激波作用下水膜变形和雾化实验研究

在激波与液滴作用研究的基础上,开展了激波作用下水膜的变形和雾化过程研究。通过阴影照相技术捕捉激波与水膜作用的典型照片,并以此分析其作用机理。通过改变激波强度观察水膜的变形和雾化情况。研究发现激波强度越大,水膜雾化后抛撒的距离越远,证明气动力在作用过程中起主导作用。使用PDPA系统对抛撒后水雾粒子的直径和速度进行测量,结果发现激波作用后初期,气动力仍起着主导作用。     

冷激波灭火系统中激波对灭火效果和周边环境的影响

为了评估冷激波灭火弹爆炸后形成的激波对灭火效果和周边环境的影响,建立了一套纹影实验装置。通过纹影实验,观察了小尺寸下不同灭火介质爆炸抛撒后激波的形成和传播,并推算了冷激波灭火弹爆炸后油盆边缘附近的波后质点速度。观察发现,水基灭火介质爆炸抛撒后没有形成激波;而粉基灭火介质尽管爆炸抛撒后形成激波,但在油盆边缘附近激波强度较弱,波后质点速度小。与介质抛撒引起的可燃气体介质运动相比,激波对加快可燃气体介质运动的影响可以忽略。最后,通过高速摄影实验验证了激波对灭火效果的影响是可以忽略的。因此,冷激波系统中,激波对灭火效果和周边环境的影响是可以忽略的。     

激波作用下液体喷射雾化的实验研究

液体在气流作用下的喷射抛撒过程是流体力学研究中令人感兴趣的重要领域,笔者采用改进后的激波管实现了激波作用下液体的喷射抛撒,并通过阴影照相和激光散射法分别对液体的抛撒状态和抛撒液滴的直径进行了测量,研究表明,在喷射过程中,流场中固定位置所测得的液滴Ｓａｒｔｅｒ平均直径随时间的发展而逐渐减小,在开始时时刻液滴直三小较快而最终渐趋平缓;在对不同抛撒距离雾化场的测量中发现,没位置测得的颗粒最大直 隧测得位     

秦岭公路隧道2号竖井地应力与岩爆分析

利用水平圆柱形激波管对激波驱动的可压缩性气固两相流进行了试验研究. 利用压电式压力传感器、电荷放大器、示波器及计算机组成的压力信号测试系统, 对激波 与颗粒作用前后的气相参数进行测量及分析. 试验中测得了激波在管中的传播速 度, 波后气流的压力, 反射激波、透射激波的压力和速度等. 分别考察颗粒、装载 比、驱动气源以及入射激波马赫数等因素的差异对气相参数的影响. 试验结果表明: 激波与颗粒群相互作用时, 会产生反射激波和透射激波, 其强度与驱动气源、颗粒大小、颗粒装载比等参数有关; 激波衰减率随着装载比、马赫数的增大而减小. 研究指出, 在颗粒群被激波加速的初始阶段, 颗粒间的弹性碰撞起着重要的作用.     

激波驱动的气固两相流的动态压力测量

利用水平圆柱形激波管对激波驱动的可压缩性气固两相流进行了试验研究.利用压电式压力传感器、电荷放大器、示波器及计算机组成的压力信号测试系统, 对激波与颗粒作用前后的气相参数进行测量及分析. 试验中测得了激波在管中的传播速度, 波后气流的压力, 反射激波、透射激波的压力和速度等. 分别考察颗粒、装载比、驱动气源以及入射激波马赫数等因素的差异对气相参数的影响.试验结果表明: 激波与颗粒群相互作用时, 会产生反射激波和透射激波,其强度与驱动气源、颗粒大小、颗粒装载比等参数有关;激波衰减率随着装载比、马赫数的增大而减小. 研究指出,在颗粒群被激波加速的初始阶段, 颗粒间的弹性碰撞起着重要的作用.      

激波与可运动颗粒群相互作用反射与透射机理实验研究

对水平圆柱形激波管内可压缩性气体与颗粒群的相互作用进行了实验研究与理论分析。利用由压力传感器、信号放大器、示波器和计算机组成的压力测量系统对激波与颗粒群作用时的动态压力进行了测量。发现激波管内发生的是一个复杂的过程,包括激波与颗粒群作用时伴随了激波和膨胀波的反射与透射现象、激波和膨胀波与接触面的干涉、以及激波从激波管端壁的反射等现象。当颗粒装载比α=1时,透射激波被直径为6mm的颗粒群衍射并且有膨胀波紧随其后,因此由透射激波引起的第一个压力峰急剧下降。颗粒装载比和颗粒直径影响透射激波的衍射和衰减。     

固体颗粒对半球扰动尾迹影响的实验研究

采用粒子图像测速技术(particle image velocimetry, PIV)研究固体颗粒对放置在平板层流边界层中半球粗糙元尾迹的影响.实验采集了清水和加入粒径为140μm, 220μm, 350μm聚苯乙烯固体颗粒4种工况下二维速度场信息,基于半球半径的雷诺数为994 (Re_R=RU/υ),固体颗粒的体积浓度为3.0×10~(-5).对比清水和两相工况下的平均速度剖面、湍流强度等宏观统计量,分析固体颗粒对半球尾迹流动宏观特性的影响.分别利用沿流向不同位置的流向脉动速度的二维空间相关系数和法向脉动速度的功率谱密度函数分析颗粒对尾迹结构演化过程及尾迹结构脱落频率的影响.结果发现:与清水相比,回流区随颗粒粒径增大而逐渐增大;颗粒使湍流强度增大,回流区的存在导致在半球后流向位置2R前后区域湍流强度呈现不同变化趋势;颗粒使尾迹结构的流向尺度减小并且随着颗粒粒径的增大先减小后增大;在尾迹结构运动过程中颗粒的存在促进了尾迹结构的周期性加速和减速运动,促进作用随着颗粒粒径的增大先增强后减弱;颗粒的存在促进了尾迹结构的脱落,脱落频率随颗粒粒径的增大先增大后减小.     

运动状态下液体轴对称抛撒首次破碎的实验研究

在实验室条件下利用组合式激波管设备,对运动状态下液体轴对称抛撒进行了实验研究。通过纹影装置获得其所形成雾化场的外形轮廓照片,测量获得了液核发生首次破碎的位置与对称轴之间的距离。通过对抛撒过程中R-T不稳定性与K-H不稳定性的分析认为,轴向气流作用下液体轴对称抛撒的首次破碎点与对称轴的距离主要由轴向气流的速度、轴向气流的密度、液体轴对称抛撒的出口速度、抛撒液体的表面张力系数、环形喷口的宽度等参数所决定。在此基础上,利用相似性理论和无量纲分析,获得了运动状态下液体轴对称抛撒首次破碎点与对称轴之间的距离与相关参数的无量纲关系式。     

用激波管研究超音速气固两相流

在激波管里进行了可压缩性气固两相流的实验研究。测量了激波通过颗粒群时的压力的衰减过程。用纹影仪拍摄了激波与颗粒群相互干涉的照片。试验了颗粒群的不同构造对压力衰减的影响。指出了激波反射、聚焦等非线性气动因素是可压缩性气固两相流的关键问题。     

固体颗粒对半球扰动尾迹影响的实验研究

采用粒子图像测速技术(particle image velocimetry, PIV)研究固体颗粒对放置在平板层流边界层中半球粗糙元尾迹的影响. 实验采集了清水和加入粒径为140 $\mu$m, 220 $\mu$m, 350$\mu$m聚苯乙烯固体颗粒4种工况下二维速度场信息, 基于半球半径的雷诺数为994 ($Re_R=RU/\upsilon$), 固体颗粒的体积浓度为$3.0\times10^{-5}$. 对比清水和两相工况下的平均速度剖面、湍流强度等宏观统计量, 分析固体颗粒对半球尾迹流动宏观特性的影响. 分别利用沿流向不同位置的流向脉动速度的二维空间相关系数和法向脉动速度的功率谱密度函数分析颗粒对尾迹结构演化过程及尾迹结构脱落频率的影响. 结果发现: 与清水相比, 回流区随颗粒粒径增大而逐渐增大; 颗粒使湍流强度增大, 回流区的存在导致在半球后流向位置$2R$前后区域湍流强度呈现不同变化趋势; 颗粒使尾迹结构的流向尺度减小并且随着颗粒粒径的增大先减小后增大; 在尾迹结构运动过程中颗粒的存在促进了尾迹结构的周期性加速和减速运动, 促进作用随着颗粒粒径的增大先增强后减弱; 颗粒的存在促进了尾迹结构的脱落, 脱落频率随颗粒粒径的增大先增大后减小.      

Experimental study of planar shock wave interactions with dense packed sand wall

A dense packed sand wall is impacted by a planar shock wave in a horizontal shock tube to study the shock-sand wall interaction. The incident shock Mach number ranges from 2.18 to 2.38. A novel device for actively rupturing diaphragm is designed for the driver section of the shock tube. An apparatus for loading particles is machined by the electrical discharge cutting technique to create a dense packed particle wall. High-speed schlieren imaging system and synchronized pressure measurement system are used together to capture the wave structures and particle cloud velocity. The dynamic evolution model from dense packed particles to dense gas–solid cloud at the initial driving stage is established. The blockage and permeation effects of the sand wall work together and influence each other. The high pressure gas behind the incident shock wave blocked by the sand wall pushes the upstream front of the wall forward like a piston. Meanwhile, the high speed gas permeating through the sand wall drags the sands of the most downstream layer forward. The incident shock strength, initial sand wall thickness and particle diameter are varied respectively to investigate the shock attenuation and the wall acceleration. Increasing the sands diameter or mixing in small diameter sands can significantly attenuate the incident shock. The smaller particles or the particles in thinner wall can be dispersed into a larger range in the process of transform from dense packed particles to dense gas–solid cloud. Moreover, the stronger incident shock can disperse the particles into a larger region.     

Explosive dispersal of solid particles

Abstract. The rapid dispersal of inert solid particles due to the detonation of a heterogeneous explosive, consisting of a packed bed of steel beads saturated with a liquid explosive, has been investigated experimentally and numerically. Detonation of the spherical charge generates a blast wave followed by a complex supersonic gas-solid flow in which, in some cases, the beads catch up to and penetrate the leading shock front. The interplay between the particle dynamics and the blast wave propagation was investigated experimentally as a function of the particle size (100–925 m) and charge diameter (8.9–21.2 cm) with flash X-ray radiography and blast wave instrumentation. The flow topology during the dispersal process ranges from a dense granular flow to a dilute gas-solid flow. Difficulties in the modeling of the high-speed gas-solid flow are discussed, and a heuristic model for the equation of state for the solid flow is developed. This model is incorporated into the Eulerian two-phase fluid model of Baer and Nunziato (1986) and simulations are carried out. The results of this investigation indicate that the crossing of the particles through the shock front strongly depends on the charge geometry, the charge size and the material density of the particles. Moreover, there exists a particle size limit below which the particles cannot penetrate the shock for the range of charge sizes considered. Above this limit, the distance required for the particles to overtake the shock is not very sensitive to the particle size but remains sensitive to the particle material density. Overall, excellent agreement was observed between the experimental and computational results. Received 16 August 1999 / Accepted 26 June 2000     

On shock wave propagation in a branched channel with particles

The problem of wave propagation in a dust–air mixture inside a branched channel has not been studied widely in literature, even though this topic has many important applications especially in process safety (dust explosions). In this paper, a shock wave interaction with a cloud of solid particles, and the further behaviour of both gas and particulate phases were studied using numerical techniques. The geometry mimicked a real channel where bends or branches are common. Two numerical approaches were used: Eulerian–Eulerian and Eulerian–Lagrangian. Using Eulerian-Lagrangian simulation, it was possible to include the effects of particle–particle and particle–wall collisions in a realistic and direct manner. Results are mainly shown as snap-shots of particle positions during the simulations and statistics for the particle displacement. The results show that collisions significantly influence the process of particle cloud formation. PACS47.40.Nm, 02.60.Cb, 47.55.kf     

Interaction of a shock wave with a particle cloud of finite size

We present the results of the numerical modelling of the interaction of a shock wave with a cloud of finite size particles. The computations were carried out within the framework of continuum/discrete model with the use of the techniques of digital diagnostics and pattern recognition. The shock wave and vortex formation behind the cloud of particles as well as the formation of a dense layer in the cloud have been revealed. For this reason, the use of a cloud of particles for relaxing the shock wave may prove to be inefficient.     

Dense particle cloud dispersion by a shock wave

A dense particle flow is generated by the interaction of a shock wave with an initially stationary packed granular bed. High-speed particle dispersion research is motivated by the energy release enhancement of explosives containing solid particles. The initial packed granular bed is produced by compressing loose powder into a wafer with a particle volume fraction of $\phi _\mathrm{p} = 0.48$ . The wafer is positioned inside the shock tube, uniformly filling the entire cross-section. This results in a clean experiment where no flow obstructing support structures are present. Through high-speed shadowgraph imaging and pressure measurements along the length of the channel, detailed information about the particle shock interaction was obtained. Due to the limited strength of the incident shock wave, no transmitted shock wave is produced. The initial solid-like response of the particle wafer acceleration forms a series of compression waves that eventually coalesce to form a shock wave. Breakup is initiated along the periphery of the wafer as the result of shear that forms due to the fixed boundary condition. Particle breakup is initiated by local failure sites that result in the formation of particle jets that extend ahead of the accelerating, largely intact, wafer core. In a circular tube, the failure sites are uniformly distributed along the wafer circumference. In a square channel, the failure sites, and the subsequent particle jets, initially form at the corners due to the enhanced shear. The wafer breakup subsequently spreads to the edges forming a highly non-uniform particle cloud.     

空化可压缩流动空穴溃灭激波特性研究

为深入研究空化可压缩流动中空泡/空泡团溃灭过程中激波产生、传播及其与空穴相互作用规律,本文采用数值模拟方法对空化可压缩流动空穴溃灭激波特性展开了研究.数值计算基于OpenFOAM开源程序,综合考虑蒸汽相和液相的压缩性,通过在原无相变两相可压缩求解器的控制方程中耦合模拟空化汽液相间质量交换的源项,实现了对空化流动的非定常可压缩计算.利用上述考虑汽/液相可压缩性的空化流动求解器,对周期性云状空化流动进行了数值模拟,并重点研究了空穴溃灭激波特性.结果表明:上述数值计算方法可以准确捕捉到空穴非定常演化过程及大尺度脱落空泡云团溃灭激波现象,大尺度脱落空泡云团溃灭过程分为3个阶段:(1) U型空泡团形成; (2) U型空泡团头部溃灭; (3) U型空泡团腿部溃灭.在U 型空泡团腿部溃灭瞬间,观察到激波产生,并向上游和下游传播,向上游传播的激波与空穴相互作用,导致水翼吸力面新生的附着型片状空穴回缩,直至完全溃灭.并且空穴溃灭激波存在回弹现象, 抑制了下一周期的空化发展.      

Lifting of Disperse Particles from a Cavity Behind the Front of an Unsteady Shock Wave with a Triangular Velocity Profile

The gas flow in plane shock waves slipping along an impermeable surface with a rectangular cavity where solid disperse particles are suspended is considered numerically. The motion of the gas and particles (gas suspension) is modeled by equations of mechanics of multiphase media. Some laws of the behavior of the dusty cloud in the cavity are established for the case of wave interaction with the cavity.     

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     

Two-phase reactive particle flow through normal shock waves

An analysis is presented for the steady one-dimensional flow behind a normal shock wave of a compressible gas containing small spherical particles of solid propellant. The solids mass fraction is assumed large enough to require that the void volume fraction be retained as a variable in the governing conservation equations. The particles are ignited by the shocked air and by viscous interaction. Propellant gases are then generated which depend on the instantaneous size of the particles and on the linear burning rate. The latter is assumed dependent upon the local pressure and the particle temperature. These calculations are of interest because of the potential hazards of such particle flows, in that extreme pressures are predicted within the relaxation zone, pressures even greater than those calculated for the final equilibrium conditions. The results stress the importance of the Mach number of the normal (strong shock) and the energy content of the propellant (J/kg).     

Aerodynamic characteristics of solid particles�� acceleration by shock waves

In this study, the interaction of a planar shock wave with a group of particles has been investigated using high-speed photography and dynamic pressure measurements. Experiments were carried out in a horizontal circular shock tube. The influence of the particle loading ratio, particle diameter, driving gas and shock wave Mach number on the acceleration was studied. It was found that the higher the particle loading ratio, the greater was the particle velocity. This is due to the higher driving pressure. Helium and nitrogen gases play quite different roles in acceleration. Pressure multiplication during shock wave interaction with particles also appears. Based on the experimental results, the discussion regarding partial quantitative velocities and accelerations of particle groups, as well as the attenuation factors when shock waves pass through the particles, is given.