Numerical investigations of shock waves in gas-particle mixtures

The propagation of shock waves in gas-particle mixtures in one- and two-dimensional geometries is numerically investigated. Two schemes for approximating conservation laws for particles, which are collectively treated as a continuum medium, are compared and discussed. Different models of the drag coefficient and Nusselt number, directly affecting the interaction between the gas and particle phases, are used for obtaining shock profiles, and the results are compared. The oblique shock reflections at a solid wedge in a gas-particle mixture are simulated. The results demonstrate that the reflection pattern changes as the shock propagates along the wedge, revealing strong non-selfsimilarity of the phenomenon.Received: 22 May 2003, Accepted: 28 August 2003, Published online: 12 November 2003 Correspondence to:T. Saito     

Specific gasdynamical features of spontaneous condensation in an unsteady rarefaction wave

On the basis of numerical modeling, the formation of an unsteady shock wave induced by a condensation shock in a rarefaction wave moving in the high-pressure channel of a shock tube filled with moist air is demonstrated. It is shown that in a fairly long channel a periodic structure consisting of an alternating sequence of condensation shocks and the shock waves they generate may be formed. This structure is a linear unsteady analog of the self-oscillation regime of type IV in the classification [1] for condensing medium flows in the subsonic section of a Laval nozzle. The specific features detected are important for planning and interpreting experiments aimed at investigating spontaneous condensation using a “condensation shock tube”.     

Theoretical analysis of acoustic instability of a hypersonic shock layer on a porous wall

The possibility of controlling the laminar-turbulent transition in hypersonic shock layers by means of porous coatings is considered. The linear stability of the shock layer to acoustic disturbances is analyzed. A dispersion relation is derived in an analytical form and analyzed for different characteristic values of porosity of the wall, which allows one to study the spectrum of acoustic disturbances in the shock layer. Analytical expressions for the growth rate of instability of acoustic disturbances are presented as functions of the reflection factor. Their structure indicates that the porous coating effectively decreases acoustic instability of the shock layer.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 1, pp. 44–54, January–February, 2005.     

Transient thermal stresses in an orthotropic hollow cylinder for axisymmetric problems

For the thermoelastic dynamic axisymmetric problem of a finite orthotropic hollow cylinder, one comes closer to reality to involve the effect of axial strain than to consider the plane strain case only. However, additional mathematical difficulties should be encountered and a different solution procedure should be developed. By the separation of variables, the thermoelastic axisymmetric dynamic problem of an orthotropic hollow cylinder taking account of the axial strain is transformed to a Volterra integral equation of the second kind for a function of time, which can be solved efficiently and quickly by the interpolation method. The solutions of displacements and stresses are obtained. It is noted that the present method is suitable for an orthotropic hollow cylinder with an arbitrary thickness subjected to arbitrary axisymmetric thermal loads. Numerical comparison is made to show the effect of the axial strain on the displacements and stresses. The project supported by the National Natural Science Foundation of China (10172075) and China Postdoctoral Science Foundation (20040350712)     

高超声速钝锥流场红外辐射实验研究

报道了在JF-10氢氧爆轰驱动高焓激波风洞中开展的再入流场红外辐射实验研究. 风洞的试 验状态为：驻室总压19.6MPa, 总焓15.5MJ/kg, 自由流速度约5 km/s. 实验以锑化铟多元红外成像系统为测量手段，以球头钝锥体为试验模型，测量激波层与近尾流中红外辐射功率 的横向分布剖面. 试验数据呈现明显的规律性. 试验结果表明，激波层内壁面附近的红外辐 射功率较小，中间有一区域辐射较大且相对均匀，激波层外缘辐射单调减小；尾流中红外辐 射功率在轴线附近的核心区最大，随着离轴线距离的增大而单调减小.     

Multiple pulsed hypersonic liquid diesel fuel jetsdriven by projectile impact

Further studies on high-speed liquid diesel fuel jets injected into ambient air conditions have been carried out. Projectile impact has been used as the driving mechanism. A vertical two-stage light gas gun was used as a launcher to provide the high-speed impact. This paper describes the experimental technique and visualization methods that provided a rapid series of jet images in the one shot. A high-speed video camera (10⁶ fps) and shadowgraph optical system were used to obtain visualization. Very interesting and unique phenomena have been discovered and confirmed in this study. These are that multiple high frequency jet pulses are generated within the duration of a single shot impact. The associated multiple jet shock waves have been clearly captured. This characteristic consistently occurs with the smaller conical angle, straight cone nozzles but not with those with a very wide cone angle or curved nozzle profile. An instantaneous jet tip velocity of 2680 m/s (Mach number of 7.86) was the maximum obtained with the 40 nozzle. However, this jet tip velocity can only be sustained for a few microseconds as attenuation is very rapid.Received: 13 December 2003, Accepted: 11 April 2004, Published online: 11 February 2005[/PUBLISHED]K. Pianthong: Correspondence to:      

BUFFER AND COMPLIANT DYNAMIC SURFACE CONTROL OF SPACE ROBOT CAPTURING SATELLITE BASED ON COMPLIANT MECHANISM$^{\bf 1)}$

研究了空间机器人在轨捕获非合作卫星过程避免关节受碰撞冲击破坏的缓冲从顺控制问题, 为此在机械臂与关节电机之间配置了一种柔性机构, 其作用在于: (1)在接触、碰撞阶段可通过其内置弹簧的变形来吸收被捕获卫星对空间机器人关节产生的冲击力矩; (2)在镇定运动阶段, 结合与之配合的缓冲从顺控制策略来适时开、关关节电机, 以保证关节受到的冲击力矩受限在安全范围. 首先, 利用多刚体系统理论获得配置柔性机构空间机器人及目标卫星分体系统动力学方程; 之后, 结合整个系统动量守恒关系, 捕获操作后系统运动几何关系及力的传递规律, 建立了两者形成联合体系统的动力学方程, 并计算了碰撞过程的冲击效应与冲击力. 为了实现失稳联合体系统的镇定控制, 提出了一种基于动态面的缓冲从顺控制方案. 上述控制方案可在实现吸收捕获操作产生的冲击力矩的同时, 还能在冲击力矩过大时适时开启、关闭关节电机, 以避免关节电机发生破坏; 此外, 动态面的引入避免了反演法存在的计算膨胀问题, 有效减少了计算量. 基于Lyapunov函数法证明了系统的稳定性, 并通过系统数值仿真结果验证了上述缓冲从顺控制策略的正确性.     

Measurement of Reflected-shock Bifurcation Over a Wide Range of Gas Composition and Pressure

To determine the extent and magnitude of reflected-shock bifurcation in shock-tube chemistry studies at elevated pressures, experiments were performed using a simple laser schlieren technique and a fast- response pressure transducer. The laser schlieren diagnostic provided a quantitative measurement of the normal-shock passage, an event normally obscured in pressure signals by the bifurcated region. A range of gas mixtures covering molecular weights from 14.7 to 44.0 and specific heat ratios from 1.29 to 1.51 was explored. The results were combined with a standard gas dynamic model to determine the time of arrival of the normal shock wave, the size and strength of the bifurcated region, and the characteristic passage times of dominant features. All results could be expressed in empirical correlations as functions of the gas properties and shock speed. The measured size of the bifurcation zone increased with increasing shock velocity and decreasing specific heat ratio, but displayed no pressure dependence for the conditions of this study (P ₅ = 11 − 265 atm., T ₅ = 780 − 1740 K).     

坑道内化爆冲击波的传播规律

装药在坑道内部爆炸时将产生沿坑道传播的空气冲击波,由于受到坑道洞壁的限制,空气冲击波在坑道内的传播规律异于在自由大气中的传播。利用三维数值模拟计算程序,对长坑道中的化爆流场进行了数值计算,归纳出空气冲击波沿坑道方向的传播规律。计算结果与试验结果符合较好。