Ideal gas flow behind a finite-amplitude shock wave

The equations of one-dimensional (with a plane of symmetry) adiabatic motion of an ideal gas are transformed to a form convenient for studying flows between a moving piston and a shock wave of variable intensity. The solution is found for the equations of a motion containing a shock wave which propagates through a quiescent gas with variable initial density and constant pressure. This solution contains four arbitrary constants and, in a particular case, gives an example of adiabatic shockless compression by a piston of a gas initially at rest.     

Pressure waves in a separated gas-liquid layer in a horizontal duct with a step

Pressure wave propagation into a separated gas-liquid layer in a horizontal duct with a step is investigated analytically. The linear solution is derived assuming a large density ratio of liquid to gas. The solution can be found first for the gas layer and then for the liquid layer. The linear wave in a liquid layer is valid even for fairly large initial pressure ratios, and clearly exhibits the dispersive characteristics of the pressure wave in a liquid layer. As the initial pressure ratio is increased, the pressure wave in the gas layer becomes a shock wave. Thus, its effect on the wave in a liquid layer can be found analytically by modifying the boundary condition in part. The wave in a liquid layer consists of a main wave, which propagates with the shock speed in gas, and a precursor wave, whose front propagates with the speed of sound in liquid. The precursor wave has an oscillatory structure; its amplitude increases with increasing shock strength and also with liquid layer thickness.     

Dynamic characteristics of spherically converging detonation waves

The spherically converging detonation wave was numerically investigated by solving the one-dimensional multi-component Euler equations in spherical coordinates with a dispersion-controlled dissipative scheme. Finite rate and detailed chemical reaction models were used and numerical solutions were obtained for both a spherical by converging detonation in a stoichiometric hydrogen-oxygen mixture and a spherically focusing shock in air. The results showed that the post-shock pressure approximately arises to the same amplitude in vicinity of the focal point for the two cases, but the post-shock temperature level mainly depends on chemical reactions and molecular dissociations of a gas mixture. While the chemical reaction heat plays an important role in the early stage of detonation wave propagation, gas dissociations dramatically affect the post-shock flow states near the focal point. The maximum pressure and temperature, non-dimensionalized by their initial value, are approximately scaled to the propagation radius over the initial detonation diameter. The post-shock pressure is proportional to the initial pressure of the detonable mixture, and the post-shock temperature is also increased with the initial pressure, but in a much lower rate than that of the post-shock pressure. Zonglin Jiang is presently a visiting professor at McGill University, Canada.     

氢氧燃烧及爆轰驱动激波管

分析并观察了沿驱动段轴向分布多火塞燃烧驱动段的性能．提出主膜处同一管截面均匀分布三火花塞引燃的点火方法．用这种点火方法驱动产生的入射激波强度重复性较高,激波后气流速度、温度和压力的定常性亦大大改善,可满足气动试验实际要求．提出在驱动段尾端串接卸爆段来消除爆轰波反射高压,从而可使反向爆轰驱动段用来产生高焓高密度试验气流．这种反向爆轰驱动产生的入射激波重复性高,激波衰减弱．在主膜处的收缩段产生的反射波可缓解爆轰波后跟随的稀疏波的不利影响,从而使前向爆轰驱动具有实用性．在产生的入射激波强度相同条件下,前向爆轰驱动所需的爆轰驱动段可爆混合气初始压力可较反向爆轰低近一个量级．     

Enhancement of shock waves

The flow field developed behind a shock wave propagating inside a constant cross-section conduit is solved numerically for two different cases. First, when the density of the ambient gas into which the shock propagates has a logarithmic change with distance. In the second, and the more practical case, the ambient gas is composed of pairs of air–helium layers having a continually decreasing width. It is shown that in both cases meaningful pressure amplification can be reached behind the transmitted shock wave. It is especially so in the second case. By proper choice of the number of air–helium layers and their width reduction ratio, pressure amplification as high as 7.5 can be obtained.      

Super-spherical cumulation: shock collapse which is more intense than the spherical one

A shock wave implosion in an axisymmetric chamber with a convex bounding wall is studied experimentally, analytically and numerically. The converging shock front area in this geometry shrinks quickly as the shock wave approaches the center point. The analytical theory predicts that the corresponding rate of post-shock pressure and density increase in this case exceeds essentially that achieved in the classical cylindrical or spherical shock implosions, hence, the phenomenon is referred to as “super-spherical cumulation”. The experiments confirm higher intensity of the super-spherical implosion compared with the cylindrical one, both driven by identical high-current pulsed electric discharges. The converging shock stability is analyzed in the framework of the CCW theory. The numerical results obtained using a locally-adaptive unstructured grid technique agree well with the theoretical predictions of the converging shock wave intensity. Received 28 January 1998 / Accepted 6 November 1998     

柱形汇聚激波冲击球形重气体界面的实验研究

采用高速纹影法实验研究了柱形汇聚激波与球形重气体界面相互作用的 Richtmyer-Meshkov不稳定性问题. 激波管实验段基于激波动力学理论设计, 将马赫数为1.2 的平面激波转化为柱形汇聚激波, 气体界面由肥皂膜分隔六氟化硫(内)和空气(外)得到. 采用高速摄影机在单次实验中拍摄激波运动的全过程, 对柱形激波的形成进行了实验验证, 并进一步观测了汇聚激波与球形气体界面相互作用过程中的波系发展和气体界面变形以及反射激波同已变形界面二次作用的流场演化. 结果表明: 当柱形汇聚激波穿过气泡界面以后, 气泡左侧界面极点沿激波传播方向保持匀速运动, 气泡右侧界面发展成为射流结构, 气泡主体发展成为涡环结构; 在反射激波的二次作用下, 流场中无序运动显著增强并很快进入湍流混合阶段.     

颗粒材料中致密波结构研究

采用一维两相流模型与相应颗粒构形应力函数,研究了致密波的形成及其结构．用简化两相流模型系统地讨论致密波对有关因素的依赖关系．分析指出：小于基体材料音速的致密波仅能在非理想颗粒材料中存在,从波前到波后,所有状态物理量光滑过渡．大于基体材料音速的致密波,波头可能存在间断．应力函数与致密粘性确定后,致密波速度决定致密波结构、宽度、终态压实度．采用一维两相流模型模拟了活塞驱动颗粒床形成致密波这一动态过程．用线方法（MOL）对该方程组求数值解．计算表明,经过短暂的非稳态过程,颗粒床中形成一稳态致密波．分析了活塞速度与初始孔隙率对致密波结构的影响,并对简化两相流模型与两相流模型的计算结果进行了对比．     

脉冲激光与正激波相互作用过程和减阻机理的实验研究

纳秒脉冲激光具有峰值功率密度高、易于击穿空气形成等离子体这一突出优势,在降低超声速波阻方面具有重要应用价值.以深刻揭示减阻机理为目的,针对激光与正激波相互作用这一基本物理现象开展实验研究.发展高精度纹影技术以测量复杂激波结构,时间分辨率达到 30ns,空间分辨率达到 1mm;搭建快速~PIV 实验系统以定量测量流场速度和涡量,时间分辨率达到 500ns.探明了激光等离子体引致的球面激波和高温低密度区域特性,揭示了激光等离子体在正激波冲击下的流动特性与演化规律,并结合数值模拟结果阐明了脉冲激光等离子体降低超声速波阻的根本原因.研究表明:激光等离子体引致激波的初始马赫数随着激光能量而增大,形状由水滴形逐渐发展为球面形,传播速度随着时间降低,在50$\mu$s 后接近于声速;高温低密度区域初始近似于球形,而后从激光入射方向的下游开始失稳,形成尖刺结构;在正激波冲击下,高温低密度区域演化为上下对称的双涡环结构,尺寸随着激光能量而增大.涡的卷吸和逆流可改变飞行器头部激波结构,是流场重构的重要形式,引起飞行器表面压力的大幅降低,是引起超声速飞行器波阻降低的重要机理.      

Appearance of Nucleation Shocks in a Boiling Liquid

Depressurization of high-pressure vessels filled with a liquid coming to the boil with a decrease in pressure is investigated. After depressurization, which takes less than 1 ms, a rarefaction wave propagates into the vessel. Experiments [1–5] demonstrated that the pressure behind the wave goes over to a constant value, which is independent of the vessel diameter and lies between the saturation point and atmospheric pressure.The correspondence between the experiments and different bubble formation theories (bubble formation on the vessel walls, due to rupture of the bonds between the water molecules or boiling on foreign particles) is analyzed. A “ mechanical nucleation” theory is proposed, in which it is assumed that the liquid comes to the boil on a limited number of foreign particles, and the bubbles formed on the nucleation centers undergo multiple fragmentation due to the instability developing under the action of centrifugal accelerations of the bubble surface in the course of bubble growth.The calculations demonstrated that, after depressurization, bubble fragmentation occurs at the vessel outlet. Due to the growth of the phase interface in the course of fragmentation, the boiling intensity increases, the pressure grows, and a shock wave propagates into the vessel, following the rarefaction wave. Multiple fragmentation of the bubbles occurs on the shock front. This wave is followed by a series of waves with smaller amplitudes. The pressure in the vessel attains a stable level, without any shocks. This level is characterized by the metastability or superheating of the liquid, i.e. the difference between the liquid temperature and the saturation point. It is demonstrated that the resultant pressure in the vessel is independent of the number of initial boiling centers or the initial pressure in the vessel and is determined only by the initial temperature. For water, the dependence of the superheating of the liquid on the initial temperature is found and compared with experimental data.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, 2005, pp. 103–117.Original Russian Text Copyright © 2005 by Ivashnev and Smirnov.     

Stability of converging cylindrical shock waves

An experimental and numerical study was made of converging cylindrical shock waves. The goal of the present study was to clarify the movement and instability of the converging cylindrical shock waves. Experiments were conducted in an annular shock tube of 230 mm o.d. and 210 mm i.d. connected to a cylindrical test section of 210 mm diameter. Double exposure holographic interferometry was used to visualize the converging cylindrical shock waves. Incident shock Mach numbers ranged between 1.1 and 2.0 in air. A numerical simulation was conducted using the TVD finite difference scheme. It was found in the experiments that although the initial shock wave configuration looked cylindrical, it was gradually deformed with propagation towards the center and finally showed mode-four instability. This is attributable to the existence of initial disturbances which were introduced by the struts which supported the inner tube of the annular shock tube. This trend was significant for stronger shock waves indicating that at the last stage of shock wave convergence the initial perturbations of the converging cylindrical shock wave were amplified to form the triple point of Mach reflection. The numerical results correctly predicted the experimental trend.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1990.     

弹体超高速侵彻石灰岩靶体地冲击的数值模拟研究

为探究超高速动能武器的对地破坏效应及其影响因素,采用数值模拟方法对弹体超高速侵彻的地冲击规律进行了研究。首先,基于石灰岩静动态力学性能实验数据对材料模型参数进行了标定,并对已有弹体大范围着速侵彻石灰岩靶体进行了模拟,验证了所采用材料模型和数值模拟方法的合理性。随后,开展了钨合金长杆弹超高速侵彻石灰岩靶体的数值模拟,细致分析了地冲击传播的现象和机理:弹体超高速侵彻靶体时,弹靶交界面处会产生瞬时高压,并以应力波的形式在靶体中传播,对靶体内部造成破坏,且当弹体初速度高于3.0 km/s时,地冲击显著增强。最后,进一步研究了不同弹靶参数对地冲击的影响,发现从相对深度来看,弹体参数（弹体长径比、密度）对地冲击规律影响不大;而靶体特征特别是孔隙率对地冲击传播具有较大影响。     

Mass,momentum and total excess energy transported by a weak planeN wave

A weakly nonlinear plane acoustic wave is emitted into an ideal gas of semi-infinite extent from an infinite plate by its sinusoidal motion of single period. The wave develops into anN wave in the far field, as long as the energy dissipation is negligible everywhere except for discontinuous shock fronts. The third-order effects at shock fronts are evaluated, i.e., the generation of reflected acoustic wave as a result of the interaction of shock and expansion wave and the production of entropy by the energy dissipation at shock fronts. Consideration of these effects enables one to estimate the whole mass, momentum and total excess energy (sum of the kinetic energy and excess of internal energy over an initial undisturbed value) transported by theN wave to the accuracy of third order of wave amplitude. It is shown that the mass and total excess energy transported by theN wave increase and the momentum decreases to asymptotic limits as the wave propagates. The result shows good agreement with a numerical result obtained by solving the Euler equations with a high-resolution TVD upwind scheme.     

气相爆轰波正反射激波加速研究

实验采用压力传感器测量了指定点压力时间曲线。数值模拟基于二维反应欧拉方程和基元反应模型,采用二阶附加半隐的龙格-库塔法和5阶WENO格式分别离散时间和空间导数项,获得了指定点数值压力时间曲线。理论分析基于爆轰理论和激波动力学,分析了气相爆轰波反射过程所涉及的复杂波系演变并获得了反射激波速度。结果表明:本文数值模拟和理论计算定性上重复并解释了实验现象。气相爆轰波在右壁面反射后,右行稀疏波加速反射激波。其加速原因是:尽管激波波前声速减小,但激波马赫数增大,波前气流速度减小。在低初压下,可能还由于爆轰波后未反应或部分反应气体的作用,导致反射激波加速幅度比高初压下大。     

准球面冲击波高压回收装置的研究

研究了以硝基甲烷液体炸药作为冲击波发生源的准球面汇聚冲击波超高压回收装置。在该装置上 ,利用冲击波由金属球体表面向中心汇聚形成的高压 ,对样品进行了冲击处理 ;分析了回收的金属球体内、外破坏情况及金相组织变化。结果表明 :该装置产生的球面冲击波对称性较好 ,样品回收可靠性较高 ;金属球体中心附近压力超过 2 0 7GPa ;对进行超高压冲击条件下的材料回收实验有较高的实用价值。     

Shock-wave-initiated lifting of particles from a cavity

The dynamics of particles of the disperse phase in a turbulent gas flow in planar shock waves sliding along a solid surface with a trapezoid cavity is examined numerically. Lifting of particles from the cavity walls is calculated in the approximation of a rarefied gas suspension. It is shown that the intensity of the transient shock wave and the initial positions of particles have a significant effect on the particle-lifting properties. The height of particle lifting is found to nonmonotonically depend on the initial streamwise coordinate and shock-wave Mach number. It is shown that zones of aggregation and subtraction of particles may be formed at the cavity bottom. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 1, pp. 24–34, January–February, 2007.     

激波的传播与干扰

激波的传播特性既取决于激波的产生条件,也与所处的传播环境密切相关。驱动条件、几何边界、介质的物理化学属性等发生变化时,都会引起激波传播特性的改变,而激波的变化反过来又会对其波及的流场产生影响。尽管激波传播及其干扰现象广泛存在于自然界和人类科技活动之中,其复杂机理的认识、规律的描述乃至应用潜力的挖掘仍有漫长的路要走。本文根据气体中激波传播和干扰现象以及与之相关的理论描述特征,在对激波传播以及反射、折射等基本现象进行简要阐述的基础上,重点围绕目前的热点问题,包括激波/激波干扰、激波/边界层干扰、激波与湍流作用、激波的聚焦与点火以及激波作用下气体界面不稳定性等研究进行了介绍和讨论,旨在对近年来该领域的进展及获得的成果做一个概述和归纳,期望对将来的深入研究有一个鉴借意义。     

流动肥皂膜气体界面及其在柱状汇聚激波作用下演化的实验研究

在Richtmyer-Meshkov(RM)不稳定性实验研究中,形成两种不同密度流体的初始扰动界面是前提和关健.本文提出了一种流动肥皂膜气体界面生成方法,其工作原理是由细丝构成的导流框从激波管实验段穿过,肥皂液从导流框的上端注入并在重力作用下在导流框中形成流动肥皂膜,膜的两测可以分别充入不同密度的气体从而形成稳定的气体...     

Impact on the surface of a compressible liquid

The evolution of a weak, nearly plane shock wave produced by the impact on the plane boundary of a compressible liquid is considered. At the initial moment the liquid is at rest and occupies the lower half-plane. Then the points of its boundary get instantly velocities directed into the liquid domain. This leads to the formation of a shock wave the intensity of which is non-uniform due to a non-uniform distribution of the impact velocities. Initially the shock wave is plane but then it bends due to the non-linear effects and can later be focused. To analyze the liquid flow, the method of matched asymptotic expansions is used. For finite times the flow and the evolution of the shock wave are described within the framework of the acoustic approximation. For large times the flow becomes non-linear, and the form of the shock front depends essentially on the characteristics of the liquid flow behind it. If the non-uniformity of the impact velocity distribution is slight then the focusing of the shock wave is shown not to occur. The influence of viscosity of the liquid on the structure of its motion is discussed.     

Characteristics of an annular vertical diaphragmless shock tube

Abstract. This paper reports on the characteristics of a compact vertical diaphragmless shock tube, which was constructed and tested in the Shock Wave Research Center to study experimentally the behavior of toroidal shock waves. It is 1.15 m in height and has a self-sustained co-axial vertical structure consisting of a 100 mm i.d. outer tube and an 80 mm o.d. inner tube. To create a ring shaped shock wave between the inner and outer tubes, a rubber sheet is inserted to separate a high pressure driver gas from a test gas, which is bulged with auxiliary high pressure helium from the behind. When the rubber membrane is contracted by the sudden release of the auxiliary gas so as to break the seal, shock waves are formed. Special design features of the shock tube are described and their role in producing repeatable shock waves is discussed. Its special opening characteristics make possible the production of annular shaped shock waves that are unlikely met with a conventional tube that uses rupturing diaphragms. Performance of the shock tube is evaluated in terms of the shock wave Mach numbers and the measured flow properties. It eventually showed a higher degree of repeatability and the scatter in the shock wave Mach numbers Ms was found to be 0.2% for Ms ranging from 1.1 to 1.8. The shock wave Mach number so far measured agreed very well with the simple shock tube theory. Received 3 February 1999 / Accepted 6 April 2000