爆轰波通过扩张喷管的双曝光全息实验和数值研究

结合实验和数值模拟方法,对以脉冲爆轰发动机为背景的爆轰波通过扩张喷管的流动进行了系列研究。实验采用双曝光全息干涉方法对爆轰波绕射流场进行测量,得到了比传统的纹影法更清晰和可定量化的照片。发展了基于非结构四边形网格自适应有限体积程序,结合基元化学反应模型对扩张喷管中爆轰化学反应流场进行了数值模拟,模拟结果与实验照片吻合较好。实验和数值模拟结果表明,爆轰波绕射具有许多和激波绕射不同的流场特征,其中包括二次起爆现象、化学反应面与前导激波相脱离而引起的复杂流场等,同时初始压力和扩张角度变化也对爆轰波绕射过程产生较大影响,初始压力越低,化学反应区和前导激波分离现象越明显,且前导激波的曲率越大。     

煤油液滴直径对两相旋转爆轰发动机流场的影响

为探究煤油液滴不同初始直径对气液两相旋转爆轰发动机流场的影响，假设初始注入的煤油液滴具有均匀直径，考虑雾化破碎、蒸发等过程，建立了非定常两相爆轰的Eulerian-Lagrangian模型，进行了液态煤油/高温空气爆轰的非预混二维数值模拟。结果表明：在初始液滴直径为1～70μm的工况范围，燃烧室内均形成了单个稳定传播的旋转爆轰波；全局当量比为1时，爆轰波前的空气区域大于液滴煤油的蒸气区域，导致波前燃料空气混合不均匀，波前均存在富油区和贫油区，两相速度差导致分离出的空气形成低温条带；当煤油液滴的初始直径较小时，波前的反应物混合过程主要受蒸发的影响，爆轰波可稳定传播；当直径减小至1μm时，煤油液滴在入口处即蒸发，旋转爆轰波表现为气相传播的特性，爆轰波结构平整；当煤油液滴的初始直径较大时，波前的反应物混合过程主要受液滴破碎的影响；对于相同的燃料质量流量，在不同初始煤油液滴直径工况下，煤油液滴最大的停留时间均占爆轰波传播时间尺度的80%以上；爆轰波前燃料预蒸发为气相的占比越高，爆轰波的传播速度越高；初始液滴直径为10～70μm的工况范围内，爆轰波的速度随初始直径的增大先升高后降低。     

气相爆轰波传播过程中的自点火效应

基于基元反应模型和单步反应模型，对直管道中H₂-air混合气体中爆轰波的传播过程进行了数值模拟，揭示了气相爆轰波传播过程中的自点火效应。利用数值模拟方法计算了不同爆轰模型的点火延迟时间，并得到了爆轰波三波点的传播过程以及所形成胞格结构的尺寸。结果表明，胞格宽度与点火延迟时间成正比；爆轰波诱导区内气体的点火延迟时间与三波点的运动周期基本一致。进一步对结果分析可知，爆轰波的自维持传播取决于点火延迟时间(表征化学反应的特征时间)和三波点的运动周期(表征流动的特征时间)的匹配；当二者相匹配时，经过前导激波压缩后形成的高温高压爆轰气体，在短时间内实现了自点火，同时释放出大量的能量推动了爆轰波的前进，即爆轰波的稳定自维持传播依靠其自点火机制。     

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.     

立式激波管内云雾爆轰胞格尺寸的测定与分析

采用烟迹技术在立式激波管中测定了环氧丙烷、90#汽油、硝酸异丙酯、庚烷、癸烷、戊二烯等几种燃料气液两相云雾爆轰的胞格尺寸。结果表明,云雾爆轰的胞格尺寸随当量比的变化呈U形曲线关系,且最小胞格尺寸并不是对应于等化学当量比而是偏向于富燃料一侧,这与气相爆轰的结论是一致的。胞格尺寸随起爆能的增加而减小。当起爆能达到一定值后,胞格尺寸变化不明显,若起爆能继续增加,在通常的胞格内出现精细结构。云雾爆轰波胞格长度与宽度的比值比气相爆轰小。另外,根据烟迹记录分析了云雾爆轰作用机制,认为液滴的碎解、汽化过程以及燃烧区前导是控制气液两相云雾爆轰的主要因素。     

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。     

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.     

气云爆轰的一维模型

激波作用下，悬浮液谪在高温、高压和高速气流中变形、蒸发、剥离甚至破碎。雾化燃料经过一段延迟时间后点火燃烧释放出大量的能量。这些能量由局部爆炸波所携带，通过碰撞传递给引导微波，从而使气云爆轰波自持。文中提出的气云爆轰的一维模型考虑了上述基本过程，并从理论上推导了点火面和ＣＪ面的判据。通过计算，文中讨论了气云爆轰的松弛结构和影响ＣＪ爆速的因素，爆速的计算值与实验值基本相符。     

超音速来流中爆轰波衍射和二次起爆过程研究

预爆管技术被广泛地应用在爆轰波发动机的起爆过程中，但是在超音速来流中基于预爆管技术起始爆轰波的研究并未被广泛地开展。基于此，本文中数值研究了横向超音速来流对半自由空间内爆轰波的衍射和自发二次起爆、及管道内的衍射和壁面反射二次起爆两种现象的影响。数值模拟的控制方程为二维欧拉方程，空间上使用五阶WENO格式进行数值离散，采用带有诱导步的两步链分支化学反应模型。所模拟的爆轰波具有规则的胞格结构，对应于用惰性气体高度稀释过的可爆混合物中形成的爆轰波。结果表明:在半自由空间内，在本文所模拟的几何尺寸下，爆轰波并未成功发生二次起爆现象，但是爆轰波的自持传播距离随着横向超音速来流强度的增强而增加。在核心的三角形流动区域外，波面诱导产生了更多的横波结构；在管道内，横向的超音速来流在逆流侧对出口气流产生了压缩作用，能有效提高波面压力，因此反射后的激波压力也比较高。在同样的几何尺寸下，爆轰波在静止和超音速(Ma=2.0)气流中分别出现了二次起爆失败和成功两种现象，这是由于在超音速来流中化学反应面的褶皱诱导产生了横波结构，横波与管壁以及其他横波之间的碰撞提高了前导激波的强度，并最终促进了爆轰波在超声速流主管道内的成功起始。     

液体碳氢燃料云雾爆轰特性的实验研究

采用升降法和烟迹技术在立式激波管中分别实测了液态燃料（环氧丙烷、硝酸异丙酯、己烷、C5~C6、庚烷、癸烷）与空气混合物直接起爆的临界起爆能和胞格尺寸。数据表明,气液两相云雾爆轰的临界起爆能与当量比呈U形曲线关系,这与气相爆轰得到的结论是一致的;临界起爆能的最小值并不是对应于等化学当量的混合物而是偏向于富燃料;根据三波点运动的烟迹记录,分析了云雾爆轰作用机制,认为液滴的碎解、汽化过程以及燃烧区前导是控制气液两相云雾爆轰的主要步骤。此外,还测定了无限空间下可燃气云的临界起爆能,并将激波管内得到的临界起爆能数据外推到无约束气云的临界起爆能,理论推算结果与实验值吻合较好。     

Head-on Collision of a Detonation with a Planar Shock Wave

The phenomenon that occurs when a Chapman–Jouguet (CJ) detonation collides with a shock wave is discussed. Assuming a one-dimensional steady wave configuration analogous to a planar shock–shock frontal interaction, analytical solutions of the Rankine–Hugoniot relationships for the transmitted detonation and the transmitted shock are obtained by matching the pressure and particle velocity at the contact surface. The analytical results indicate that there exist three possible regions of solutions, i.e. the transmitted detonation can have either strong, weak or CJ solution, depending on the incident detonation and shock strengths. On the other hand, if we impose the transmitted detonation to have a CJ solution followed by a rarefaction fan, the boundary conditions are also satisfied at the contact surface. The existence of these multiple solutions is verified by an experimental investigation. It is found that the experimental results agree well with those predicted by the second wave interaction model and that the transmitted detonation is a CJ detonation. Unsteady numerical simulations of the reactive Euler equations with both simple one-step Arrhenius kinetic and chain-branching kinetic models are also carried out to look at the transient phenomena and at the influence of a finite reaction thickness of a detonation wave on the problem of head-on collision with a shock. From all the computational results, a relaxation process consisting of a quasi-steady period and an overshoot for the transmitted detonation subsequent to the head-on collisions can be observed, followed by the asymptotic decay to a CJ detonation as predicted theoretically. For unstable pulsating detonations, it is found that, due to the increase in the thermodynamic state of the reactive mixture caused by the shock, the transmitted pulsating detonation can become more stable with smaller amplitude and period oscillation. These observations are in good agreement with experimental evidence obtained from smoked foils where there is a significant decrease in the detonation cell size after a region of relaxation when the detonation collides head-on with a shock wave.     

Detonation in heterogeneous mixtures of liquids and particles

The mechanisms of detonation propagation in heterogeneous systems comprising closely packed particles and a liquid explosive are not fully understood. Recent experimental work has suggested the presence of two distinct modes of detonation propagation. One mode is valid for small particles (which is the regime we will address in this paper) with another mode for large particles. In this work we model numerically the detail of the wave interactions between the detonating liquid and the solid particles. The generic system of interest in our work is nitromethane and aluminium but our methodology can be applied to other liquids and particles. We have exercised our numerical models on the experiments described above. Our models can now qualitatively explain the observed variation in critical diameter with particle size. We also report some initial discrepancies in our predictions of wave speeds in nominally one dimensional experiments which can be explained by detailed modelling. We find that the complex wave interaction in the flow behind the leading shock in the detonating system of liquid and particles is characterised by at least two sonic points. The first is the standard CJ point in the reacting liquid. The second is a sonic point with respect to the sound speed in the inert material. This leads to a steady state zone in the flow behind the leading shock which is much longer than the reaction zone in the liquid alone. The width of this region scales linearly with particle size. Since the width of the subsonic region strongly influences the failure diameter we believe that this property of the flow is the origin of the observed increase in failure diameter with particle size for small inert particles. Received 3 December 1999 / Accepted 5 July 2000     

A numerical investigation of transient detonation in granulated material

A two-phase model based upon principles of continuum mixture theory is numerically solved to predict the evolution of detonation in a granulated reactive material. Shock to detonation transition (SDT) is considered whereby combustion is initiated due to compression of the material by a moving piston. In particular, this study demonstrates the existence of a SDT event which gives rise to a steady two-phase Chapman-Jouguet (CJ) detonation structure consisting of a single lead shock in the gas and an unshocked solid; this structure has previously been independently predicted by a steady-state theory. The unsteady model equations, which constitute a non-strictly hyperbolic system, are numerically solved using a modern high-resolution method. The numerical method is based on Godunov's method, and utilizes an approximate solution for the two-phase Riemann problem. Comparisons are made between numerical predictions and known theoretical results for 1) an inert two-phase shock tube problem, 2) an inert compaction wave structure, and 3) a reactive two-phase detonation structure; in all cases, good agreement exists. Received 4 August 1995 / Accepted 17 February 1996     

高速弹丸诱导斜爆轰激波结构实验研究

斜爆轰推进系统在高超声速推进领域具有广阔的应用前景,其释热迅速、比冲高、燃烧室结构简单的优点吸引研究人员的持续关注.然而,斜爆轰的地面试验同时涉及到高速试验环境模拟、燃料与氧化剂混合、高温燃烧流场结构测量等技术难点,当前国内外系统的试验研究仍然十分有限,难以支撑斜爆轰发动机的研制.为了研究自持传播的斜爆轰激波结构与波面流动特性,基于爆轰驱动二级轻气炮开展了高速弹丸诱导斜爆轰实验研究,使用直径30 mm球头圆柱形弹丸发射进入充满氢/氧可燃混合气体的实验舱中以起爆斜爆轰波,并采用两种阴影技术对实验流动结构进行测量.实验中在不同速度、不同充气压力下观察到三种弹丸诱导激波结构,即激波诱导燃烧、弹丸起爆爆轰波和相对弹丸驻定的斜爆轰波,实验舱充气压力下降则会造成爆轰横波尺度增加与波面流动失稳.实验中,斜爆轰激波角与理论分析结果吻合较好,弹丸气动不稳定带来较大的弹丸攻角会对激波角测量带来一定偏差.通过对斜爆轰波波面法向传播速度的测量发现,随着远离弹丸,斜爆轰传播速度由弹丸飞行速度衰减至接近实验气体CJ速度,弹丸速度的降低会加速斜爆轰波传播速度的衰减.     

Detonation diffraction in combustible high-speed flows

Detonation propagating in a T-shaped tube with quiescent and moving hydrogen/oxygen/argon mixtures is numerically examined based on the Euler equations with detailed finite-rate chemistry using the fifth-order weighted essentially non-oscillatory scheme. When diffracted in a quiescent combustible mixture, the detonation wave propagating from the bottom of the T-shaped tube is influenced by the corner rarefaction waves and decays into a non-reacting shock. Subsequently, the decoupled shock reflects irregularly from the top wall. Through several reflections back and forth between the top and bottom walls, a planar detonation is finally re-established. When the combustible mixture in the horizontal part flows from the left to the right, the detonation products ejected from the vertical tube will retard the flow, generating a compression flow upstream and a rarefaction flow downstream. The disturbed detonation on the left side is stronger than that on the right side. The final planar detonation in the upstream direction propagates faster than the Chapman–Jouguet (CJ) detonation with compressed, fine cellular structures, whereas the detonation in the downstream direction propagates more slowly than the CJ detonation with elongated, coarse cellular structures. The details of the transient behavior of diffracting detonation in high-speed flows are discussed.     

On the propagation mechanism of a detonation wave in a round tube with orifice plates

This study deals with the investigation of the detonation propagation mechanism in a circular tube with orifice plates. Experiments were performed with hydrogen air in a 10-cm-inner-diameter tube with the second half of the tube filled with equally spaced orifice plates. A self-sustained Chapman–Jouguet (CJ) detonation wave was initiated in the smooth first half of the tube and transmitted into the orifice-plate-laden second half of the tube. The details of the propagation were obtained using the soot-foil technique. Two types of foils were used between obstacles, a wall-foil placed on the tube wall, and a flat-foil (sooted on both sides) placed horizontally across the diameter of the tube. When placed after the first orifice plate, the flat foil shows symmetric detonation wave diffraction and failure, while the wall foil shows re-initiation via multiple local hot spots created when the decoupled shock wave interacts with the tube wall. At the end of the tube, where the detonation propagated at an average velocity much lower than the theoretical CJ value, the detonation propagation is much more asymmetric with only a few hot spots on the tube wall leading to local detonation initiation. Consecutive foils also show that the detonation structure changes after each obstacle interaction. For a mixture near the detonation propagation limit, detonation re-initiation occurs at a single wall hot spot producing a patch of small detonation cells. The local overdriven detonation wave is short lived, but is sufficient to keep the global explosion front propagating. Results associated with the effect of orifice plate blockage and spacing on the detonation propagation mechanism are also presented.     

可燃介质中飞行圆球诱导斜爆轰的流场结构

基于带化学反应的二维轴对称Euler方程,利用带有Superbee限制函数的波传播算法,对氢/氧/ 氮预混气中飞行圆球诱导斜爆轰进行了数值模拟。结果表明,在达姆科勒数Da略大于临界情形时,圆球诱导 的驻定爆轰是一个由强过驱斜爆轰、弱过驱斜爆轰、反应激波和惰性激波组合而成的复合结构。波后的圆球 绕流流场内存在2个亚音速区和1个超音速区。在圆球背风表面,还形成了第2道斜激波。     

含铝炸药能量释放的简化模型

为了在水下爆炸效应中反映出非理想爆轰特性的影响,建立了含铝炸药非理想爆轰能量释放的简化模型。该模型以CJ爆轰理论和二次反应理论为基础,把含铝炸药化学反应划分为快速反应和慢速反应,以释放的化学能和慢反应速率常数作为非理想特征参数,并应用于一维数值模拟。计算结果与基本实验结果一致,冲击波峰值的计算误差不大于10％,衰减时间常数的误差小于5％,冲击波能与实验值也具有良好的一致性。简化模型合理地描述了含铝炸药非理想爆轰的主要过程及非理想特性,可应用于含铝炸药的设计和爆炸效应的分析。