爆炸激波管出口流场特征的纹影诊断与分析

冲击波是爆炸毁伤的主要载荷形式之一,炸药驱动激波管是较真实复现高超压冲击波场景的可能方式,当前亟需关注冲击波与产物分离状态、波阵面形态等实验参数测试问题,仅依靠传统电测原理的单一点源压力测量无法满足上述流场表征需要。基于反射式纹影原理并利用激光光源和系列光学元件,搭建了一套激波管出口流场诊断系统,将流动现象的可视化观测结果与传统压力测量相结合,完善流场特征诊断与分析方法。研究表明,该纹影系统能够清晰获得激波管出口的冲击波和产物运动流场图像,通过与压力测试与激波管点火时序的同步控制,可有效揭示压电式冲击波压力传感器数据振荡、压力突变、漂移等特征,以及爆炸后管道中应力波引起的管口及空气振动等现象。基于图像分析可分析获得炸药爆炸激波管出口冲击波运动速度和压力的空间衰减特性,该结果为更好理解炸药驱动激波管冲击波压力的形成和演化规律研究提供了诊断途径和分析基础。     

激光聚变冲击波被动式测速光学系统设计

针对激光聚变装置冲击波速度被动测量的需求,设计了一种测速光学系统。采用高紫外透过率的氟化玻璃,实现了透射式300～800nm复消色差设计。系统光路具有前后两组镜头,中间为平行光,镜头间距可变,光路适应能力强。系统前端两侧的双目机器视觉能够完成自动寻的。平行光路中设置5个激光器,轴上的1个前向照明靶点用来观察条纹相机狭缝处的目标像质,轴外的4个与光轴平行后向传输用来标识系统光轴的位置,激光器部件可电动切入/切出。系统前组镜头F/#数为4,宽谱工作物方分辨率优于10μm,532nm单波长工作物方分辨优于5μm。该光学系统光路排布灵活,可单独被动测速,也可与主动测速系统VISAR耦合构成主被一体复合测速系统,满足激光聚变装置冲击波测速的需求。     

激光等离子体X射线特征谱轮廓诊断

开展了利用X射线特征谱轮廓诊断激光等离子体状态参数的研究。在"神光II"激光装置上,将0.35μm频谱激光束聚焦于真空室内固体氯(Cl)元素靶上产生激光氯等离子体,利用高分辨X射线椭圆弯晶谱仪获取高能谱分辨激光氯等离子体辐射的X射线精细结构能谱。用类氢(1s-3p)和类氦(1s2-1s3p)氯离子能级跃迁光谱线的光强度比率计算了激光等离子体的电子温度;然后在假定光性为薄的情况下,利用X射线谱线Lyman-线形轮廓的Stark效应所产生的谱线展宽测量了等离子体的电子密度。实验获得的激光等离子体日冕区内体平均电子温度约为450eV,电子密度约为7.5×1022 cm-3。文中还简单分析了能谱线的半高全宽度(FWHM)值以及诊断过程引入的诊断误差,初步预估诊断误差可控制在25%以内。该项工作为X射线特征谱轮廓法进一步应用于激光聚变靶丸压缩度精度测量等工作提供了参考。     

激光聚变冲击波速度测量光学系统设计

针对激光聚变冲击波速度测量的需求,设计了一种集被动式扫描高温计和主动式冲击波速度测量于一体的复合冲击波速度测量系统。通过采用多种耐辐射光学玻璃材料,实现了共用光路的400~700 nm耐辐射消色差设计;通过采用自动控制干涉仪简化了系统操作;主动测速系统通过切换不同焦距的中继成像镜头,实现了不同放大倍率的切换。系统的物方视场为φ2.0 mm,主动式测速系统的放大倍率为10×,20×,30×,静态实验干涉条纹平直,调制度达到0.69以上,物方分辨率达到4.72μm。该系统在激光聚变装置上能够实现冲击波速度的动态测量。     

激光诱导空化微孔冲裁试验研究

针对微尺度下金属箔模具冲孔存在模具挤压磨损、对中困难,激光打孔存在烧蚀、吸收层无法补偿等问题,提出通过激光诱导空泡对金属箔进行加载来实现冲裁小孔的方法。研究了不同激光焦点位置(H=0~4 mm)、激光能量(E=10.3~50.8 mJ)和铜箔厚度(T=20~70μm)对铜箔冲孔的影响,发现激光焦点位置影响明显,当铜箔变形平均深度达到147.0μm后,铜箔发生剪切断裂,可实现冲裁,并且制备的小孔边缘正表面无烧蚀、毛边、裂纹和卷边等缺陷。同时,利用高速摄影仪对激光诱导空化微孔冲裁过程进行研究,结果表明激光诱导空化微孔冲裁过程是激光等离子体冲击波、空泡溃灭冲击波和微射流共同加载的过程。     

齿轮倒角轮廓协同高精度测量方法的研究

为实现对制造业中复杂工件(如汽车变速箱中的倒角齿轮)表面轮廓的快速、精密测量,研制了协同视觉表面轮廓测量系统。对该系统中采用的图像处理、测量路径的规划进行了研究。首先使用面阵图像传感器拍摄齿轮图像,对图像进行边缘处理,利用齿轮的边缘点拟合齿轮的中心,在结合标定算法定位齿轮倒角的待测局部区域。然后,根据测量要求规划测量路径,驱动XY电动平台携带高精密的点视觉激光位移传感器沿测量路径完成对带测量区域的测量。最后,使用计算机对激光位移传感器所测得数据进行处理,输出测量报告。该系统经工厂实际测量验证,对齿轮倒角表面轮廓的高度方向(Z方向)测量精度为1μm,对X和Y方向的测量精度达到5μm以上。结合图像传感器测速快,激光传感器精度高的优点,提出一种利用图像传感器实现高速定位,激光传感器实现精密测量的协同高精度视觉测量方法,并将其用于了齿轮倒角轮廓的测量。     

微塑性成形中的激光冲击脱模研究

针对微成形技术中存在的脱模问题,提出利用激光冲击波在模具与工件界面上产生界面力进行脱模的新工艺。根据冲击波在介质中传播的特点,分别从冲击波垂直入射、冲击波脱模压力的计算、冲击波斜入射的角度讨论激光冲击波脱模的机理;然后在LS-DYNA软件中进行数值模拟,分析工件从模具上脱落的过程,并进一步讨论在一定冲击波压力下工件的脱模性能;最后按照数值模拟条件进行脱模实验,证实激光冲击波脱模的可能性。     

冲击波测量用压力传感器准静态校准方法

阐明了冲击波测量的意义,介绍了目前用于冲击波测量的方法,分析了这类方法存在的问题,为提高冲击波的测量精度,针对存在的问题,提出了一种适用且新颖的准静态冲击波测量用压力传感系统的校准方法-利用落锤液压动标装置对冲击波测量用压力传感系统实施准静态的绝对校准.     

激光聚变靶丸内表面轮廓测量系统的研制

针对激光聚变靶丸内表面轮廓高精度无损测量的迫切需求,研制了一套激光聚变靶丸内表面轮廓测量系统。该系统通过最小二乘算法(LSC)计算出靶丸回转偏心量,并利用偏心调整台对靶丸偏心进行自动快速调整;然后,系统软件控制气浮回转轴承驱动靶丸旋转,利用激光差动共焦传感器(LDCS)轴向响应曲线过零点及光线追迹算法精确计算出靶丸内表面轮廓上每个采样点的几何位置;最后,对靶丸内轮廓测量数据进行LSC评定得到其圆度信息。实验证明,靶丸回转偏心的自动调整时间可达22s,当采样点分别为1 024,2 048及4 096时,靶丸内轮廓测量时间分别可达10,20及40s,且圆度测量标准差可达19nm(1 024点)。该系统实现了靶丸回转偏心的自动快速调整及其内轮廓的高精度、无损、快速、自动测量。     

激光加工技术探讨

以讲解激光加工技术组成为主,分类介绍了利用激光进行切割、焊接、和合金化以及利用激光冲击波等加工技术及其特点,并对激光加工技术的发展趋势进行了展望。     

超高压水射流中空化现象对轮胎破碎作用研究

为了探讨超高压水射流破碎轮胎过程中,冲击波和微射流的作用机理,基于FLUENT软件环境,采用VOF模型求解Navier-Stokes方程,数值模拟了近壁面的空泡溃灭过程,结果表明,射流冲击物面时,空泡溃灭产生的压力脉冲远大于微射流产生的冲击压力。结合超高压水射流破碎轮胎试验,通过对胎面胶的切槽断面形貌进行观察,研究了微射流和冲击波对橡胶材料的破坏作用,认为橡胶材料在受到空化作用破坏时,表现出明显的冲击脆化现象,微射流在材料壁面冲击出边缘齐整的针孔状形貌,冲击波引发材料产生拉伸破坏。     

谐振管内非线性驻波的间断Galerkin方法*

基于伪一维瞬态可压缩Navier-Stokes方程和理想气体状态方程,并结合保持强稳定性的三阶Runge-Kutta格式和斜率限制器技术,构建一种整体轴向谐振激励下求解变截面谐振管内非线性驻波的间断Galerkin方法。分别对直圆柱形、指数形以及圆锥形谐振管内的非线性驻波进行数值仿真计算,通过与现有数值仿真结果对比,验证了本方法的正确性,并重现了已有试验中非线性驻波压力波形中的第二峰值。在直圆柱形和指数形谐振管内研究间断Galerkin方法的两种网格加密方式对于不同形状下谐振管内非线性驻波仿真计算的数值精度、消除数值振荡和准确捕捉激波的不同作用,以及不同CFL数对于数值精度的影响。在指数形谐振管内,通过与有限体积法不同网格数目下的数值仿真结果和计算时间对比,验证了本方法具有耗时短、效率高以及计算精度高的优点。在圆锥形谐振管内,研究不同流速下谐振管内压力和速度波形的变化,并发现随着流速的增加,谐振管小端处的压力幅值增加,大端处速度幅值也随之增加且速度波形中会产生激波。通过间断Galerkin方法分析研究几种谐振管内非线性驻波的各种物理属性,为谐振管形状优化提供了重要参考,也为实现谐振管内非线性驻波的工程应用奠定了良好的基础。     

Time-dependent characteristics of the nonequilibrium condensation in subsonic flows

High-speed moist air or steam flow has long been of important subject in engineering and industrial applications. Of many complicated gas dynamics problems involved in moist air flows, the most challenging task is to understand the nonequilibrium condensation phenomenon when the moist air rapidly expands through a flow device. Many theoretical and experimental studies using supersonic wind tunnels have devoted to the understanding of the nonequilibrium condensation flow physics so far. However, the nonequilibrium condensation can be also generated in the subsonic flows induced by the unsteady expansion waves in shock tube. The major flow physics of the nonequilibrium condensation in this application may be different from those obtained in the supersonic wind tunnels. In the current study, the nonequilibrium condensation phenomenon caused by the unsteady expansion waves in a shock tube is analyzed by using the two-dimensional, unsteady, Navier-Stokes equations, which are fully coupled with a droplet growth equation. The third-order TVD MUSCL scheme is applied to solve the governing equation systems. The computational results are compared with the previous experimental data. The time-dependent behavior of nonequilibrium condensation of moist air in shock tube is investigated in details. The results show that the major characteristics of the nonequilibrium condensation phenomenon in shock tube are very different from those in the supersonic wind tunnels.     

A numerical study of shock wave/boundary layer interaction in a supersonic compressor cascade

A numerical analysis of shock wave/boundary layer interaction in transonic/supersonic axial flow compressor cascade has been performed by using a characteristic upwind Navier-Stokes method with various turbulence models. Two equation turbulence models were applied to transonic/supersonic flows over a NACA 0012 airfoil. The results are superion to those from an algebraic turbulence model. High order TVD schemes predicted shock wave/boundary layer interactions reasonably well. However, the prediction of SWBLI depends more on turbulence models than high order schemes. In a supersonic axial flow cascade at M=1.59 and exit/inlet static pressure ratio of 2.21, k-μ and Shear Stress Transport (SST) models were numerically stables. However, the k-μ model predicted thicker shock waves in the flow passage. Losses due to shock/shock and shock/boundary layer interactions in transonic/supersonic compressor flowfields can be higher losses than viscous losses due to flow separation and viscous dissipation.     

超高速弹丸斜侵彻水现象的试验研究

利用新型可调发射角立式二级轻气炮发射高超声速弹丸,基于光反射原理和光电二极管测量弹丸出口速度,采用脉冲火花光源和连续激光光源拍摄高速弹丸斜侵彻水流场的纹影和阴影图像。结果表明,对于锥柱（圆柱和圆锥组合体）弹丸,弹丸入水前,其头部产生斜激波,尾部羽流膨胀并产生斜激波系;弹丸入水时,其头部斜激波对气水界面几乎无影响;弹丸入水后,其头部和羽流斜激波在气水界面产生复杂反射,弹丸斜侵彻产生的水喷射和飞散非对称地分布在其轨迹两侧。圆柱弹丸受波阻较大且减速较快,发射管羽流越过弹丸并和气水界面率先作用,高温羽流也出现和弹丸侵彻类似的非对称水喷射和飞散。2种情况下,弹丸和水侵彻后均产生在水中传播的半球形激波,弹丸尾流出现空化区,较大的水阻力导致弹丸减速很快。弹丸羽流和气水界面产生的水激波较弱。     

Simulating sympathetic detonation using the hydrodynamic models and constitutive equations

A Sympathetic detonation (SD) is a detonation of an explosive charge by a nearby explosion. Most of times it is unintended while the impact of blast fragments or strong shock waves from the initiating donor explosive is the cause of SD. We investigate the SD of a cylindrical explosive charge (64 % RDX, 20 % Al, 16 % HTPB) contained in a steel casing. The constitutive relations for high explosive are obtained from a thermo-chemical code that provides the size effect data without the rate stick data typically used for building the rate law and equation of state. A full size SD test of eight pallet-packaged artillery shells is performed that provides the pressure data while the hydrodynamic model with proper constitutive relations for reactive materials and the fragmentation model for steel casing is conducted to replicate the experimental findings. The work presents a novel effort to accurately model and reproduce the sympathetic detonation event with a reduced experimental effort.     

一个用流函数方程求解叶轮机械S1流面跨音速问题的方法

本文在非正交曲线坐标上用流函数方程求解了跨音速问题。将离散形式的能量方程与离散形式的动量方程联立迭代求解,从而克服了由于采用流函数而必然带来的密度双值问题。本文提出了一种新的熵耗散方法,无需采用J.Von Neumann和R.D.Richtmyer提出的人工粘性耗散,只要计算出跨过激波的熵增,就可以得到一个稳定的,仅占据一个网格宽度的激波。无论流场中有多少道激波,都无需专门得理。从理论上讲,只要网格分得足够细,就可以得到任意窗的激波。值得指出的是本文提出的方法对一般的跨音速问题都是适用的,而不仅仅限于叶轮机械。     

Calculation of the Flow in High-Speed Gas Bearings Including Inertia Effects Using the CE/SE Method

In the classical Reynolds equation, inertia effects are neglected. Gas bearings working at very high speeds may encounter flow discontinuities (shock waves), which require the inclusion of inertia terms within the momentum equations. In order to solve the resulting system of equations, a numerical method capable of capturing flow discontinuities is necessary, and the space-time conservation element/solution element (CE/SE) is such a method. In addition, it does not incorporate any other assumptions or special numerical treatment. Results obtained using this method are compared with experimental data and theoretical results, as well as with results obtained by neglecting inertia effects.     

Morphological transformation of shock waves behind a flat plate

The interaction of a travelling shock with the shear layer of a flat plate is studied computationally. The Euler and Navier-Stokes equations are solved numerically on quadrilateral unstructured adaptive grids. The flat plate is installed horizontally on the central axis of a shock tube. The shear layer is first created by two shock waves at different speeds splitted by a flat plate. A series of small vortices is developed as a consequence in the shear layer. The shock wave reflected at the end wall impinges the shear layer. The complicated shock dynamics in the evolution to the pseudo-steady state is represented with the morphological transformation of a planar shock into an oblique shock.