水洞流场PIV显示与分析系统离轴测试校正

粒子图像测速技术(PIV)通过测量被测流场截面上每一位置点的速度,获得整个被测流场的信息.在PIV一般应用中所使用的照明激光片光与成像CCD装置的拍摄方向是垂直的,在某些应用场合受测试条件的限制,需要采用离轴方式进行测量,此时CCD成像方向与照明的激光片光不垂直,而是有一定夹角.离轴测试方式将对PIV系统的光学成像系统、示踪粒子选择和粒子图像处理带来影响.实验采用Scheimpflug离轴聚焦的方法对表面镀银高反射率的示踪粒子进行成像,通过调整成像透镜与CCD像面的夹角可获得清晰的粒子成像,并利用网格校正板和软件计算处理等方法有效校正了由于离轴测试带来的影响.     

用于彩色光照粒子图像测速的粒子场模拟成像

分析了基于彩色光照的粒子图像测速算法中示踪粒子的成像原理,并根据实际流场中的应用环境以及彩色粒子图像测速算法的实验条件,采用一套由白色光源和波长线性变化的滤波片组成的照明系统,为粒子场提供不同深度、相同光强的彩色体积光照明.根据针孔相机模型和其对应的点扩散函数,建立示踪粒子的三维成像模型,得到在彩色体积光照射下流场中的...     

应用于微细流场的全息荧光粒子图像三维测速系统

利用亚微米荧光示踪粒子的离焦微细观测时的衍射图样,可以分析确定荧光粒子垂直于图像平面的轴向的位置, 实现对示踪粒子的三维定位．再结合应用于二维流畅测速领域的PIV技术,可利用全息荧光粒子图像测速技术实现流体速度分布的三维测量。     

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.      

微纳级示踪粒子图像灰度与粒径量化关系研究

基于传统粒子追踪测速(PTV)技术的粒径分析方法只能通过几何成像检测粒径,无法对衍射成像尺寸远远大于几何成像尺寸的粒子图像进行分析。根据衍射成像原理,通过对激光-粒子散射光-CCD信号-图像灰度值物理流程的定量分析,提出确定微纳米级示踪粒子图像灰度值与粒径之间量化关系的模型,弥补了PTV技术在粒径检测方面的不足。基于PTV实验系统,应用数字相机和Micro Vec V3软件完成SiO_2粒子图像的拍摄,运用所提模型对拍摄的粒子图像进行粒径分析。实验结果表明,所提方法具有较高的准确性。     

单相机离焦法测量粒子三维运动轨迹

本文提出一种测量空间粒子三维运动轨迹的新方法。该方法是当利用双孔透镜成像时,单点粒子在离焦光学成像系统中会形成包含粒子空间信息的两点像,根据粒子像在像平面上的位置和间距可以获取空间粒子的三维空间位置。本文用单点发光体模拟单点粒子,用ＣＣＤ摄像机连续摄取粒子的瞬时空间运动图像,用计算机对获得的图像进行处理,可以得到粒子三维运动轨迹。这种方法可以应用于三维流场的流动显示研究     

PIV技术在气体界面不稳定性实验研究中的应用

采用粒子图像测速(Particle Image Velocimetry,PIV)技术,以乙二醇烟雾作为示踪粒子,实验测量了平面激波作用下SF6气柱-空气界面Richtmyer-Meshkov不稳定性演化图像和二维速度场.测量结果揭示了不稳定性流场的典型特征和细微结构,与高速摄影和数值模拟结果符合,说明建立的PIV技术适...     

多光谱成像的粒子图像测速

基于时间分辨的粒子图像测速技术(time-resolved particle image velocimetry, TR-PIV)是一种广泛应用的非接触式二维瞬时流场可视化测量技术。为了得到流场精细的瞬态空间结构和演变过程,提出了一种利用多光谱成像技术来提高流场测量的时间分辨率的方法。利用多个不同波长的脉冲激光照明流场中的同一测量区域,使用多光谱成像系统采集不同波长的粒子图像,经过图像分离,判决计算产生速度矢量场。为了验证这一原理的可行性,使用三种不同波长(488,532和632.8 nm)的单色光谱脉冲搭建了一套基于多光谱成像的TR-PIV系统,通过多波长激光脉冲之间时序的精确控制,将两帧图像之间的时间间隔从10 ms缩短至3.4 ms,时间分辨率提高了3倍。结果表明基于多光谱的TR-PIV测量系统在保持PIV技术瞬时全场测量特点的同时,时间分辨率大为提高。     

扩散燃烧流场的PIV测试方法探讨

由于能提供高时空分辨率的瞬时流场信息,二维粒子成像速度仪(PIV)已广泛应用于燃烧流场的测量.本文利用PIV对甲烷同轴射流扩散燃烧的流场进行了测量,针对测量中出现的示踪粒子导入、火焰发光干涉、光强不均、数据处理等问题进行了分析和实验,获得了有效的解决办法和满意的测量结果.     

多通道瞬态全息粒子场测量

采用光学多通道方法进行粒子场的全息拍摄,可以有效地减小相干噪音的干扰,同时极大地提高了对粒子场的层析能力,对于粒子大小为100μm下的粒了场层析能力能达到1mm。前后粒子之中可以互不干扰,便于准确地测量粒子的大小、运动方向和速度等。文中进行了理论分析和实验,结果较好。     

空气击穿效应对粒子全息像的影响

 在粒子场全息实验中,研究了4F光学成像系统不抽真空时,其内部实焦点处由于光脉冲能量聚焦引起的空气击穿现象。发现在这种情况下得到的同轴和离轴全息粒子再现像,与实焦点未被击穿时得到的正常全息再现像相比,其强度分布发生了反转。理论分析表明,这种情况是由于实焦点处空气击穿引起的空间滤波效应造成的。研究发现:在离轴粒子场全息实验中,合理调整曝光强度,利用4F系统中的空气击穿效应可以获得高清晰度的全息再现象。     

Digital particle holographic system for measurements of spray field characteristics

A digital particle holographic system for measurements of spray fields is presented. A double exposure hologram recording system with a synchronization system for time control is established, resulting in digital holograms that can be quickly recorded. To process recorded holograms, the correlation coefficient method is used for focal plane determination of particles. To remove noise and improve the quality of holograms and reconstructed images, a Wiener filter is adopted. The two-threshold and image segmentation methods are used for binary image transformation. For particle pairing, the match probability method is adopted. The proposed system is applied to a spray field, and three-dimensional velocities and sizes of spray droplets are measured. Measurement results from the digital holographic system are compared to those made by laser instruments, which prove the feasibility of the proposed in-line digital particle holographic system as a good measurement tool for spray droplets.     

激光辐照柱体铝靶的三维光滑粒子流体动力学仿真

在现有光滑粒子流体动力学方法基础上,提出了结合差分方法处理激光辐照边界条件的方法,并利用此方法自编程序模拟计算了功率密度为5.0109 W/cm2的强连续激光辐照铝靶时的热-力学效应,准确给出了与激光作用的边界粒子的分布和飞散情况,同时给出了不同时刻靶体的温度场,得到了温度分布规律,并对结果进行了分析。     

Laser-based volumetric colour-coded three-dimensional particle velocimetry

We present a method of three-dimensional particle velocimetry with a single digital colour camera using multiple colour illumination to encode image depth over a large volume. A copper vapour laser operating at 511 nm is used to pump an optical fibre producing a multiple-wavelength beam via multiple order stimulated Raman scattering. The beam is dispersed and formed into a stack of thin sheets to illuminate a volume of space. The spatial co-ordinates of particles imaged within the illuminated volume are obtained from their imaged x,y positions with depth discerned from particle hue (set by the wavelength of illumination). The method exhibits an RMS depth error of 3% in relation to the thickness of the illuminated region. This paper reports a proof-of-principle of three-dimensional particle imaging using a multi-wavelength laser source with a view to 3D-3C particle velocimetry.     

Three-dimensional particle imaging by wavefront sensing

We present two methods for three-dimensional particle metrology from a single two-dimensional view. The techniques are based on wavefront sensing where the three-dimensional location of a particle is encoded into a single image plane. The first technique is based on multiplanar imaging, and the second produces three-dimensional location information via anamorphic distortion of the recorded images. Preliminary results show that an uncertainty of 8 microm in depth can be obtained for low-particle density over a thin plane, and an uncertainty of 30 microm for higher particle density over a 10 mm deep volume.     

气管支气管树内气流和颗粒运动的大涡模拟

为更精确地描述真实人体呼吸道内的空气流动,明晰颗粒的运动沉积规律,本文从直接医学CT扫描得到的原始数据出发,利用图像辨识技术,重构了一个男性真人气管支气管树前三级的三维几何模型.采用大涡模拟的方法计算了非规则几何曲面结构内的气体流动现象,并在拉格朗日框架下跟踪颗粒的运动规律.数值计算得到了气流场的三维分布,以及颗粒的运动轨迹情况,结果表明现有基于Weibel的对称模型与真实人体的几何结构有较大的差异,而几何结构对流动影响较大;受非对称复杂结构影响,在不同截面的二次气流速度的分布规律不同;分叉后颗粒进入左右支气管的数量有明显的不同.     

频域稀疏采样和激光成像方法

激光的单色性和自然图像频谱稀疏且集中在低频区间的特点,使图像频谱稀疏采样成像成为可能.基于小规模激光探测器,引入参考激光,本文提出了频域稀疏采样激光成像方法.介绍了频域稀疏采样激光成像的原理和成像系统结构,推导了激光回波重构复频谱的表达式,给出了重构频谱和复图像的仿真结果并分析了信号参数对重构效果的影响,同时采用相干系数、均方误差和结构相似度来评价其重构效果.规模为256×256的激光回波复图像仿真表明, 5个拼接1/4×1/4规模频域探测器组成的近似十字型稀疏采样结构,在约31.25%(5/16)的频域稀疏采样条件下,仍可获得较好的重构频谱和重构复图像.     

纳秒脉冲激光对金属丝电爆炸过程的瞬态测量方法研究

金属丝电爆炸是获取金属纳米级粉粒的有效途径,电爆炸的演绎过程直接影响金属粉颗粒的尺度范围。采用纳秒级脉冲激光对爆炸过程的瞬态进行观察,以激光干涉条纹为背景,依据电爆炸过程中,对条纹的扰动获取具有清晰边缘的爆炸区图像;再根据激光穿过爆炸云团的透过率计算出不同时刻粉尘体浓度的三维分布图。测量结果表明:通电后0.5 μs,金属丝直径由0.3 mm扩展为4.7 mm, 直到18 μs时扩展为28 mm,而粒子的最大浓度由3×1021/cm3减小为1.1×1020/cm3。整个扩展过程中,粒子浓度沿径向呈现多个环带的分布形态。     

Holographic particle image velocimetry (HPIV)

There are several well-known difficulties in forming and analysing holographic particle data in the micrometre and sub-micrometre size range. This paper suggests that these problems can be overcome by using a combination of research techniques. Firstly, it has been found that it is possible to record images of sub-micrometre particles using conventional photographic materials. Essentially, a diffraction limited optical component has been used to provide aberration free particle images. Secondly, the sensitivity of the holographic material has been increased with the use of specialized holographic processing chemicals. Thirdly, it has been found that it is possible to encode holoraphically double, slightly displaced, particle images using a pulse laser. Thus, Young's fringes can be obtained directly from the stored holographic data and the particle velocity can be measured directly from the hologram. Fourthly, the holographic particle data can be automatically analysed using a software programme. Finally, since the data is stored holographically, it is possible to obtain instantaneous three-dimensional particle velocity. This paper demonstrates that it is possible to perform holographic particle image velocimetry automatically, with only a small amount of pre-processing.     

A real-time video encoded particle imaging tracking technique for velocity measurement

A real-time video encoded particle imaging tracking technique (VPIT) for velocity measurement has been developed. It can currently capture images of a seeded particle flow field at up to a video rate of 25 pictures per second. The method as shown in this paper is suitable for measuring a slow sparsely seeded flow. A VPIT image presents a triplet image pattern. The image has been encoded into a single video frame with the time history of three events. This is achieved by synchronising the video (CCIR) signal from a CCD (charge coupled device) camera, operating in frame integration mode with a suitable light source. The principle of VPIT demonstrates how the direction and the magnitude of the velocity can be recorded for a sequence or track of particles. The VPIT triplet images resolve several common difficulties associated with the application of PIV. Firstly, the time history of the laser pulse can be ‘labeled’ on an individual particle image. Secondly, there is no velocity direction ambiguity in the VPIT image. Thirdly, it is possible to extract the acceleration of the particle from a single VPIT frame. Finally, for a sequence of captured frames, the problems of particle path tracking are simplified, because each VPIT image has a video encoded time sequence ‘labelled’ on it.