微喷颗粒与气体混合过程的数值模拟研究

冲击波作用下金属与气体界面将发生微喷混合现象,即金属表面产生的微喷射物质在气体中的输运过程.提出采用散体颗粒分布代替微喷初始状态,基于气体-颗粒两相流模型对微喷混合现象进行了模拟研究.数值模拟给出了微喷混合的动力学演化过程,分析了初始气体压力和颗粒尺寸因素对混合层的影响规律;在数值模拟中发现了微喷颗粒的气动破碎现象,这可导致颗粒尺度明显减小,成为影响微喷混合演化性质的重要物理因素.本文模拟结果与相关实验结果取得一致,初步表明,气粒两相流模型是模拟微喷混合过程的一种有效方法.     

冲击波作用下微米尺度金属颗粒群的动力学行为

基于平面化爆驱动飞片高压加载技术和激光测速技术,研究了冲击波加载不同粒径锡颗粒群的微喷射行为以及在空气中的减速规律.实验结果表明,锡颗粒的最快喷射速度随粒径增大而显著增大.通过对微喷射形成过程的三维光滑粒子流体动力学方法数值模拟发现,大粒径锡颗粒之间存在较大的空隙结构,冲击波与空隙结构的相互作用诱导产生高速汇聚射流,空隙结构越大对应的喷射速度也越高.此外,通过研究不同粒径颗粒在复杂流场中的减速规律,进一步深化了对微喷射破碎后的颗粒尺度状态以及混合输运特性的认识.研究结果对于预测和分析冲击波加载微米颗粒群的微喷混合特性具有一定价值.     

二维拉格朗日坐标系下气粒混合双向耦合对激波流场影响的计算

喷射颗粒与气体混合是内爆压缩领域的热点和难点. 针对喷射混合中的气粒双向耦合问题, 开展了理论建模、离散算法以及颗粒反馈对激波流场的影响研究. 建立了拉格朗日计算框架下的数学模型; 给出了耦合源项的离散算法; 开展了平面及汇聚构型条件下, 气粒双向耦合的数值模拟研究; 发现了颗粒反馈导致气体激波提速现象以及气区流场物理量分布形态的改变, 初步获得了量化分析结果. 本文建立的数学模型、计算方法和获得的新的物理认识, 为深入理解喷射混合现象、解决相关工程应用问题提供了重要理论支撑.     

强激光加载下锡材料微喷颗粒与气体混合回收实验研究及颗粒度分析

冲击波在金属材料自由面卸载时,材料表面会形成微颗粒向外喷射,这是材料表面一种特殊的破坏形态.在内爆压缩和高压工程领域的相关物理过程中,微喷射颗粒是引起界面混合现象的重要来源,会直接影响后期的混合状态和压缩过程.而微颗粒的尺寸、形态、运动速度等是开展微喷混合过程理论和数值模拟研究的重要参数.由于实验中动态诊断的难度较大,目前已获取的微喷颗粒尺寸及分布数据十分有限.基于神光Ⅲ原型激光装置,本文设计并开展了强激光驱动冲击加载,锡材料微喷颗粒经过气体区混合后,低密度泡沫材料对微颗粒进行回收分析的实验研究.通过对微喷颗粒回收样品的X光电子计算机断层扫描分析和图像重建,获得了两个典型加载压强条件下与气体混合后微喷颗粒的三维图像,通过与真空实验条件下回收微喷颗粒图像的对比分析,对混合后的微喷颗粒分布形态有了初步的认识;测量统计了回收颗粒尺寸与数目,并通过分析,给出了微喷颗粒尺寸的双指数分布规律.     

共振散射对微球颗粒光子喷射流的影响

研究了光子喷射流特征参数与颗粒物性参数之间的关系,包括不同偏振模式共振和非共振散射条件下光子喷射流的物理机理。通过理论计算,数值分析了非共振情况下光子喷射流特征参数与折射率和颗粒粒径的关系;研究了共振散射对光子喷射流特征的影响,分析了共振散射分波在其中的作用;比较了线偏振和圆偏振入射光照射下光子喷射流的差异。研究表明:共振散射对光子喷射流的影响主要体现在焦点宽度减小、焦点向颗粒表面内移、光子喷射流长度缩短、焦点处强度增大以及场分布更加复杂;TE和TM共振下电场径向和横向分量的相对强度存在差异;入射光偏振态仅影响电场的横向分布。通过控制入射光和颗粒参数,调制光子喷射流的特征参数及场分布特征,可为光子喷射流在不同场合的应用提供理论依据。     

强激光间接驱动材料动态破碎过程的实验技术研究

强激光驱动加载已成为冲击波作用下材料动态破碎过程研究的一种有效手段.采用间接驱动方式,设计合适的腔型进行物理实验研究,可实现更大且更均匀的冲击加载一维区.采用数值模拟和物理实验方法,研究强激光间接驱动材料动态破碎过程的实验技术.首先,利用IRAD程序设计适用于开展动态破碎过程研究的半柱腔,其直径为2 mm、腔长为2 mm;进而通过物理实验获得此腔型下多个激光能量点、脉宽2 ns和3 ns条件下辐射峰值温度和波形;最后,利用流体模拟方法给出多种辐射波形下的冲击加载波形.利用高能X射线成像和光子多普勒干涉仪诊断给出间接驱动加载下层裂过程的物理图像和速度历史.经分析发现,间接驱动的加载一维区达到2 mm,平面性优于5%,能有效地开展相关物理实验研究.研究结果为新型柱腔设计、冲击加载技术及动态破碎过程研究提供了重要的研究基础.     

双石英玻璃珠的低速冲击破碎行为

应用分离式霍普金森压杆(SHPB)加载装置,对直径为8.30、11.68、15.42、17.50 mm的石英玻璃珠开展了冲击速度为5.6~11.5 m/s的双玻璃珠系动态破碎实验。利用高速摄影技术记录双玻璃珠在动态冲击下的破碎过程,结合透射载荷-位移曲线以及破碎产物的粒度分析结果,探讨了石英玻璃双颗粒在冲击下的破坏机制。结果表明:由于双颗粒系中载荷的不均匀特性,两个玻璃珠的破碎具有时序特征,随冲击速度的增加而改变;玻璃珠的冲击破碎源于接触部位局部的Hertz裂纹扩张和裂纹系的扩散,而不是通常认为的贯穿性的斜裂纹体系;瞬态红外测温揭示了玻璃珠冲击破碎的两种主要机制和临界破碎扩散阻力的存在。研究结果对认识脆性颗粒介质的动态破坏机制具有良好的参考意义。     

气体混合流动的DSMC方法模拟

气体混合流动在MEMS的应用中常常遇到.本文采用直接模拟Monte Carlo方法研究了氮气和氧气在微尺度中的流动混合问题.数值模拟中设定两种气体分别以不同的速度,相同的数密度进入微槽道.当经过分割平板之后,两种气体发生混合.在对结果的分析中发现,进入速度对两种气体完全混合后的混合距离,以及完全混合后的单组份气体占混合气体的比例都会产生重要的影响.     

微尺度稀薄效应下颗粒沉降的格子Boltzmann方法模拟

基于多松弛格子Boltzmann模型,对竖直细长微通道内颗粒自由沉降过程进行模拟,分析气体稀薄效应、初始位置以及颗粒间相互作用对微颗粒沉降特性的影响.研究表明：随Knudsen数增大,微通道内气体稀薄效应增强,颗粒表面气体滑移速度增大,气相流体有效粘度减小,颗粒相同运动状态下受到气体阻力相应减小,颗粒沉降平衡速度明显增大;不同初始位置颗粒沉降过程存在明显差异,初始位置偏离中心线颗粒将发生水平方向位移且呈振荡趋势,最终稳定于中心线平衡位置;在微尺度双颗粒沉降DKT现象过程中,气体稀薄效应影响颗粒运动特性,后颗粒跟随过程明显增长.     

颗粒物质在冲击作用下的堆积分布

沙堆在冲击作用下的行为和静态沙堆的行为有着很大的不同.通过管道产生“高斯冲击”(速度水平分量成高斯分布)来研究沙堆堆积时的分布情况，发现沙堆自身的稳定性和外界冲击是影响沙堆形状的两大重要因素.给出了沙堆在冲击作用下高度随时间的演化方程.通过该方程，成功地得到了沙堆中心点的高度与外界参量之间的关系，并且提出了一种节能高效的颗粒混合方法. 关键词： 颗粒物质 堆积 高斯分布 冲击     

Reconstruction and interpretation of photon Doppler velocimetry spectrum for ejecta particles from shock-loaded sample in vacuum

The photon Doppler velocimetry(PDV) spectrum is investigated in an attempt to reveal the particle parameters of ejecta from shock-loaded samples in a vacuum. A GPU-accelerated Monte–Carlo algorithm, which considers the multiplescattering effects of light, is applied to reconstruct the light field of the ejecta and simulate the corresponding PDV spectrum.The influence of the velocity profile, total area mass, and particle size of the ejecta on the simulated spectra is discussed qualitatively. To facilitate a quantitative discussion, a novel theoretical optical model is proposed in which the singlescattering assumption is applied. With this model, the relationships between the particle parameters of ejecta and the peak information of the PDV spectrum are derived, enabling direct extraction of the particle parameters from the PDV spectrum.The values of the ejecta parameters estimated from the experimental spectrum are in good agreement with those measured by a piezoelectric probe.     

Photon Doppler Velocimetry and Simulation of Ejection of Particles from the Surface of Shock-Loaded Samples

The results of photon Doppler velocimetry of ejecta from shock-loaded metal samples are reported. The experiments have been performed with tin and lead samples of a given thickness and a given surface roughness. The direct numerical simulation of the process of mass ejection from the surface of shock-loaded samples is performed for conditions close to experimental by the smoothed particle hydrodynamics method. The areal density and initial velocity distribution of the volume density of ejecta are determined. Using these results, we calculate the time dependence of the profile of the volume density at the expansion of the formed dust cloud to air. Applying an approach based on the transport equation for the correlation function of the scattered field, the main parameters of the velocity distribution of ejecta, areal density of ejecta, etc. are reconstructed from spectral photon Doppler velocimetry data. The experimentally observed temporal dynamics of spectra, which is caused by the drag of dust in air, is described at an appropriately chosen size dispersion of dust particles. The masses of ejecta reconstructed from experimental data are in agreement with the smoothed particle hydrodynamics results.     

熔化状态下金属样品表面的微喷射问题

熔化状态下金属样品表面微喷物质的时空演化规律是目前国内外研究关注的热点问题,不过,由于压电石英计等传统诊断技术能力的限制,导致目前对该问题的认识仍存在明显不足.本文采用作者前期发展的大量程Asay-F窗技术,结合传统压电石英计,通过将其布置在距受载Sn样品自由面不同高度位置处的方法,系统研究了熔化Sn样品表面微喷物质的运动演化规律,给出了特定时刻微喷物质的密度-空间分布图像.本文研究结果从实验上确认了微喷物质时空演化过程中的"自相似膨胀"规律,成功避免了传统压电石英计由于测量量程偏低导致其获取物理认识不够全面的问题,为认识动载下金属材料的微喷运动演化规律提供了重要实验支撑.     

高速流动PIV示踪粒子跟随性分析

通过理论推导提出了一种评价高速流动PIV示踪粒子随流能力的松弛特性分析模型,在法向Mach数大于1.4时具有良好的适用性.将新模型应用于试验测量,发展了高速流动PIV系统和示踪粒子布撒技术,验证了高速流动PIV的定量化测量能力.针对空间发展的二维超声速气固两相混合层,数值模拟了不同Stokes数和对流Mach数（M_c）下的粒子跟随性以及弥散和迁徙运动,结果表明:相同对流Mach数,粒径越小的示踪粒子跟随性越好,Stokes数在[1, 10]范围内的粒子有最大扩散距离.示踪粒子的直径大小决定其在超声速混合层大涡拟序结构中的分布特征,且粒径越小,气体与粒子的掺混越剧烈.相同粒径的粒子,对流Mach数越大跟随性越差.      

Effect of the incident shock wave interacting with transversal jet flow on the mixing and combustion

The interaction between an incident shock wave and a transverse jet flow for mixing and combustion in a supersonic airstream was investigated experimentally and numerically. NO planar laser induced fluorescence (NO-PLIF) and particle imaging velocimetry (PIV) for non-reactive flows and three-dimensional reactive/non-reactive numerical simulations were conducted to examine the effect of the incident shock wave on the three-dimensional flow structure and mixing mechanism between the airstream and the injected gas downstream of the injection slot. Results of NO-PLIF measurement and numerical simulation showed that, in the case without the incident shock wave, injected gas is seldom seen in the recirculation zone just downstream of the injection slot, while the injected gas with higher concentration is almost uniformly distributed in the recirculation zone when the incident shock wave is introduced downstream of the injection slot. Moreover, it was shown by the numerical simulations that the profiles of the local equivalence ratio is in the combustible range due to the enhanced entrainment of the airstream when the incident shock wave is introduced downstream of the injection slot. A large-scale recirculation in the direction parallel to the wall is generated by the three-dimensional flow effects, which enhances the mixing and extends the residence time in the recirculation zone in the case with incident shock wave downstream of the injection slot, the recirculation flow being confirmed successfully by PIV measurements as well. The results of three-dimensional reactive numerical simulations were in good agreement with the experimental flame-holding characteristics at a lower total temperature, which showed that flame-holding can be attained only when the incident shock wave was introduced downstream of the injection slot, confirming that the formation of three-dimensional and large-scale recirculation flow downstream of the injection slot enlarges the recirculation zone and enhances the mixing to produce the conditions for robust flame-holding.     

Bi在固液混合相区的冲击参数测量及声速软化特性

冲击相变与熔化作为材料特性的一项重要研究内容,对于多相物态方程构建具有重要意义.本文利用追赶稀疏原理和阻滞法,基于火炮加载技术获得了17.3—28.3 GPa范围内纯铋(Bi)的高精度声速数据和Hugoniot参数,分析了声速软化规律,得到固-液混合相区Bi材料声速随压力的近似线性递减关系C=3.682-0.015p,并进一步确定Bi的冲击熔化压力区间为18—27.4 GPa.同时,Bi/Li F界面速度剖面的预期平台段在固液混合相区表现出渐进爬升的异常特征,分析认为,该现象与Bi材料的非均匀熔化动力学行为及冲击熔化完成时间尺度较长有关.     

斜波压缩下锡的相变动力学特性

利用磁驱动加载装置(CQ-4)和高精度速度测试装置(DPV),开展了斜波加载下锡的动态压缩实验。实验结果表明:锡在加载阶段经历了弹塑性转变和相变等物理过程,相变压力约为7.5 GPa。β–γ相变对应的特征速度随着锡厚度的增加,从676.3 m/s减小到636.8 m/s,对应的压力从7.62 GPa降低到7.11 GPa。结合Hayes多相状态方程和非平衡相变动力学模型,对锡的斜波压缩实验过程进行了模拟,数值计算结果可以较好地描述锡在加载阶段的弹塑性转变和相变等物理过程。讨论了体模量在不同热力学过程中的物理形式,计算结果显示,斜波压缩过程需考虑压力对体模量的修正。分析了相变弛豫时间、体模量等典型物理参数对速度波形的影响,结果表明,相变弛豫时间和各相初始自由能主要影响混合区部分速度波形,γ相的体模量参数只影响相变后的速度波形,β相的体模量参数会影响整体速度波形。     

Numerical studies on velocity, temperature history and heat transfer to the particles injected into the argon plasma

A new approach to study the particle velocity in a thermal plasma in relation to input parameters (power, gas flow rate, injection velocity of the particle and particle size) and nozzle dimensions (nozzle length and diameter) has been made. Injected particle's temperature and thermal history were calculated for particles of three different materials (alumina, tungsten and graphite) in argon plasma. Allowable powder feed rate was calculated for the particles. Heat transfer per particle injected in to the plasma is reported. Liquid fraction of the particle after it reached the melting point is also reported. Particle velocity is found to increase with increase in power, gas flow rate and injection velocity and decrease with increase in particle size, nozzle length and nozzle diameter. Thermal histories of the particles in relation to the plasma temperature and particle diameter are presented. Particle's residence time is found to increase with increase in diameter of the particle. Allowable powder feed rate for complete melting of the particle is higher at higher percentage utilisation of the plasma power. Powder feed rate is seen to decrease with increase in particle size and it is higher for tungsten and lower for graphite particle. Heat transfer rate from plasma to particle is seen to decrease with increase in time and the same is higher for plasmas of higher temperature and smaller sized particle. Received 4 May 2000 and Received in final form 15 March 2001