共查询到20条相似文献,搜索用时 15 毫秒
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The combination of the optical diagnostics and image processing technique has produced various methods of practical measurement in engineering. The measurement of size and velocity of droplets in fuel spray is one typical example. In general, the spray is a complicated and three-dimensional two-phase flow; therefore multi-dimensional field measurement of the spray field is indispensable. In the present paper, a technique of simultaneous measurement of droplet size and three-components of velocity is proposed and applied to spray issuing from the swirl nozzle as a practical application. The focused image of glare points is captured by a stereoscopic arrangement, and droplet size and the three-components of velocity are evaluated from the doublet image. Fundamental optical arrangements to capture the image of the glare points with a stereo view are established, and the feasibility and the accuracy of the technique are confirmed. © 2004 The Optical Society of Japan 相似文献
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Jeronimus P. A. J. van Beeck Michel L. Riethmuller 《Particle & Particle Systems Characterization》1997,14(4):186-192
A rainbow measurement technique is presented which measures simultaneously the size, temperature and velocity of individual droplets in a spray. The technique is based on rainbow interferometry in combination with diffraction by a wire placed in the spatial filter of the scattered-light detector. A photomultiplier detects the wire diffraction pattern superimposed on the rainbow interference pattern created by a droplet scattering laser light. The velocity is determined from the equivalent geometric wire shadow. The necessary sphericity validation is performed by comparing the Airy and the ripple droplet diameters, resulting from the respective interference structures. The temperature is recovered from the position of the wire diffraction pattern relative to the main rainbow maximum. The technique was applied to a water spray at ambient temperature. The results showed the importance of nonsphericity detection. 相似文献
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气液两相流速度及粒径分布激光干涉测量方法的研究 总被引:1,自引:0,他引:1
为了实现对气液两相流的粒子粒径、空间分布及其速度测量。对激光干涉气液两相流测量技术(ILIDS)进行了深入研究,该技术是一种应州于气液两相流测量的新技术,其主要优点是不干扰流场和颗粒粒径、位置测量精度高。基于该技术所开发的图像自动处理方法可以利用普通粒子成像测量技术系统拍摄气液两相流的激光散射干涉图像。并利用图像卷积定位、傅里叶变换频率分析及其图像互相关测速等图像处理手段从干涉图像中自动提取粒子的位置、直径和速度信息。为了验证该方法的测量精度,对喷嘴生成的气水两相流进行了测量实验,得到了喷嘴出口处不同区域的粒径、速度矢量的空间分布,并将测得的速度矢量与用粒子成像测量技术方法测得的结果进行对比,证明两种方法测量的平均速度差别仅为0.38%。 相似文献
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Christine Mounaïm-Rousselle Olivier Pajot 《Particle & Particle Systems Characterization》1999,16(4):160-168
A theoretical explanation is given of a technique based on Mie scattering interferometry (MSI), obtained by defocusing of the collecting optics, to size droplets. The originality of this study is the development of a droplet sizing method by planar laser light scattering for the case of a scattering angle range close to 90°. The feasibility of this method and its limitations are fully described. The dependence on intensity levels and refractive index variations can be neglected. After discussion of some practical details about particle size, imaging and camera constraints, the results obtained in the combustion chamber of a spark ignition (SI) engine, near the spark plug, prior to ignition and for different injection timings are described and discussed. It can be concluded that the implementation of the MSI method in this experimental set-up has been realized successfully to provide droplet distributions in an SI engine. To allow the easier use of the technique, image processing software will be developed in the Matlab environment. 相似文献
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Frank Schne Klaus Bauckhage Thomas Wriedt 《Particle & Particle Systems Characterization》1994,11(4):327-338
Measurements of particle size distributions in multi-phase flows with a phase-Doppler anemometer yield incorrect results if polydisperse particles are investigated. For weighting biased size distributions, different in situ methods, requiring the size of the detection area, are known, but all of these weighting procedures are restricted to very small measuring volumes if off-axis instrument configurations are considered. Moreover, the weighting functions have some disadvantages in the case of poor statistics in single size classes or the results are not suitable for determining the size of the detection area for particles which are larger than the beam waist. Therefore, the intention in this work was to measure the size of the detection area for different kinds of monodisperse particles, different instrument configurations and varied instrument sensitivities experimentally and to develop an improved weighting procedure that copes with the above difficulties. The application of the results obtained from the investigations with monodisperse particles to measured particle size distributions and volume flux densities of polydisperse water droplets in a spray cone of an atomizer confirms the applicability of this weighting procedure. It is still restricted to directed flows, perpendicular to the fringes. 相似文献
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An image analysis technique has been developed in order to determine the drop size distributions of sprays produced by low‐velocity plain cylindrical jets. The particle sizing method is based on incoherent backlight images. Each drop is analyzed individually in the image. The two‐dimensional image resulting from the projection of the three‐dimensional object shape (the drop) on a screen (the video sensor surface) is modeled. The model, based on the point spread function formulation, has been developed to derive a relation between contrast and relative width of individual drops. This relation is used to extend the domain of validity of drop size in terms of size range, out of focus and image resolution. The shape parameter is determined for each drop image through morphological analysis. Spherical and non‐spherical droplets are then sorted on the basis of this parameter. Non‐spherical drops are regarded as non‐fully atomized liquid bulks or coalesced drops. Finally, the droplet size distribution of true spherical droplets is established for a low‐velocity plain cylindrical liquid jet. 相似文献
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Shack-Hartmann波前传感器用于闪烁和相位起伏效应的同时测量 总被引:3,自引:1,他引:2
将每一个子孔径及相应的CCD面元作为一个光强探测系统,可以将Shack-Hartmann波前传感器用于湍流大气闪烁效应的测量.分析了该测量方法的基本原理,并结合其波前探测的功能.在近地面水平1km的湍流大气中,同时进行了闪烁和相位起伏的实验研究.将闪烁测量得到的Cn2与大口径闪烁仪测量的结果进行对比,发现两者的相关系数达0.838,验证了Shack-Hartmann波前传感器用于闪烁效应测量的可靠性.对闪烁和相位起伏效应得到的Cn2的日变化进行了对比.结果表明,两者在变化趋势上具有较好的一致性;采用双对数坐标对两种结果进行相关性分析,发现两者的相关系数达0.798.这表明将Shack-Hartmann波前传感器用于闪烁和相位起伏效应的同时测量是可行的,拓展了该传感器的使用功能. 相似文献
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Masanobu Maeda Hiroshi Morikita Ilias Prassas Alexander M. K. P. Taylor Jim H. Whitelaw 《Particle & Particle Systems Characterization》1997,14(2):79-87
We report the application of the Shadow Doppler Velocimeter (SDV) for spatial precise, simultaneous measurement of the size and velocity to assess the particle retention performance of a laboratory, 1/6 scale, 10 kW vertically-fired atmospheric model of the pressurised pulverised-coal furnace of Reichert et al. [1]. The SDV is based on the imaging of a conventional LDV probe volume onto a linear photodiode array and has the advantage over other sizing methods for irregular particles that it is tolerant of the optical misalignment and fouling which are inevitable when passing laser beams through windows in such furnaces. The size and two components of velocity of burning coal particles were measured in the present geometry which has 172 mm furnace diameter and 40 mm lateral exit duct diameter and a calculated exit bulk velocity of 4 m/s, evaluated at 300 K. The Sauter mean diameter of the particles is, within the experimental error, uniform at about 40 μm in the vertical profile normal to the axis of the exhaust pipe, 34.5 mm upstream of the exit. Coal particle velocities in the near-exit region are directed towards the exit, closely following the gas-phase velocities. Both these observations imply that particle retention efficiency due to streamline curvature is low and extrapolation suggests that there will be even less at large scales. 相似文献
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We use a derived incompressible modified Navier-Stokes equation to model pipe flow and wall turbulence.We reproduce the observed flattened paraboloid velocity profiles of turbulence that cannot be obtained directly using standard incompressible Navier-Stokes equation.The solutions found are in harmony with multi-valued velocity fields as a definition of turbulence.Repeating the procedure for the flow of turbulent fluid between two parallel flat plates we find similar flattened velocity profiles.We extend the analysis to the turbulent flow along a single wall and compare the results with experimental data and the established controversial von Karman logarithmic law of the wall. 相似文献
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We derive higher order magneto-hydrodynamic (MHD) equations from a microscopic picture using pro-jection and perturbation formalism. In an application to Hartmann flow we find velocity profiles flattening towards the center at the onset of turbulence in hydrodynamic limit. Comparison with the system under the effect of a uniform magnetic field yields difference in the onset of turbulence consistent with observations, showing that the presence of magnetic field inhibits onset of instability or turbulence. The laminar-turbulent transition is demonstrated in a phase transition plot of the development in time of the relative average velocities vs. Reynolds number showing a sharp increase of the relative average velocity at the transition point as determined by the critical Reynolds number. 相似文献
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Fabrice Onofri 《Particle & Particle Systems Characterization》1999,16(3):119-127
The principle of the optical technique critical angle refractometry, used to determine the size and refractive index of spherical particles (with relative refractive index below unity) in liquid flows, was investigated. This technique is based on the observation of the particle scattering pattern around the critical angle. Similarly to the recent technique developed for rainbow scattering pattern analysis for droplet temperature and size measurements, it is shown that the relative particle refractive index (mr<1) and size can be determined from the position of the primary diffraction fringe and from the angular spacing between two fringes. Explicit equations for refractive index and particle size measurement were derived from the first-order term of the physical optics approximation. An experimental validation test and numerical computations based on the Lorenz-Mie theory were used to validate the principle of the proposed technique and to estimate its sensitivity, which was shown to be of the same order as that of the rainbow technique. This technique is considered to be useful for various applications in liquid multiphase flows where the particles size and material are to be characterized. 相似文献
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LI Jing LIU Zhao-Hui WANG Han-Feng CHEN Sheng LIU Ya-Ming HAN Hai-Feng ZHENG Chu-Guang 《中国物理快报》2010,27(6):129-132
Turbulence modulations are experimentally investigated using particle image velocimetry (PIV) in the lower boundary layer of a fully developed horizontal channel flow. A simultaneous two-phase PIV measurement technique is adopted to acquire the turbulent statistics quantities and to examine the coherent structures in the near-wall region. Polythene beads with diameters of 60 μm are used as dispersed phases, and the PIV measurements have been performed at three mass loadings varying from 2.5 ×10^-4 to 5 × 10^-3. All the experiments are performed at a wall shear Reynolds number of Reτ = 430. The results show that the presence of the particles suppresses the coherent structures, with shorter streamwise extent of the quasistrearnwise structures, and then, the wall-normal velocity fluctuations and shear Reynolds stresses are both decreased in the near-core region. In addition, as a result of the particle wake, the turbulence intensity and shear Reynolds stress both increase in the vicinity of the wall. Due to the drag effects of the particles on the gas, the streamwise velocity gradients decrease in the outer region and increase in the viscous sublayer, meanwhile the thickness of the viscous sublayer also decreases. These results cause the peak values of the streamwise velocity fluctuations adjacent to the wall to increase, and the peak positions shift to the wall. This is the reason for decreasing the near-wall region and increasing the near-core region of the streamwise velocity fluctuations in appearance. 相似文献
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Steep variations in concentration and temperature frequently occur in small fluid compartments such as those found in cells or microfluidic devices. A quantitative characterization of concentration and temperature gradients is therefore required before these systems can be fully understood. Although different spatially resolved fluorescence methods have been developed to measure either the temperature or the concentration of ions such as proton or calcium, often concentration measurements depend on temperature and vice versa. Here, we describe a method allowing simultaneous measurement of pH and temperature. This method is based on the detection of the blinking of the fluorescent pH indicator pyranine, a process due to its alternating between a basic form and an acidic form. Fluorescence correlation spectroscopy allows measuring both the protonation and deprotonation rates of pyranine, and each pair of rates can be uniquely related to a pair of pH and temperature values. We show, however, that the relationship between rates, pH and temperature, is very sensitive to the presence of other acid-base molecules in solution. We also show that it is influenced by the overall ionic strength of the solution, in a manner that depends on buffer composition. 相似文献