用环形激波聚焦实现爆轰波直接起爆的数值模拟

利用基元反应模型和有限体积法对环形激波在可燃气体中聚焦实现爆轰波直接起爆进行了数值模拟。研究结果表明,标准状态下的氢气-空气混合气体在马赫数为3.1以上的环形激波聚焦产生的高温高压区作用下会诱发可燃气体的直接起爆形成爆轰波,爆轰波与激波和接触间断相互作用产生了复杂的波系结构;爆轰波爆点位置在对称轴上并不是固定的点,而是随着初始激波马赫数的变化而发生移动;可燃气体初始温度和压力对起爆临界马赫数都有影响,但是初始温度的影响大得多。     

激波聚焦诱导点火和爆轰的数值研究

以二维轴对称多组分Euler方程为基础,采用非正交结构化网格和改进的波传播算法,模拟了激波在抛物形反射壁面聚焦反射诱导点火和爆轰的过程,描述了其流场形态。讨论了预混气组成、入射激波强度及反射壁面形状对点火和爆轰的影响。结果表明,激波在抛物形反射壁面顶点处聚焦反射可形成局部高温高压区域,该区域在一定条件下可点燃预混气甚至形成爆轰,其中低稀释剂浓度的预混气、较大的入射激波Mach数和较深的反射壁面有利于可燃预混气形成爆轰。     

Numerical investigation of axisymmetric shock wave focusing over paraboloidal reflectors

The problem of a plane shock wave incident to a paraboloidal reflector is numerically investigated. The numerical solver used is developed by an improved, implicit, upwind total variation diminishing scheme in a finite-volume approach. The real-gas effect is taken into account if high temperature occurs. The solver is validated on four test problems. The complicated flow fields of axisymmetric shock wave focusing for different-depth reflectors at various incident shock Mach numbers are studied. An interesting result of a maximum pressure happening at the reflector center is found. This is due to the occurrence of an implosion phenomenon. A maximum temperature might occur at the reflector center or at other locations, depending on the incident shock Mach number and the reflector depth. Moreover, vortical flows induced by shock wave focusing and their formation mechanism are explored. It was found that the vortices near the reflector are caused by a ring-shaped shock/slipline interaction. Owing to the slipline on the symmetry axis, a jet flow is induced, resulting in the formation of vortices near the symmetry axis. Received 13 January 1998 / Accepted 10 November 1998     

Numerical investigation of toroidal shock wave focusing in a cylindrical chamber

In this paper, focusing of a toroidal shock wave propagating from an annular shock tube into a cylindrical chamber was investigated numerically with the dispersion controlled dissipation (DCD) scheme. The first case for an incident Mach number of 1.5 was conducted and compared with experiments for validation. Then, several cases were calculated for higher incident Mach numbers varying from 2.0 to 5.0, and complicated flow structures were observed. The numerical study was mainly focused on two aspects: focusing process and flow structures. The process, including diffraction, focusing, and reflection, is displayed to reveal the focusing mechanism, and the flow structures at different incident. Mach numbers are used to demonstrate shock reflection styles and focusing characteristics. PACS 47.40.Ki; 47.40.Nm; 52.35.Tc     

Numerical investigation of inviscid shock wave dynamics in an expansion tube

Highly complicated shock wave dynamics has been numerically calculated by solving the Euler equations for a circular shock tube suddenly expanded three times of the original tube diameter atx=0. Shock waves of different shock Mach number,M _s =1.5 and 2.0, have produced remarkably distinct blast jet structures. A planar shock wave took its final form after the blast by repeated Mach reflections of the blast wave: the first one at the wall and the second one at the central axis. The central Mach disc overtook and merged with the annular Mach stem before the planar shock wave was formed. In contrast to the blast wave which would propagate spherically in an open space, the present blast wave undergoes complex morphological transformation in the restricted flow passage, resulting in an unstable and oscillatory blast jet structure of highly rotational nature. The slipstream tube emanating from the shock tube exit corner decomposed into a chain of small vortex rings that interacted with the barrel shock of the jet, which caused periodic collapse of the jet structure. The finite volume-FCT formulation equipped with the time-dependenth-refinement adaptive unstructured triangular mesh technique in the present paper has contributed to resolution of the intricate physical discontinuities developing in the blast flow fields.     

多循环脉冲爆震发动机流场数值研究

针对二维带有收敛扩张喷管的脉冲爆震发动机模型，采用带基元化学反应的Euler方程组和H2、空气的9组分20基元反应，对发动机在前六个工作循环的流场进行了数值模拟。通过对前几个循环流场进行比较，发现脉冲爆震发动机在第五个循环后流场就基本稳定，单循环得到的流场和多循环稳定后的流场有很大的差别，同时喷管对发动机内流场影响特别大。     

爆炸冲击合成纳米碳化钛的研究

本文利用奥克托今炸药（HMX）作为高温、高压源,二氧化钛（TiO₂）和活性炭（C）作为前驱体,采用爆炸冲击合成的方法制备纳米碳化钛（TiC）粉末。运用X射线衍射分析仪(XRD)、X射线能谱分析仪(EDS) 及扫描电子显微镜(SEM) 对样品进行了分析与表征。探讨了爆炸冲击波作用下TiC的合成机理。结果表明:XRD和EDS测试值与理论值相符性很好,样品中同时含有TiC和TiC_x（x＜1）;SEM照片显示TiC和TiC_x（x＜1）的粒径均小于50 nm,样品中存在微米级的球形团聚体;爆炸冲击合成TiC属于特殊的固相反应,其物质扩散速度和反应速度大大提高。     

Numerical investigation of two-phase rotating flow

Finite difference solutions of the two-fluid equations of motion for a particle (droplet)-fluid mixture in a rotating finite axisymmetric cylinder are presented. The numerical method, which can be regarded as an extension of the Harlow & Amsden approach, employs forward time and centred space discretization and treats implicitly the pressure, Coriolis and volume flux terms. The computed flow fields are examined via a detailed comparison to previous analytic approximations, which illuminates both the physical and numerical aspects and the validity of these approximations.     

Steady shock wave reflections in thermochemical nonequilibrium flows

The shock wave reflection phenomena in hypersonic steady air flows, including thermochemical nonequilibrium effects, are investigated. The main objectives are to study the influence of these effects on the two shock wave reflections (regular and Mach reflections), on the Mach stem height and on the hysteresis behavior. The air computations are performed using a multi-block MUSCL-TVD finite-volume scheme. The computational results with and without thermochemical effects in the air mixture flow at an upstream Mach number equal to 7 are compared. The comparison reveals a strong dependence of the transition angles, of the height and location of the Mach stem on the physical modeling of the gas flow. Received 17 February 2000 / Accepted 30 August 2000     

Pseudo-steady oblique shock wave reflections over water wedges

A preliminary experimental investigation of the reflection phenomenon of a planar shock wave over a water wedge is reported. The experimental investigation was conducted using a specially designed shock tube which was capable of being tilted from a horizontal situation to a vertical one in an accuracy of 0.1°. The four well-known types of pseudo-steady oblique shock wave reflections were observed. In addition, it has been found that the actual wedge angles at which the regular reflection transitions to a Mach reflection differ from those measured over a solid wedge.     

激波诱导火焰失稳与爆轰的条件研究

采用九阶WENO和十阶中心差分格式数值求解激波与火焰作用过程,考察了激波强度、火焰尺寸对激波与球形火焰作用过程的影响。结果表明,增大激波强度或火焰尺寸均可在流场中引发爆轰,但激波强度的影响更大,并且其引发的爆轰可使火焰迅速膨胀,放热率提高,从而影响燃烧特性;此外,爆轰波传播过程中会迅速消耗可燃预混气,合并原有的反射激波,并在流场中形成局部高压区,极大地改变流场结构。     

Numerical investigation on evolution of cylindrical cellular detonation

Cylindrical cellular detonation is numerically investigated by solving two- dimensional reactive Euler equations with a finite volume method on a two-dimensional self-adaptive unstructured mesh. The one-step reversible chemical reaction model is applied to simplify the control parameters of chemical reaction. Numerical results demonstrate the evolution of cellular cell splitting of cylindrical cellular detonation explored in experimentas. Split of cellular structures shows different features in the near-field and far-field from the initiation zone. Variation of the local curvature is a key factor in the behavior of cell split of cylindrical cellular detonation in propagation. Numerical results show that split of cellular structures comes from the self-organization of transverse waves corresponding to the development of small disturbances along the detonation front related to detonation instability.     

Numerical investigation on three-dimensional shock wave reflection over two perpendicularly intersecting wedges

The three-dimensional (3D) shock wave reflections over two perpendicularly intersecting wedges are numerically studied in this paper, using the finite volume method which is based on the MUSCL-Hancock interpolation technique and self-adaptive unstructured mesh. Two kinds of 3D Mach stem structures are demonstrated by the numerical simulations for different shock Mach numbers and wedge angles. A four-shock or three-shock wave configuration appears in the vicinity of the corner of the wedges.     

Numerical investigation of the effect of rotational relaxation rate on the nitrogen shock wave structure

The nitrogen rotational relaxation process is numerically investigated on the basis of the Monte-Carlo method and the calculation of the classic three-dimensional equations of motion of rigid-rotator molecules. The dependence of the relaxation parameterZ _R on the initial values of the translational and rotational temperaturesT _t andT _R and the asymmetry parameter in the molecular interaction potential is obtained. The problem of the shock wave structure is solved using the Pullin phenomenological model whose parameters are determined on the basis of the solution of the relaxation problem with exact calculation of the molecular interaction. The dependence of the flow fields and the relative thickness of the density profile on the quantityZ _R is obtained and the calculated data are compared with the results of experiments. It is shown that the data are in better agreement for larger values of the asymmetry parameter.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 4, pp. 159–167, July–August, 1995.     

Super-equilibrium increase of chemical reaction rate in the detonation front and other effects in the detonation wave initiated by a shock wave

In the present work the problem of detonation wave formation in a shock tube was considered in one-dimensional formulation. The Monte Carlo non-stationary method of statistical simulation (MCNMSS), also known as DSMC, was used for simulation. The method automatically takes into account all details of mass and heat transfer. At an initial moment, the low-pressure channel (LPC) of the shock tube was filled with gas A while the high-pressure chamber (HPC) was filled with gas C. The cross-sections of the HPC and LPC, as well as the temperatures of gases A and C were equal to each other. At the beginning of the simulation the ratio of pressures in the HPC and LPC was equal to 100. It was assumed that chemical reactions $\mathrm{{A}}+\mathrm{{M}} \rightarrow \mathrm{{B}}+\mathrm{{M}}$ ( $\mathrm{{M}}=\mathrm{{A}},\, \mathrm{{B}}$ and $\mathrm{{C}}$ ) took place. The ratio of molecular masses of gases $\mathrm{{A}},\, \mathrm{{B}}$ and $\mathrm{{C}}$ was taken as 20:20:1. Different reaction thresholds were considered. For the case of a low reaction threshold, the velocity of the resulting detonation wave was found to be higher than the Chapman–Jouguet velocity. A region with constant values of flow parameters inside product was observed. An increase of the reaction threshold led to disappearance of this region and gave rise to something similar to an expansion wave, with peaks of flow parameters at the leading part of the detonation wave. The values of these peaks were found to be constant in time. The velocity of the detonation wave became appreciably lower than the Chapman–Jouguet velocity. Further increase of the reaction threshold led to disappearance of detonation. The reactions $\mathrm{{A}}+\mathrm{{B}} \rightarrow \mathrm{{B}}+\mathrm{{B}}$ and $\mathrm{{A}}+\mathrm{{C}}\rightarrow \mathrm{{B}}+\mathrm{{C}}$ turned out to be very important for initiation of detonation.     

高速转动圆盘流动数值模拟研究

重点研究高速离心压气机叶轮与机匣间的间隙流动及其温度分布。研究将离心压气机简化为高速转动圆盘,搭建了相关实验平台,并开展了相应的数值模拟研究。通过改变转动圆盘的转速和轴向进入的冷却流的流量,研究了转速和流量对于间隙内温度和速度分布的影响。结果显示,转速是影响温度变化的最主要因素,转速越大,温度越高;同等幅度的流量变化对温度的影响则较小。研究发现,在实验和模拟对应的大雷诺数条件下,无量纲的速度分布基本不受到圆盘转速、冷却流量和温度场的影响。     

Numerical simulation of shock wave intersections

A large number of papers, generalized and classified in [1, 2], have been devoted to unsteady gas flows arising in shock wave interaction. Experimental results [3–5] and theoretical analysis [6–9] indicate that the most interesting and least studied types of interaction arise in cases when there are several shock waves. At the same time, nonlinear effects, which depend largely on the nature of the shock wave intersections, become appreciable. Regions of existence of different types, of plane shock wave intersections have been analyzed in [10–13]. It has been shown that in a number of cases the simultaneous existence of different types of intersections is possible. The aim of the present paper is to study unsteady shock wave intersections in the framework of a numerical solution of the axisymmetric boundary-value problem that arises in the diffraction of a plane shock wave on a cone in a supersonic gas flow. Flow regimes that augment the experimental data of [3–5] and the theoretical analysis of [9] are considered.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 134–140, September–October, 1986.     

用于冲击波和爆轰物理实验中的声光开关

针对冲击波和爆轰物理实验中对光开关的使用要求,提出了一种基于布拉格衍射效应的行波式声光开关,得到了声光开关的开关波形、消光比、抗激光损伤特性及能量利用率等。结果表明,与传统的普克尔电光开关相比,声光开关有效地消除了开关光信号顶部的振铃现象,消光比达到5000∶1,同时减小了开关体积、提高了开关工作稳定性。声光晶体抗激光损伤阈值大于2.26 kW/cm2,开关能量利用率达70％。开关触发固有延迟和上升沿时间分别为900和440 ns,满足测试系统对开关同步性的要求。另外开关光信号宽度可由触发信号任意调节,能满足不同测试情况的需要。     

正向爆轰驱动高焓激波风洞的数值模拟

对充满氢氧可燃气体、带扩容腔的正向爆轰驱动的激波风洞进行了数值模拟。计算采用了欧拉方程,频散可控耗散差分格式（DCD）和改进的二阶段化学反应模型。在扩容腔附近采用二维轴对称计算模型,而在驱动段和被驱动段的直管道部分则采用一维计算模型。本文分析了爆轰波在管道中的传播、反射和绕射过程。计算结果表明扩容腔的尺寸对爆轰波的传播、反射、汇聚等起着决定性的作用;带扩容腔的正向爆轰驱动的激波风洞能够得到平稳的持续时间较长的气流,提高了实验的精确度和可重复性。