基于PIV技术的静电喷嘴雾化参数优化

为了提高射流液体的雾化效果,在分析荷电作用下两相湍流数学模型的基础上,采用粒子图像测速(particle image velocimetry,PIV)技术优化影响静电喷嘴雾化能力的主要参数(液体压力和充电电压)。结果表明:随着液体压力的增大,喷雾粒度表现出明显的单调减小的变化规律;液滴雾化粒度在充电电压10~20 k V之间是变化较大;随着充电电压的增大,雾化角呈现先增大后减小的趋势。通过因素水平综合分析确定液体压力为4 MPa和充电电压在10~25 k V之间对静电雾化喷嘴的雾化效果是最有利的。     

基于PIV的大豆蛋白液双枪喷涂速度场的研究

目的 为了在保证喷涂雾化表征均匀性的前提下实现宽幅覆膜,提高覆膜的效率,以期得到均匀一致的大豆蛋白覆膜。方法 利用粒子图像速度场仪（Particle Image Velocimetry,PIV）,对不同干涉程度下的大豆蛋白液双枪喷涂雾化场进行拍摄,利用PIV和Origin软件处理图像,得到速度数据并对比。结果 随着双枪间偏转角的增大,基线上的平均速度减小;偏转角为0°时,两喷雾粒子流在干涉线处碰撞,少有透过干涉线的粒子;在不同偏转角下,基线上的速度峰值从大到小为偏转角7°时的速度峰值、偏转角0°时的速度峰值、偏转角15°时的速度峰值;当偏转角为0°时,随着液压的增大,基线上的第2个速度谷值会右移,并且会增大直至消去。结论 当偏转角为0°、液压为0.24 MPa时,在基线上干涉区域内的速度最均匀。     

基于散焦的三维显微粒子追踪测速

为了开展三维显微粒子追踪测速研究,设计了一种孔边缘厚度0.1mm,距挡板边缘间厚度成线性分布的三孔挡板,搭建了一套高速显微散焦粒子三维测速系统.通过光学和图像分析得到了工作介质粒子散焦图像构型参数和粒子深度方向的标定函数,并用二元多项式拟合获得了关于粒子平面位置的补偿函数,实现了粒子空间位置的识别和追踪.还针对倒置台阶结构的微通道流动进行了测量,采用20×0.4显微物镜和高速CMOS相机对通道内部播撒的2μm的荧光粒子进行了追踪,获得了粒子运动轨迹及三维速度分布.最后,采用数值仿真方法进行了验证,结果表明所搭建散焦测速系统和算法具有可行性和有效性.     

图像测速法的摄像机标定技术

针对漂浮在空气中或者液体中的粒子的速度测量,提出了一种基于双目视觉的测量方法。采用两个光轴相互垂直的CCD摄像机,分布在测量腔体的左右两侧。结合系统的几何结构特点,两个CCD摄像机分别标定,将标定模型方程转化为多项式形式,利用最小二乘原则获取平面模型标定参数,然后再利用公垂线距离最短原则实现三维坐标测量。实验给出了三维坐标的偏差分布图,证明这是一种实用有效快速的标定方法。     

大豆蛋白液喷涂粒子速度场的PIV初探

目的选择蔬菜复合纸覆膜成型过程中的最优喷涂条件。方法利用PIV(粒子图像测速)技术测量不同喷涂参数下大豆蛋白液喷涂雾化粒子的速度场分布,并通过数据分析软件Tecplot处理分析喷涂参数对大豆蛋白液喷涂雾化粒子速度场的影响,最终得出喷雾速度场中心轴上和某一截面上速度的变化规律。结果当喷涂气压一定时,喷涂粒子速度随着喷涂液压的增大呈增大趋势,但不是很明显。当喷涂液压不变时,喷涂粒子速度随着喷涂气压的增大呈先减小后增大的趋势。在喷雾场喷嘴中轴线方向上雾化粒子速度从喷口喷出后先急剧增大,随着距喷嘴越来越远逐渐呈现波动变化的趋势,最后趋于稳定。在距离喷嘴300 mm的截面处,粒子速度以轴心处最大,向外沿径向逐渐减小,大体呈对称趋势。结论用PIV技术对大豆蛋白液喷涂粒子速度场进行研究,可为后期蔬菜复合纸覆膜成型提供一个有力的试验数据参考。     

聚合物真实黏度流变仪收缩流道轴向速度场的PIV实验研究及分析EI北大核心CSCD

为研究测量聚合物真实黏度流变仪收缩流道轴向速度分布规律,建立了收缩流道实验模型及实验方案。利用粒子图像测速(PIV)系统拍摄牛顿流体聚丁二烯在收缩流道流场中粒子的图像,利用Tecplot、Origin软件对图像和数据进行分析处理,得到聚合物真实黏度流变仪收缩流道的轴向速度曲线。同时将PIV实验、Polyflow仿真、理论计算结果相比较,发现三者规律基本吻合。证明了从PIV实验中得到牛顿流体聚丁二烯收缩流道速度场的方法是可行的。     

粒子图像测速技术测量精度影响因素分析

对基于粒子图像测速(PIV)技术的瞬时全流场测量方法进行了综述.系统介绍了 PIV的工作原理、技术的关键环节(获取图像的品质)和影响测量精度主要因素(示踪粒子性能、光源性能、背景噪声、成像畸变、同步器时间分辨率及图像处理算法).基于这些分析,给出了示踪粒子性能的保障、成像组件的选择以及图像处理方法确定的具体建议.     

稀薄气体流动的粒子图像测速实验研究

建立了一套可对真空度进行调节的实验装置,从大气压开始逐渐降低系统压力,进行系列稀薄气体流动的PIV流场实验.系统压力从101kPa、90kPa逐次降至10kPa,使用所选粒子在不同系统压力下分别进行PIV实验获得测量区域流场分布情况.运用计算流体力学的方法模拟大气压条件下实验区域的内部流动,对比结果发现该种条件下数值模...     

基于PIV技术真空开关电弧流场实验研究

为了对真空开关电弧燃烧过程及热形态变化规律研究,本文采用粒子成像测速(PIV)技术对短间隙真空开关电弧进行了实验研究,观察分析了电弧流场的信息,有明显的漩涡区。实验结果表明,运用PIV技术能较好地获取真空开关电弧燃烧二维速度场分布;随着电弧电流不断增大,真空间隙中金属蒸气压力不断增大,电弧加速向四周扩散运动,当电弧电流增大到一定值时,在电弧四周产生明显的涡流区域;电弧电流峰值过后,涡流区域不断减小,当电弧电流减小到一定值时,电弧不再向外扩散,而是向弧柱中心做集聚运动。     

半封闭圆管冲击射流流动特性PIV试验研究

为研究封闭板对长直圆管冲击射流流动特性的影响,采用粒子图像测速技术对不同雷诺数Re(5 084～13 926)和冲击距H/d(2～6)条件下的流场进行了测量,统计分析了回流区运动规律、势流核长度变化、射流冲击前卷吸特性、壁面射流扩展率及速度衰减指数.试验结果发现:①雷诺数和冲击距对回流区运动特征的影响规律与半封闭孔板冲...     

Particle migration of concentrated suspension flow in bifurcating channels

Flow of suspension in bifurcating channels has extensive applications in industrial and natural settings. A phenomenon of particular interest during the flow of concentrated suspension is shear-induced particle migration. Previous works on suspension transport in branched channels have been limited to dilute flow conditions. We have carried out experiments using the Particle Image Velocimetry (PIV) technique to study concentrated suspension transport in asymmetric T- and symmetric Y-shape channels. Numerical simulations of fluid flow and particle transport equations were also carried out for the same geometry which was used in the experiments. The migration and transport of particles in the simulations were studied using the Diffusive Flux Model. We have observed in both experiments and numerical simulations that due to the shear-induced migration phenomena the particles move towards the center of the channel, and this gives rise to the blunting of velocity profile before the junction. After the bifurcation, the peak of velocity profile moves in the direction of the outer wall, whereas, the maxima in particle concentration was observed near the inner walls. This causes asymmetry in the velocity and concentration profiles in the daughter branches. As we move towards the downstream positions the maxima in velocity and concentration profiles again shifts toward the center of the channel. The results from the experiments and simulations are observed to be in good agreement.     

Tomographic particle image velocimetry of desert locust wakes: instantaneous volumes combine to reveal hidden vortex elements and rapid wake deformation

Aerodynamic structures generated by animals in flight are unstable and complex. Recent progress in quantitative flow visualization has advanced our understanding of animal aerodynamics, but measurements have hitherto been limited to flow velocities at a plane through the wake. We applied an emergent, high-speed, volumetric fluid imaging technique (tomographic particle image velocimetry) to examine segments of the wake of desert locusts, capturing fully three-dimensional instantaneous flow fields. We used those flow fields to characterize the aerodynamic footprint in unprecedented detail and revealed previously unseen wake elements that would have gone undetected by two-dimensional or stereo-imaging technology. Vortex iso-surface topographies show the spatio-temporal signature of aerodynamic force generation manifest in the wake of locusts, and expose the extent to which animal wakes can deform, potentially leading to unreliable calculations of lift and thrust when using conventional diagnostic methods. We discuss implications for experimental design and analysis as volumetric flow imaging becomes more widespread.     

基于CFD的搅拌流场模拟及预测研究

为研究叶片数、挡板、转速3个因素对搅拌釜流场的影响及对搅拌釜内流场速度进行预测,运用Fluent软件中的多重参考坐标系法（MRF）处理搅拌桨区,从叶片数、挡板及转速3个角度对搅拌釜流场进行模拟,并对结果进行拟合分析。结果表明,有挡板的流场比无挡板时发展更充分,6叶片的流场比4叶片时更加均匀;有挡板时的速度高于无挡板时的速度,在远离桨叶端6叶片的速度大于4叶片的速度。对z=0及y=0截面上的速度进行拟合,得到釜内流场流速的预测公式,对实际流场的研究具有一定的参考价值。     

基于光流场技术的复杂背景下运动目标跟踪

针对光电经纬仪在飞机起飞着陆段跟踪角速度大、背景复杂的情况,根据小波多分辨率技术,提出利用小波分层组成低频图像金字塔,利用光流技术进行匹配解算,实现由粗到精的特征点匹配跟踪。通过对飞行试验视频图像进行事后自动跟踪试验,结果表明,该算法能够稳定可靠跟踪多特征点目标,具有鲁棒性。     

Inviscid transonic flow field analysis

This paper describes a method for analysing inviscid transonic flow. This method is based on the fact that the angle made by the streamline of the transonic flow and of the corresponding incompressible flow is usually small. By using curvilinear coordinates, the differential equation of the stream function of an inviscid compressible flow is simplified and a general solution of the equation obtained. As examples of the method, transonic solutions are given for flow through twodimensional and axisymmetric Laval nozzles of different throat wall radii together with sonic lines and iso-Mach lines. To determine the discharge coefficients of Laval nozzles, an integral relation is developed. The general behaviour of the transonic flow in the throat region is presented, and the effect of the mass discharge on the Mach number distribution in the nozzle analysed. The effects of the ratio of the specific heats on the characteristics of the flow in the throat region are discussed. For transonic flow around a circular cylinder and a sphere, sonic lines and iso-Mach lines are presented for free-stream Mach number varying from the subcritical to the supercritical, including a free-stream Mach number of one. Part of the results obtained are compared with those available in current literature. For the two-dimensional hyperbolic Laval nozzles, the iso-Mach lines are compared with those given by Cherry (1959) and Serra (1972). For, axisymmetric Laval nozzles, the discharge coefficient and the Mach number at the throatsection for various throat wall radii are compared with those given by Sauer (1944), Hall (1962), Kliegel & Levine (1969), and Klopfer & Holt (1975). The theoretical discharge coefficients are compared with the experimental results by Backet al (1975), Durham (1955), Norton & Shelton (1969) etc. For the transonic flow around a circular cylinder, the iso-Mach lines are compared with Cherry’s exact solution for the quasi-circular cylinder for.M∞ equal to 0.51. The. Mach number distributions on the surface of the circular cylinder are compared with those given by Imai (1941) forM∞ equal to 0.4, by Cherry (1947) forM∞ equal to 0.51, by Dorodnicyn (1956) forM∞ equal to 1, and by Hafez, South & Murman (1979) forM∞ equal to 0.51. The present method has a much wider scope of application, requires simpler computation and gives results with good accuracy. It is being used to analyse supercritical wings and cascades, and we expect to extend its application to the field of transonic unsteady flow.     

Alternative approach for defining the particle population requirements for static image analysis based particle characterization methods

For image based particle characterisation approaches one of the most common discussion points is determining the number of particles required to have statistical confidence that the measurement is able to adequately describe the distribution of the sample. This topic becomes significantly more challenging when applied to the extraction of single component size distributions from multi-component samples.The aim of this work was to propose a means to accurately assess the particle number requirements using a method specific approach. The method applies a sub-sampling method to the original imaged dataset in order to provide an understanding of the impact of sub-sampling on the ability to accurately reproduce the original distribution.The method was applied to understand the particle number requirements for two batches of theophylline anhydrous with varied particle size distributions, using the input size distribution to guide the requirements for the subsequent multi-component samples of both materials.The results demonstrate the utility of the method to determine the appropriate number of particles required to recreate the size distributions. Whilst the minimum number of particles required to be sampled can be estimated, how those particles are sampled can also affect the validity of the measurement and must be taken into consideration.     

非均匀背景下的红外图像曲面拟合分割

红外图像往往存在着背景不一致的特点,因此在分割时无法有效地提取出目标。本文针对这一问题提出了一种基于曲面拟合的图像分割方法,以分割非均匀背景下的红外目标。这种方法首先对背景进行光顺限制的曲面拟合,再通过设置一个偏移量来形成阈值曲面。通过研究发现,曲面拟合时的偏离项和光顺项的权重系数比是由图像背景的双拉普拉斯变换以及噪声均方差共同决定的,从而在估计噪声均方差的基础上实现了对权重系数的自适应选取。从仿真结果可以看出,本文提出的曲面拟合分割法在背景去除和目标提取上要优于传统的Ostu法和局部阈值法。     

Relative assessment of full field experimental stress analysis techniques

There is an array of full field experimental stress analysis techniques available to aid the designer or the engineer investigating service failures. This note reviews currently available methods (i.e. photoelasticity, moiré, laser holography, brittle lacquer and SPATE) and assesses their relative merits in practical applications.     

大型高度-温度试验舱分布式送风流场仿真及分析

针对大型高度-温度试验舱在低气压环境下试验空间内温度场均匀性下降的问题,通过对大型高度-温度试验舱分布式送风流场进行数值仿真及分析,研究了两种不同送风方式下低气压试验舱内的温度场变化规律。结果表明,试验舱内温度场均匀性随着环境压力的降低而下降;增加试验舱内壁辐射换热、提高流场风速,均可以提高试验舱内的温度均匀性;同样环境压力下,采用双侧送风方式比单侧送风方式的试验舱内温度场均匀性更好,但平均风速较高。在进行高度-温度试验舱设计时,需根据不同的试验需求选择不同的送风方式。     

Three-dimensional measurement of a gas flow temperature field using far-infrared band CT techniques

Emission spectral tomography (EST) can be utilized to reconstruct three-dimensional (3D) physical parameter distributions of gas flow fields. Mostly, the radiant energy of the visual and near-infrared bands is received by a video camera in EST, so it is difficult to examine a low/medium-temperature gas flow field by normal EST. However, the far-infrared radiant energy of a low/medium-temperature gas flow field is strong enough to be received by a far-infrared detector. Based on EST, a far-infrared band computed tomography (FICT) approach is proposed that focuses on far-infrared spectral emission and band emission tomography. Both low- and medium-temperature blackbody furnaces were adopted to calibrate the relation between infrared thermal image intensity and radiant exitance. The 3D temperature reconstruction of an alcohol blow lamp was carried out. According to the results of multiple measurements, the relative error of the FICT approach is less than 20%. The experimental results prove the feasibility of the FICT approach.