周期性非均匀介质中气相爆轰波演变模式研究

气相爆轰波在周期性非均匀介质中的起爆, 稳态传播和失效机制都极为复杂, 很多物理机制尚不明确, 是当前爆轰物理领域研究的热点和难点. 本文使用反应欧拉方程和两步化学反应模型对爆轰波在非均匀介质中的传播机理进行了数值模拟研究, 非均匀性由横向周期性分布的温度扰动体现, 重点分析不同波长、不同幅度的温度扰动对波阵面波系结构的影响. 计算结果表明, ZND爆轰波在温度扰动下向胞格爆轰波的转变主要受制于两种竞争性因素: 一是爆轰波内在的不稳定性; 二是温度扰动的波长和幅度, 前者是内因, 后者是外因. 温度扰动的存在抑制横波的发展, 延迟了ZND爆轰波向胞格爆轰波的演化, 并且内在不稳定性的增加可以减慢这种延迟现象. 这说明, 温度扰动可以在一定的范围内抑制胞格不稳定性的发展, 但是不能够终止这一过程. 温度的不连续性使得爆轰波阵面更为扭曲, 并在横波附近存在较弱的三波点结构, 即温度扰动可增加爆轰波固有的不稳定性, 改变爆轰波阵面的传播机理. 幅值较大的人工温度扰动可抑制爆轰波的传播和爆轰波自身的不稳定性. 爆轰波阵面胞格结构的形成取决于温度扰动与其自身的不稳定性.      

斜爆轰波面上复杂结构的数值研究

利用欧拉方程和单步化学反应模型, 对斜爆轰波进行了数值模拟, 重点研究了斜爆轰波面上多维复杂结构的形成机理. 数值结果显示在斜爆轰波面上, 存在两种小尺度的激波和火焰耦合结构: 第1种结构由一道横波和三角形火焰组成, 是斜爆轰波中特有的结构; 第2种结构由两道横波和凸起的火焰面组成, 类似于正爆轰波面上的胞格结构. 数值结果表明这两种结构具有相同的形成机理, 而且能够相互转化, 它们的形成和发展过程受到来流马赫数和化学反应放热速度等参数的影响.      

爆轰波平掠惰性气体界面及其解耦现象的数值研究

采用基元化学反应模型和迎风TVD格式,数值研究了爆轰波平掠惰性气体界面时的物理现象及其作用机制,并用点隐方法克服化学反应源项引起的计算刚性。数值结果显示,当爆轰波平掠过惰性气体界面时,形成了爆轰波、界面、透射激波以及稀疏波相互作用的现象。在高N2比例稀释的可燃混合气体情况下,当爆轰波平掠过特定惰性气体界面时,它与惰性气体界面相互作用产生的稀疏波可以导致爆轰波的解耦。     

Simulation numérique des détonations à double structure cellulaireNumerical simulation of detonations with double cellular structure

We present the results of numerical two-dimensional simulations of detonation cellular structures under non-monotonous heat release provided by a chemical reaction comprising two successive exothermic steps. The influence of the rate of the second step of chemical reaction on the detonation cellular structure has been investigated. Our simulations are the first that reproduce a cellular structure composed of two clearly distinct sets of cells with different characteristic sizes where fine cells completely fill up larger ones, as has been observed experimentally. To cite this article: V. Guilly et al., C. R. Mecanique 334 (2006).     

Two-cell detonation: losses effects on cellular structure and propagation in rich H2–NO2/N2O4–Ar mixtures

Detonation experiments in H₂–NO₂/N₂O₄–Ar mixtures (Equivalence ratio 1.2 and initial pressure lower than 0.1 MPa) confined in a tube of internal diameter 52 mm reveal two propagation regimes depending on initial pressure: (1) a quasi-CJ regime is observed along with a double cellular structure at high pressures; (2) at lower pressures, a low velocity detonation regime is observed with a single structure. Transition between this two regimes happens when the spinning detonation of the larger cell vanishes. Each detonation regime is characterized by velocity and pressure measurements and cellular structure records. Coherence between all experimental data for each experiment leads in assumption that losses are responsible for the transition between one regime to another. In a second part, we study such behaviour for a two-step mixture through numerical simulations using a global two-step chemical kinetics and a simple losses model. Numerical simulations qualitatively agree with experiments. Both detonation regimes with their own cellular structures are reproduced.     

直管内胞格爆轰的基元反应数值研究

基于基元反应和二维欧拉方程，对直管内胞格爆轰进行了数值模拟。采用5阶WENO(weighted essentially nonoscillatory scheme)求解对流项，采用2阶附加半隐的龙格-库塔法处理化学反应源相引起的刚性。获得了密度、压力、温度和典型组元质量分数流场及数值胞格结构等。结果表明:网格精度的差异明显影响胞格的规则性和爆轰的平衡模数，随着网格尺度的减小，胞格由不规则变为规则。预混气组成、初压、初温及管道宽度给定，三波点数收敛为确定值。足够强度的初始扰动可再现胞格爆轰，最终形成的自持胞格爆轰模数与初始扰动的形状、大小、位置均无关。沿胞格中心线，爆轰波速度变化范围为0.88DCJ~1.5DCJ，爆轰波平均速度与CJ爆轰速度仅偏差0.88％。峰值压力与初压之比为14~50。计算爆轰波平均速度、胞格宽长比与实验值基本一致，但计算胞格宽度比实验值略小。数值模拟加深了对横波的产生和发展、未反应气囊、爆轰胞格的二次起爆等胞格爆轰特性的认识。     

气相爆轰在T形管中传播新现象的实验研究

对2H2/O2/Ar系统爆轰波在T形管(截面为40mm×40mm)中传播现象进行了实验研究.用烟迹片记录了T形管中爆轰波的胞格结构,用压电传感器记录了分叉口附近指定点压力时间曲线,得到了爆轰波在分叉口附近的平均速度和胞格图案演变.结果表明:初压P0≥2.67kPa,在水平和垂直支管下游区域(距离分叉口约3.5—6倍方管截面边长),分叉口影响消失,爆轰波恢复稳定,且强度基本保持不变.在分叉口绕射过程中,爆轰波在膨胀区中衰减,诱导激波阵面弯曲.两个支管中发生马赫反射,三波点迹线清晰可见.该传播特性是爆轰波的诱导激波和横波共同作用的结果.分叉口附近的胞格结构先消失再恢复,在无胞格和平衡胞格之间的区域存在细密胞格的过渡区,表征了在诱导激波与化学反应阵面分离后的区域中出现二次点火.P0=2.00kPa,水平支管中稳定自持爆轰能重建,垂直支管中爆轰熄灭.P0<2.00kPa,分叉口上游已不能形成稳定爆轰.还对胞格结构中的几个特征参数进行了测量,并初步分析了P0对这些参数的影响.     

多障碍物通道中激波诱导气相爆轰的数值研究

应用数值模拟方法,研究了直通道中激波经过多块矩形障碍物时诱导 H2/O2混合气体起爆的物理机制. 研究表明：在前导激波强度不足以诱导波后气 体直接起爆的条件下,经过激波压缩的可燃气体也可能在远离激波的障碍物之间的凹槽部位 起爆;障碍物表面产生的压缩波、膨胀波和气流滑移面对可燃气体的起爆、爆轰波的形成和 传播过程有重要的影响;添加不同稀释比的氮气可以影响爆轰波后流场的温度分布;增加障 碍物的间距可以改变可燃气起爆位置.     

旋转爆轰胞格结构的实验和数值研究

对爆轰波在环形圆管(预混气体为2H2/O2/Ar)内的传播分别进行了实验和数值研究。实验研究 采用烟迹板记录了环形圆管内爆轰波的胞格结构。数值计算利用二阶附加半隐的Runge-Kutta法和五阶 WENO格式分别离散欧拉方程的时间和空间导数项,采用基元反应简化模型描述化学反应过程,得到了旋转 爆轰的流场及数值胞格结构。实验和数值模拟结果表明:爆轰波在圆环管中传播时,由于圆环的内壁发散、外 壁收敛,圆环内侧爆轰强度小于外侧,胞格尺寸较大;内侧OH 的分布区域大于外侧,浓度较低。旋转爆轰的 这种性质,使爆轰波能以稳定的角速度绕轴旋转。     

Interprétation de la double structure observée dans l'onde de détonation du nitrométhane gazeux

Calculations of the reaction zone of the detonation of gaseous nitromethane, either pure or diluted with oxygen, in the range of equivalence ratio Φ between 0.1 and 1.75, show that for 1.75⩾Φ⩾1.3 the chemical energy is released in two main successive reaction steps characterized by very different induction times. These results corroborate the experimental observations of two levels of cellular structures in the same range of equivalence ratios. To our knowledge this work is the first which deals with the problem of nonmonotonous chemical energy release behind the leading shock of a detonation wave.     

弯管内爆轰波传播的流场显示和数值模拟

采用激光纹影系统拍摄了爆轰波在不同位置的流场照片. 用二阶附加半隐的龙格- 库塔法和五阶WENO格式 分别离散欧拉方程时间和空间导数项,用基元反应来描述爆轰化学反应过程,获得了压力、 温度、典型组元质量分数分布及数值胞格结构和爆轰波平均速度. 结果表明：受壁面稀疏波 和压缩波影响,爆轰波阵面发生畸变. 但由于弯管曲率半径较大,未出现爆轰波熄灭. 靠近 凹壁面的激波强度大于凸壁面侧,且凹壁面侧的反应区宽度较凸壁面侧要窄. 弯管出口处的 三波点数目较入口处减少,爆轰波衰减. 在出口直段,受扰动的爆轰波可恢复为自持爆轰波. 爆轰波流场、胞格结构、平均爆轰波速度的计算和实验结果定性一致.     

Three-dimensional parallel simulation of cornstarch-oxygen two-phase detonation

Numerical simulations were performed with a parallel computer to solve for the behavior of a three-dimensional gas-solid two-phase detonation. The numerical method is a second-order modified Harten-Yee TVD upwind scheme and time integration uses a first order Euler integration. A two-step chemical reaction model represents the reaction of cornstarch-particles and oxygen. The numerical results show that a periodic two-headed detonation appears with a three-dimensional propagation mechanism before and after a triple point collisions. A comparison between the numerical and experimental results reveals that the detonation velocity of numerical results agrees well with that of experimental results. Received 8 September 1999 / Accepted 7 May 2000     

Structure cellulaire de la détonation des mélanges H2–NO2/N2O4Cellular structure of the detonation of gaseous mixtures H2–NO2/N2O4

Calculations of the detonation reaction zone of gaseous reactive mixtures of NO₂/N₂O₄ as oxidizer and H₂, CH₄ or C₂H₆ as fuel, in the range of equivalence ratio Φ between 0.5 and 2, show that, for Φ?1, the chemical energy is released in two distinct and successive exothermic steps with different chemical induction times. The first exothermic stage is mainly due to the reaction NO₂+H→NO+OH, NO being the main oxidizer of the second one.The experimental study conducted on the same range of equivalence ratio (0.5?Φ?2) shows that, for Φ?1, the detonation wave of these mixtures contains a double set of cellular structures. A similar result had already been obtained with the detonation of gaseous Nitromethane, the NO₂ group being here included in the molecule. Consequently, the oxidizer NO₂ being either initially separated from the fuel or included inside the molecule of a monopropellant (Nitromethane) is responsible, because of its specific chemical kinetics, of a chemical energy release in two main steps and of the existence of a double cellular structure in the detonation wave for the same range of equivalence ratio. These results reinforce the assumption that the cellular structure of the detonation finds its origin in the strong rates of chemical energy release inside the reaction zone. To cite this article: F. Joubert et al., C. R. Mecanique 331 (2003).     

氢氧爆轰波在变截面扩张管道中传播的数值模拟

采用二阶精度频散控制耗散格式(DCD)和8组分20个方程的基元反应模型,对轴对称变截面管道中氢氧爆轰波传播进行数值模拟。结果表明,爆轰波传播至突变截面扩张管道时,由于稀疏波的作用可能会使爆轰波局部熄爆甚至完全熄爆,对于某些敏感度高的反应气体爆轰波可以二次起爆。而在渐变截面扩张管道爆轰波相对不易熄爆。     

不稳定性对爆轰波楔面马赫反射的影响规律研究

采用一种两步化学反应模型对胞格爆轰波的楔面马赫反射过程进行了数值研究,从而澄清和解释胞格不稳定性对马赫反射发展模式和自相似性的影响。考虑到反应欧拉方程源项的刚性问题,本文采用附加RungeKutta方法耦合非刚性对流项和刚性反应源项,对流项的离散采用五阶精度的WENO格式。计算结果表明,对于稳定胞格爆轰波而言,其马赫反射过程本质上与ZND爆轰波的马赫反射是一致的,整体上不存在自相似性,胞格不稳定性只是造成了三波点轨迹线局部小振幅的波动。在楔面顶点附近,由于马赫杆是强过驱的,爆轰波的马赫反射过程是自相似的。在远场,爆轰波马赫反射的三波点轨迹线渐近的趋向于一条直线,说明重新获得了自相似性。对于不稳定的爆轰波,由于自身的不稳定性可以与马赫反射的强度相匹配,定义其三波点的轨迹是困难的,进行自相似性分析没有意义。     

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.      

Numerical study of three-dimensional detonation structure transformations in a narrow square tube: from rectangular and diagonal modes into spinning modes

Three-dimensional (3-D) detonation structure transformations from rectangular and diagonal modes into spinning modes in a narrow square tube are investigated by high-resolution simulation. Numerical simulations are performed with a Riemann solver of the HLLC-type, new cell-based structured adaptive mesh refinement data structure, high-order, parallel adaptive mesh refinement reactive flow code. A simplified one-step kinetic reaction model is used to reveal the 3-D detonation structure. The four different types of initial disturbances applied in the ZND profiles lead to the structures of rectangular in phase, rectangular out of phase, rectangular partial out of phase and diagonal, respectively, during the initial stages of detonation propagation. Eventually, all these detonation structures evolve into the self-sustained spinning detonations. The asymmetric disturbance leads to a stable spinning detonation much faster than the rest. The important features in the formation of spinning detonation are revealed using a 3-D visualization, and a remarkable qualitative agreement with experimental and numerical results is obtained with respect to the transverse wave dynamics and detonation front structures. The transverse wave collisions produce the unburnt gas pockets and the energy to sustain the detonation front propagation and distortion. The periodic pressure oscillation of front plays a complex role as it shifts the reaction zone structure with an accompanying change in the driving energy of transition and the detonation parameters which result in the more distorted front and the unstable detonation. Eventually, the unstable distorted detonation evolves into a spinning detonation.     

Three-dimensional cellular structure of detonations in suspensions of aluminium particles

Recently, we have used scarce available data on the detonation cell size in suspensions of aluminium particles in air and oxygen to adjust the kinetic parameters of our two-phase model of detonations in these mixtures. The calculated detonation cell width was derived by means of two-dimensional (2D) unsteady simulations using an assumption of cylindrical symmetry of the flow in the tube. However, in reality, the detonation cells are three-dimensional (3D). In this work, we have applied the same detonation model which is based on the continuous mechanics of two-phase flows, for 3D numerical simulations of cellular detonation structures in aluminium particle suspensions in oxygen. Reasonable agreement on the detonation cell width was obtained with the aforementioned 2D results. The range of tube diameters where detonations in $\text{ Al/O}_2$ mixture at a given particle size and concentration would propagate in the spinning mode has been estimated (these results make a complement to our previous analysis of spinning detonations in Al/air mixtures). Coupling these results with the dependencies of detonation cell size on the mean particle diameter is of great interest for the understanding of fundamental mechanisms of detonation propagation in solid particle suspensions in gas and can help to better guide the experimental studies of detonations in aluminium suspensions. It is shown that the part of detonation wave energy used for transverse kinetic energy of both gas and particles is quite small, which explains why the propagation velocity of spinning and multi-headed detonations reasonably agrees with the ideal CJ values.     

CH4-O2 混合气中爆燃爆震转捩的数值模拟

运用化学流体力学基本理论和两步燃烧反应模型原理，建立了一维封闭体系可燃气爆燃爆震转变现象的数学模型，利用拉格朗日质量坐标变换下的Ｌａｘ－Ｗｅｎｄｒｏｆ和Ｍｅｃｏｒｍｉｃ气动差分与Ａｄａｍｓ化学差分格式，求解基本方程，成功地完成了过程的数值模拟，清楚地说明了可燃气中ＤＤＴ现象由压缩波到激波达到稳态爆震的发生机制和火焰带引生爆震波的过程行为。     

A numerical simulation of reflection processes of a detonation wave on a wedge

Abstract. A two dimensional numerical simulation has been performed to study reflection processes of detonation waves on a wedge. The numerical scheme adopted is the flux corrected transport scheme and a two-step chemical reaction is assumed for a stoichiometric oxyhydrogen mixture diluted with argon. Transverse wave structures of the detonation are produced by artificial disturbances situated in front of a one-dimensional Chapman-Jouguet detonation wave. Numerical grids are generated by solving a Laplace equation. Results show that in the case where Mach reflection occurs, the cells in the Mach stem are smaller than those in the incident wave and are distorted in shape. There is also an initiating stage during which the cells in the Mach stem are created. The critical angle beyond which Mach reflection cannot occur is discussed. Received 15 October 1999 / Accepted 27 March 2000