Numerical Simulation of Explosive Dust Detonation with CE/SE Method

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.     

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.     

爆轰波在炸药-金属界面上的折射分析

针对爆轰波在炸药-金属界面上折射时由实验获得的金属折射冲击波压力与经典爆轰波极曲线理论预测的压力存在显著差异这一问题, 本文展开了进一步的理论和数值模拟分析研究. 首先通过分析指出经典爆轰波极曲线理论的缺陷, 并对爆轰波极曲线理论进行了改进, 改进爆轰波极曲线理论给出了炸药爆轰波折射类型以及折射冲击作用点处的压力值. 然后发展了一个基于次特征理论来数值求解爆轰反应流动控制方程的二阶中心型Lagrange方法, 并数值模拟了一个典型的炸药爆轰波折射实验. 改进爆轰波极曲线理论和数值模拟分析结果表明, 爆轰波折射类型有三种:反射冲击波的正规折射、带Mach反射的非正规折射、无反射波的正规折射, 并且金属折射冲击波压力值随入射角增大而单调减小.     

猛炸药RHT-901和钝感炸药IHE-2的爆轰波直角绕射

 采用高速转镜分幅相机和电探针技术研究了猛炸药RHT-901和钝感炸药IHE-2的爆轰波直角绕射图像和不同位置上的爆轰波传播时间。从研究得出，两种炸药都在拐角顶点附近绕射，爆轰波传播时间增长，爆速变小。但是两种炸药绕射爆轰波的状态不一样，钝感炸药IHE-2中爆轰波绕过直角时，在拐角顶点附近约10 mm范围内炸药未完全反应，猛炸药RHT-901中爆轰波绕过直角时未出现类似现象。两者相比，钝感炸药中绕射爆轰波速度变化大，波阵面曲率半径小，而猛炸药的绕射爆轰波速度变化小，波阵面曲率半径大。这说明炸药的爆轰波绕射与炸药的冲击感度、反应区宽度有关。     

化学反应和球面聚心爆轰波的相互作用

考察球面爆轰波聚心传播过程中,波阵面附近压力和温度不断升高引起化学反应进程的改变;对比氢氧可燃气体与氮气的数值模拟结果,分析化学反应对波面温度和压力的影响,从而考察Zeldovich理论预测聚心爆轰波后参数的精确性.数值结果表明,爆轰波聚心传播初期,放热的燃烧反应对波后热力学参数起主导作用;传播后期,波阵面趋近于对称中心时,吸热的气体解离反应变得非常活跃,解离反应对后期的汇聚压力影响不大,但会在很大程度上限制汇聚温度的升高.     

凝聚炸药爆轰波在高声速材料界面上的折射现象分析

凝聚炸药爆轰在边界高声速材料约束下传播时,爆轰波会在约束材料界面上产生复杂的折射现象.本文针对凝聚炸药爆轰波在高声速材料界面上的折射现象展开理论和数值模拟分析.首先通过建立在爆轰ZND模型上的改进爆轰波极曲线理论给出爆轰波折射类型,然后发展一种求解爆轰反应流动方程的基于特征理论的二阶单元中心型Lagrange计算方法来数值模拟典型的爆轰波折射过程.从改进爆轰波极曲线理论和二阶Lagrange方法数值模拟给出的结果看出,凝聚炸药爆轰波在高声速材料界面上的折射类型有四种:反射冲击波的正规折射、带束缚前驱波的非正规折射、带双Mach反射的非正规折射、带λ波结构的非正规折射.     

真实比热模型中铝粉尘两相爆轰波的数值研究

采用多流体模型对铝粉尘两相爆轰波进行数值模拟,研究颗粒能量计算方法对起爆和传播过程的影响.以前的固相颗粒能量的计算一般采用固定比热方法,本文采用随温度变化的真实比热.由于铝颗粒及其产物氧化铝的比热变化很大,模拟得到的爆轰波的速度、压力和波后参数变化和采用固定比热存在较大的差异.变比热计算得到的爆轰波压力、传播速度和实验结果更加接近,而固定比热的计算方法会对这些参数造成高估.对爆轰波的形成进行研究,发现起爆距离主要受起爆能量影响,但是相对于固定比热模型,采用变比热模型得到的起爆距离较短.     

拐角空间中悬浮铝粉尘爆轰后效的三维数值模拟

建立三维的铝粉-空气两相爆轰计算模型，采用时-空守恒元解元（CE/SE）方法求解，并开发了悬浮铝粉尘爆轰的三维数值模拟程序.基于消息传递接口（MPI）技术实现了程序的并行化设计.通过对激波管问题以及爆轰管中铝粉-空气两相爆轰实验的模拟验证程序的可靠性.对拐角空间中左侧浓度为368 g·m^-3的铝粉-空气混合物两相爆轰及其在拐角空间右侧和下方空气域内形成的冲击波和温压效应开展数值模拟，获得复杂空间内爆轰波或冲击波的传播、反射以及绕射过程.结果表明：两相爆轰在离铝粉尘区域2 m远的空气域内产生的后效冲击波能达到2.66 MPa的固壁反射压力，火球燃烧范围会超出初始铝粉尘区域约0.8 m，并且造成初始铝粉尘区域附近1.5 m范围内空气的温度高达1 600 K.模拟程序可用于铝粉尘爆轰的后效研究，对工业安全及其防护具有指导意义.     

激光作用铝靶爆轰波流场观测与理论分析

进行了强激光作用铝靶实验,采用纹影照相法,观察爆轰波流场演化过程,分析了爆轰波衰减规律。根据冲击波运动的自相似性,采用点爆炸模型描述了激光作用下爆轰波流场的演化,计算了波阵面速度、压力和温度。结果显示:爆轰波阵面沿迎着激光光源方向较快传播,波阵面形状由最初的半椭球形逐渐向半球形转变,在演化过程中扰动区结构复杂,存在多个密度间断层。在爆轰波开始传播阶段,波阵面的压力和温度较高但下降很快。     

炸药爆轰驱动超高速击波管的数值摸拟

 高能炸药（HE）柱壳沿轴向传播的稳定态爆轰，在置于炸药柱壳内部的泡沫塑料（工作流体）中产生很强的轴向击波，达到极高的压力和能量密度。适当设计，可使工作流体的流动接近一稳定态，与炸药爆轰以相同的相速度前进。击波阵面后的工作流体可用Nozzle流动方程很好地描述^[1]，Nozzle收缩段中的流动不受散开段流动的影响。利用这一性质，可以设计出达到极高压力和能量密度的超高速击波管，并且不受管壁物质强度的限制。数值模拟计算给出了上述稳定态物理图象，并显示出开始阶段轴向击波的形成过程及其后对稳定态的逼近，计算结果及物理图象与理论分析符合得很好。     

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.     

Blast waves in a cylindrical channel generated by the nonideal detonation of aluminum-Teflon-RDX high-density formulations

The pressure at the front and the pressure impulse of blast waves generated in a cylindrical tube by the expanding products of the nonideal detonation of low-porosity charges prepared by pressing of fine-grained powders of aluminum, Teflon, and RDX were measured. The measured parameters are compared to the same parameters of blast waves produced by the detonation of TNT charges of identical mass. The relative quantities were used to evaluate the effectiveness of blast waves with respect to those generated by TNT. Mixed compositions differing in the shape (brand) of the aluminum powder particles and the ratio between the components at 30% RDX are studied. It is shown that, for the investigated compositions, the pressure at the leading front of the wave exceeds the pressure achieved during TNT explosion on average by 10–30%, almost independently of the distance traveled along the tube in the range from 0.8 to 3.8 m. The dependence of the wave amplitude on the particle shape and aluminum content was weak. In the same range of distances, the relative pulse pressure increases strongly, from 0.5 to 2.1 and higher, mainly due to an increase in the width of the wave. This result is of interest from the point of view of achieving a high pressure impulse of the blast wave in an area remote from the charge. The obtained data suggest that RDX mainly reacts in the detonation wave, with the chemical transformation of Teflon and aluminum in the detonation wave and near-to-charge zone occurring, if at all, to a small extent. On the contrary, as the blast wave front moves through the channel, the burning of aluminum in the fluoride formed during the decomposition of Teflon provides an appreciable support to the blast wave, causing a significant increase in the pressure impulse.     

空气中激光支持爆轰波实验及理论分析

为了研究激光击穿空气产生的等离子体爆轰波形成机制和传播规律,利用高能量CO2激光器产生强激光,进行了空气中产生激光支持等离子体爆轰波实验。实验中:设置了诱导靶板,用于诱发和定位空气中的激光支持爆轰波;以激光器升压过程球隙放电产生的光信号作为触发源,触发高时间分辨率(纳秒级)的高速相机,记录了激光支持爆轰波的成长和传播全过程。分析了激光支持爆轰波的形成机理和传播规律。采用C-J爆轰理论,计算了激光支持爆轰波的压力和温度。研究结果表明:激光支持等离子体爆轰波形成初期,等离子体爆轰波发光体为球形;随着时间增加,等离子体爆轰波发光体的形状类似流星,且头部为等离子体前沿吸收层,亮度较高,而尾部等离子体温度较低,亮度较弱。等离子体爆轰波高速向激光源的方向移动,爆轰波速度高达18 km/s,温度约为107K。随着激光强度的减弱,爆轰波速度迅速按指数规律衰减,当爆轰波吸收的激光能量不能有效支持爆轰波传播时,爆轰波转变为冲击波。     

Calculation of shock wave propagation in water containing reactive gas bubbles

The entry of a shock wave from air into water containing reactive gas (stoichiometric acetylene–oxygen mixture) bubbles uniformly distributed over the volume of the liquid has been numerically investigated using equations describing two-phase compressible viscous reactive flow. It has been demonstrated that a steady-state supersonic self-sustaining reaction front with rapid and complete fuel burnout in the leading shock wave can propagate in this bubbly medium. This reaction front can be treated as a detonation-like front or “bubble detonation.” The calculated and measured velocities of the bubble detonation wave have been compared at initial gas volume fraction of 2 to 6%. The observed and calculated data are in satisfactory qualitative and quantitative agreement. The structure of the bubble detonation wave has been numerically studied. In this wave, the gas volume fraction behind the leading front is approximately 3–4 times higher than in the pressure wave that propagates in water with air bubbles when the other initial conditions are the same. The bubble detonation wave can form after the penetration of the shock wave to a small depth (~300 mm) into the column of the bubbly medium. The model suggested here can be used to find optimum conditions for maximizing the efficiency of momentum transfer from the pressure wave to the bubbly medium in promising hydrojet pulse detonation engines.     

Embedded particle size distribution and its effect on detonation in composite explosives

This paper discusses the effects of stochastically varying inert particle parameters on the long-term behaviour of detonation front propagation. The simulation model involves a series of cylindrical high explosive unit cells, each embedded with an inert spherical particle. Detonation shock dynamics theory postulates that the velocity of the shock front in the explosive fluid is related to its curvature. In our previous work, we derived a series of partial differential equations that govern the propagation of the shock front passing over the inert particles and developed a computationally efficient simulation environment to study the model over extremely long timescales. We expand upon that project by randomising several properties of the inert particles to represent experimental designs better. First, we randomise the particle diameters according to the Weibull distribution. Then we discuss stochastic particle spacing methods and their effects on the predictability of the shock wave speed. Finally, we discuss mixtures of plastic and metal particles and material inconsistency among the particles.     

凝聚炸药中超压爆轰的实验研究

 采用飞片碰撞技术，在TNT/RDX（40/60）炸药中获得了2.5倍于正常爆轰的最大超压值，得到了超压爆轰下爆轰产物物态方程p=Aρ^{k+A₁(p-p_J)}（p－爆压，单位GPa，ρ－密度，单位kg/m³，A=ρ_J/ρ^k_J，p_J=27.06 GPa，ρ_J=2.3×10³ kg/m³，k=2.77，A₁=2.7×10^-3 GPa^-1，下表J代表正常爆轰状态）。该方程还可以较好地描述超压爆轰产物的二次冲击状态。     

Weak detonation in mixtures of phlegmatized RDX with aluminum

The Zel’dovich theory predicts the possibility of realization of self-sustained weak detonation in systems with nonmonotonic energy release. The present paper describes experiments aimed at detecting such a regime of detonation in mixtures of phlegmatized RDX with PP-1 and PAP-2 aluminum powders. The mass fraction of aluminum was 20%. To examine the detonation regimes, 70-mm-in-diameter charges of these mixtures were initiated with powerful triangular pressure pulses, which gave rise to attenuating overdriven detonation waves. The pressure profiles were recorded at various distances from the initiation plane (from 10 to 80 mm). Specific features of the time evolution of the detonation wave profile indicative of the existence of a supersonic flow region arising not later than 0.15 μs behind the shock front were revealed. The supersonic character of the flow behind an intermediate C-J plane is an inherent characteristic of self-sustained weak detonation; i.e., direct experimental evidence for the existence of weak detonation in RDX-aluminum mixtures was obtained.     

Detonation simulations in supersonic flow under circumstances of injection and mixing

The unsteady, reactive Navier-Stokes equations with a detailed chemical mechanism of 11 species and 27 steps were employed to simulate the mixing, flame acceleration and deflagration-to-detonation transition (DDT) triggered by transverse jet obstacles. Results show that multiple transverse jet obstacles ejecting into the chamber can be used to activate DDT. But the occurrence of DDT is tremendously difficult in a non-uniform supersonic mixture so that it required several groups of transverse jets with increasing stagnation pressure. The jets introduce flow turbulence and produce oblique and bow shock waves even in an inhomogeneous supersonic mixture. The DDT is enhanced by multiple explosion points that are generated by the intense shock wave focusing of the leading flame front. It is found that the partial detonation front decouples into shock and flame, which is mainly caused by the fuel deficiency, nevertheless the decoupled shock wave is strong enough to reignite the mixture to detonation conditions. The resulting transverse wave leads to further mixing and burning of the downstream non-equilibrium chemical reaction, resulting in a high combustion temperature and intense flow instabilities. Additionally, the longitudinal and transverse gradients of the non-uniform supersonic mixture induce highly dynamic behaviors with sudden propagation speed increase and detonation front instabilities.