle to the reaction system could prevent the agglomeration of nano-metals and disperse them over the entire reaction system. Nano-metals were physically attached on the external surface of the inert particles. In addition, the addition of inert particle may enhance the absorption rate of hydrogen in solvent, and resulting in the increase of reaction rate. Both are beneficial to the reaction conversion. The enhancement effect of Al₂O₃ is much greater than that of SiO₂.     

Effects of cosmic ray acceleration in relic grains of nanodiamonds in chondrites

A new mechanism of the formation of isotopic relations of anomalous Xe-HL component in nanodiamond grains of chondrites under conditions of the propagation of explosive shock waves from supernova outbursts is described, and the regularities of this mechanism are determined. Experimental evidence for the formation by supersonic turbulence of the power-law spectrum of particles with the index γ ∼ 1 in the carbondetonation supernova SnIa explosion is obtained, possibly opening up new prospects for investigating the processes of particle acceleration by shock waves.     

激光等离子体去除微纳颗粒的热力学研究

微杂质污染一直是影响精密器件制造质量和使用寿命的关键因素之一.对于微纳米杂质颗粒用传统的清洗方式(超声清洗等)难以去除,而激光等离子体冲击波具有高压特性,可以实现纳米量级杂质颗粒的去除,具有很大的应用潜力.本文主要研究了激光等离子体去除微纳米颗粒过程中的热力学效应:实验研究了激光等离子体在不同脉冲数下对Si基底上Al颗粒去除后的颗粒形貌变化,发现大颗粒会发生破碎而转变成小颗粒,一些颗粒达到熔点后发生相变形成光滑球体,这源于等离子体的热力学效应共同作用的结果.为了研究微粒物态转化过程,基于冲击波传播理论研究,得到冲击波压强与温度特性的演化规律;同时,利用有限元模拟方式研究激光等离子冲击波压强和温度对微粒作用规律,得到了颗粒内随时间变化的应力分布和温度分布,并在此基础上得到等离子体对颗粒的热力学作用机制.     

炸药爆炸作用下液体破碎后颗粒尺寸分布的研究

 对液体抛撒的液滴尺寸进行研究在军事和民用上是很重要的,国内刚开始使用激光散射仪开展此项研究工作。利用R. A. Dobbins等人的液体颗粒测量技术,研制了一套既简单又实用的测量液体抛撒过程中液滴尺寸的实验装置——激光散射仪。对于激光与液体微粒的相互作用,当微粒的反射与折射和吸收效应可被忽略时,可导出液体微粒对激光散射的光强公式。只要测量激光被微粒散射的光强,就可推算出微粒的Sauter平均直径。在使用激光散射仪测量液体抛撒液滴尺寸的实验中,用水代替爆炸抛撒液体,测量结果表明：液体抛撒二次破碎中,在固定位置测量到的云雾区液滴Sauter平均直径随测量时间的增加呈现出减小的趋势;而云雾区的宽度则随着与抛撒中心距离的增大而呈现出增加的趋势;云雾区前沿的液滴Sauter平均直径随着与抛撒中心距离的增加而呈现出先逐渐增大然后迅速减小的趋势。为便于比较,对燃料抛撒二次破碎进行了回收法测量和数值模拟计算,其测量与计算结果与用激光散射仪测量的结果有较好的一致性。     

Formation of double front detonations of a condensed-phase explosive with powdered aluminium

The performance characteristics of aluminised high explosive are considered by varying the aluminium (Al) mass fraction in a hybrid non-ideal detonation model. Since the time scales of the characteristic induction and combustion of high explosives and Al particles differ, the process of energy release behind the leading detonation wave front occurs over an extended period of time. Two cardinal observations are reported: a decrease in detonation velocity with an increase in Al mass fraction and a double front detonation (DFD) feature when anaerobic Al reaction occurs behind the front. In order to simulate the performance characteristics due to the varying Al mass fraction, the tetrahexamine tetranitramine (HMX) is considered as a base high explosive when formulating the multiphase conservation laws of mass, momentum, and energy exchanges between particles and HMX product gases. While experimental studies have been reported on the effect of Al mass fraction on both gas-phase and solid-phase detonations, the numerical investigations have been limited to only gas-phase detonation for the varying Al particles in the mixture. In the current study, a two-phase model is utilised for understanding the volumetric effects of Al mass fraction in condensed phase detonations. A series of unconfined and confined rate sticks are considered for characterising the performance of aluminised HMX with a maximum Al mass fraction of 50%. The simulated results are compared with the experimental data for 5–25% mass fractions, and the higher mass fraction behaviours are consistent with the experimental observations.     

Surface defects and their role in the shock sensitivity of cyclotrimethylene-trinitramine

The surface of cyclotrimethylene-trinitramine (RDX), a commonly used crystalline explosive was studied using atomic force microscopy (AFM). A diversity of surface defects was observed in different RDX particles as well as different parts of the same particle. Statistical analysis was undertaken to model the observed surface characteristics with the known shock sensitivities of the material. To quantify the surface defects observed on the crystalline surface of the RDX particles, surface roughness measurements were acquired. It was determined that there exists a statistically significant relationship between surface roughness characteristics and the shock sensitivity of the material.