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In the steam generator of the fast breeder prototype reactor "Monju", heat exchange tubes of helical coil type are utilized. Steam-water two-phase flows in the helical coil tube have unique characteristic due to effects of centrifugal acceleration. In this paper, we visualized gas-liquid two-phase flows in each the helical coil tubes with two curvature radii to investigate the effect of centrifugal acceleration, and also the slug flow in parallel helical coil tubes with same pressure condition at outlet part are visualized.

Bubble-Bubble interaction in a free-rising bubbly flow is measured with three-dimensional Particle Tracking Velocimetry (3-D PTV). The present report mentions the dependency of the interaction pattern on Reynolds number of rising bubble from 5 to 75. With the measurement data, it has been newly found that high Re number bubbles had repulsive motion each other both in horizontal and vertical direction as the distance of bubbles was shortened. The technique of PTV for extracting accurately the 3-D velocity vectors of bubbles is also discussed.

気泡流中では気液二相が互いに異なる流場を持ち，その相対速度は，気泡の並進運動特性によって支配される．近年では低Re数気泡の運動方程式モデルはほぼ確立されており，原理的に，気泡の速度ベクトルデータから液相流場を逆算することが可能である．本研究では，気泡速度ベクトルから，気泡軌跡近傍の液相速度ベクトルを逆算する手法と，その時空間的補間スキームの組み合わせにより，液相の流場を詳しく推定するアルゴリズムを提案した．このようなアルゴリズムは，トレーサ粒子を大量に散布できない工業機器や自然環境計測において利用が期待される．本論文では，気泡の並進運動に関する周波数解析から気泡運動からの推定の合理性を示したうえで，Taylor-Greenの渦流れを用いて提案したアルゴリズムの解析的評価について論じた．また，実際の気泡画像に対する実験的デモンストレーションにより，その実用性を明らかにした

Accurate postprocessing methods are required in order to analyze the detailed flow structures from the scattered data of particle-tracking velocimetry (PTV). In particular, vorticity distributions and stream functions are not reasonably obtained by conventional methods. This paper proposes a new postprocessing algorithm based on ellipsoidal differential equations; this method utilizes data as discrete boundary conditions. The results obtained by the proposed algorithm fully satisfy the equation of continuity and simultaneously correspond well with the raw data. The performance of the algorithm is examined by applying it to two-dimensional vortex flows and isotropic turbulent flows. The results reveal that the present algorithm has the highest accuracy among several conventional methods for detecting vorticity and streamlines.

Our previous study confirmed that ellipsoidal differential equations can be used to interpolate particle tracking velocimetry (PTV) measurement results. In the preset study, we deal with extensions of the equations; to time serial processing and to the detection of mismatched vectors. The performance of these algorithms is evaluated by using the flow around a rectangular cylinder and a vortex flow. Furthermore, the actual advantages of utilization of these methods are discussed by applying them to the experimental result of sudden vortex generation due to the collision of a circular cylinder with a flat wall.

In the steam generator of the fast breeder prototype reactor “Monju”, heat exchange tubes of helical coil type are utilized. Steam-water two-phase flows in the helical coil tube have unique characteristic due to effects of centrifugal acceleration. In this report, we visualized gas-liquid two-phase flows in the helical coil tube for providing the flow pattern map, and suggested the method for reconstructing the interfacial structures of gas-liquid two-phase flows in the cross-section of the tube. The method was applied to artificial images and experimental images, and the applicability was discussed.

Hybrid simulation techniques integrating time-resolved PIV with unsteady CFD can provide i) a set of flow quantities satisfying the governing equations temporally and spatially ii) possibly including unsteady pressure fields iii) with resolution comparable to CFD and iv) noise levels substantially lower than those of the original PIV data. We compare hybrid algorithms combining PTV (particle tracking velocimetry) and DNS with three different degrees of fidelity: the POD–Galerkin-projection approach, the proportional feedback of time-resolved PTV data, and the feedback based on the extended Kalman filter. By solving a planar-jet problem as an example, we analyze the temporaland spatial-filtering functions as well as the accuracy of velocity and pressure fields reconstructed from the PTV data. The results demonstrate that we can lower the measurement-noise levels and improve the accuracy/replicability by increasing the computational cost.

A new method called direct measurement of vorticity (DMV) for digital particle images is described in this paper. Unlike previous methods for calculating the vorticity in particle image velocimetry (PIV), the vorticity is determined directly from the average angular displacement of rotation between two matched patterns. In order to improve the stability and precision of the angular displacement, polar coordinates are used instead of Cartesian coordinates to depict gray level patterns. The results of a Monte Carlo simulation of an Oseen-vortex flow indicate that the accuracy of the DMV method is independent of the spatial resolution of the velocity sampling, and the errors in the velocity field will not be propagated into the vorticity field as occurs with some finite difference methods. Therefore, the DMV method is a good method to be used to extract the vorticity field from velocity data that has higher levels of uncertainty.

This paper describes a method for simultaneously measuring the velocities and sizes of falling particles. The measurement method consists of two parts. One is the recognition of the particles from a raw image by an image-processing technique in order to obtain the sizes and positions of the particles, and the other is a measurement technique of Particle Tracking Velocimetry based on fuzzy logic for the falling velocities of particles. The method is examined by a numerical experiment with computer-generated images. The result shows that the present method can be applied on-line for real-time processing of practical measurements.

A method for measuring the instantaneous 3-D bubble distribution in bubbly flows is proposed by making use of stereoscopic image processing. The method applies to the case of higher rather than dilute void fractions, because it is based on the following two statistic-based procedures. The first process is to obtain the 2-D distribution of local void fraction from visualized images, where a correlation between the bubble shadow fraction and the projection void fraction is derived by introducing the new idea of overlapping probability of the bubble-images under various conditions. The second process is to reconstruct the 3-D distribution of the local void fraction. In this step, a logical method is proposed in order to obtain the bubble-existence probability function which simultaneously satisfies the two distributions of the two projection void fractions. The present method is applied for instantaneous measurement of the 3-D structure of a bubble plume. The measured results show its particular structure, such as the hollow distribution of the bubbles, and the local spiral structure, which cannot be captured by point-measurement experiments.

Velocity vectors obtained by PTV are distributed discretely depending on the number density of tracer particles seeded in a flow. Especially, 3-D PTV obtains smaller number of data in 3-D space compared to 2-D PTV In order to extract physical properties such as streamlines, voracity contour and so on, velocity vectors have to be rearranged in grid space. This paper shows the applicability of post-processing methods based on ellipsoidal equations for PTV data in three-dimensional unsteady flows. Performance of the algorithms was examined with Hill's spherical vortex and PIV standard images by VSJ. As a result, it is recognized that these algorithms are sufficiently available for three-dimensional unsteady flows.

In ordinary PTV (Particle Tracking Velocimetry), tracer particles with the good traceability have been used. However, in the field of multiphase flow, there are needs which want to analysis non-tracer particles, such as bubbles and particles with specific gravity differenced from working fluid and a large diameter. Therefore, it is necessary to discuss on the traceability of non-tracer particle. In this study, the traceability for these non-tracer particles is estimated by using Lagrangian method, which directly uses the translation momentum equation of a non-tracer particle. Also velocity vectors of working fluid for the non-tracer particle are obtained by inverse analysis, these force components acted on the non-tracer particle are shown.

Most particle-tracking velocimetry (PTV) algorithms are not suitable for calculating the velocity vectors of a fluid flow subjected to strong deformation, because these algorithms deal only with flows due to translation. Accordingly, it is necessary to develop a novel algorithm applicable to flows subjected to strong deformations such as rotation, shear, expansion and compression. This paper proposes a novel particle tracking algorithm using the velocity gradient tensor (VGT) which can deal with strong deformations and demonstrates that this algorithm is applicable to some basic fluid motions (rigidly rotating flow, Couette flow, and expansion flow). Furthermore, the performance of this algorithm is compared with the binary image cross-correlation method (BICC), the four-consecutive-time-step particle tracking method (4-PTV), and the spring model particle tracking algorithm (SPG) using simulations and experimental data. As a result, it is shown that this novel algorithm is useful and applicable for the highly accurate measurement and analysis of fluid flows subjected to strong deformations.

Particle tracking velocimetry (PTV) has recently been recognized as quite an effective engineering research tool for understanding multi-dimensional fluid flow structures. There are, however, still a number of unsettled problems in the practical use of PTV, i.e. the lack of generality of the PTV algorithm for various types of flows and the measurement uncertainty with respect to spatial resolution. The authors have developed a generalized PTV algorithm named the velocity gradient tensor (VGT) method in order to accurately track the tracer particles in a flow field with strong local deformation rates. The performance of the VGT method has already been examined for several simple flow fields, such as linear shearing and Taylor-Green vortex flows. In this paper, the applicability of the VGT method for complicated flows, which include a wide dynamic range in wavenumber, is quantitatively examined by simulation of Rankine vortex flows, Karman vortex-shedding flows around a rectangular cylinder and homogeneous turbulent flows, which are numerically solved by using the unsteady Navier-Stokes equations. The results show that the VGT technique, using only two frames to estimate velocity, performs better than does the four-frame PTV technique and has a remarkably higher tracking performance than those of typical conventional PTV algorithms.

The inverse energy cascade in bubbly flow is investigated by a numerical simulation using the Eulerian-Lagrangian model in which the governing equations are formulated with emphasis on the translational motion of bubbles in nonuniform flow. In this paper we are concerned with the validation of the numerical model and various parametric dependencies on the inverse cascade. The calculated results reveal that, 1) continuous growth of the spatial fluctuation scale in a bubble-induced flow is well predicted by the present numerical model and the results have a good analogy with the experimental results which were introduced in our first report, 2) the strong relationship between energy-decaying process and bubble-bubble distance interval is also identified by the present analysis, and 3) the slope of energy-decaying in the high wavenumber region depends on the kinematic viscosity of liquid, and that in the low wavenumber region depends on inhomogeneous buoyancy distribution which changes due to the bubble motion.

An experiment showed a quite strong effect of inserting a circular cylinder into a unform rising bubbly flow. Size of the dffected zone was more than several times as that of the cylinder. The purpose of present study is to elucidate the mecahnism of generating the two-phase convection using a numerical analysis based on Elulerian-Lagrangian model by which the bubble's bpundary condition on the cylinder can be treated accurately. The numerical results showed a good agreement with the experimental results and revealed the dependency of the flow on the void fraction bubble radius, blockage ratio as well as the bubble's bouncing condition on the cylinder surface.

The turbulence structure in a rising bubbly flow driven by bubble buoyancy has been analyzed using the Eulerian-Lagrangian model. A new method of calculating the two-way interaction between the dispersed bubbles and the liquid phase was proposed to accurately simulate the local fluctuations of liquid flow induced by bubble migration. The present two-dimensional simulation revealed that, (1) in the case of the larger bubble, the turbulence structure has the longer wavelength in the vertical direction, and, (2) the wave spectrum of kinetic energy of the liquid phase is sensitive to the average void fraction and the lift force of the bubbles.

This paper describes a new method to divide a planar curve into circular arcs in order to recognize the overlapped particles in an image. The segmentation is based on a new breakpoint detection method. An area correlation coefficient for two arcs is introduced to identify and cluster the arcs belonging to the same circle. The Least-Squares Method is applied to estimate the center of a circle and its radius. The present method is evaluated using a computer-generated sample image and real coal-ash images with heavily overlapped particles taken by an electron microscope. All the results showed that the present method is effective in recognizing the overlapped circles with high accuracy.

The inverse energy cascade, which is one of the important phenomena to enhance the large-scale flow instability in bubbly flow, is investigated by measuring a local two-phase flow structure driven by buoyant bubbles using particle imaging velocimetry (PIV). In PIV, the flow field of liquid phase is measured by separating an original image to respective phase images using a statistical thresholding method for separating image parameters of bubbbles and particles. The present results obtained in the case where the bubble Reynolds number and average void fraction are less than 30 and 1.5%, respectively, confirm the large energy decay with a slope index steeper than -5/3 in the log-log diagram of energy spectrum in a high wavenumber region. An important relationship between the energy spectrum and the bubble-bubble interval distance is also detected.

In this paper, a non-pulsating jet and a pulsating jet are researched experimentally and the experiment data are analyzed with a PTV (Particle Tracking Velocimetry) method. The velocity fields are measured accurately and efficiently with a PTV method based on fuzzy logic although the strong shear and turbulence appear in the jets. Based on the measured velocity fields, the distributions of mean velocity, mean vorticity, shear strain rate and kinetic energy are compared between non-pulsating and pulsating jets in order to analyze the different flow features between the two kinds of flow fields.

With a concise review on some basic and novel algorithms and methods for the techniques of particle-imaging velocimetry (PIV), the paper reports an application of the PIV techniques to the investigation of particle motion in a gas–solid two-phase spiral flow in a horizontal tube. Axial velocities of the transported particles are obtained. Some important features of particle motion governing high transportation efficiency of the spiral flow are revealed by investigating probability density distribution of particle locations in a pipe cross-section.

A new algorithm of Delaunay Tessellation Particle Tracking Velocimetry (DT-PTV in abbreviation) is proposed for tracking particles in images of a PIV system by making use of the Delaunay tessellation (DT). The algorithm is tested by using numerically simulated particle images. The calculation results based on DT are compared with those obtained by a conventional algorithm of Binary Image Cross-correlation method (BICC). The new algorithm shows higher performance of obtaining more identical particles in two consecutive images correctly with shorter computation time even if the images contain many particles. A further application of DT to elimination of spurious vectors is also discussed.

It is well-known that the efficiency of capturing velocity vector in 3-D PTV is much lower than in 2-D PTV due to the problems in particles' occlusion, stereo-matching process, as well as the resolution of the optical hardwares. A new method for particle tracking velocimetry by using a color illumination device with only one camera has been proposed in the present paper. The information of color gradation in the depth direction is employed to determine their 3-D coordinates and velocity components. This report describes the performance of the present method, which is examined by measuring the 3-D flow field of a simple rotating flow.

Flow induced by oscillating elastic blades in quiescent liquid is investigated using PIV (particle imaging velocimetry). Theoretical prediction and image-measurement of the bending blade motion ranging from zero to 60 Hz in frequency indicate that is has maximum amplitude in the second order resonance mode owing to large added inertia force. PIV measurement is performed to evaluate the agitation structure around the blade with order of 106 in Reynolds number which is defined using the frequency f, blade length L and kinematic viscosity ν by Re=fL2/ν. More than 600 velocity vectors are obtained between two consecutive images by using the Binarized-Image Cross Correlation algorithm. The present results reveal generation of intermittent convection in the region down-stream of the blade, that period is over 10 times as that of oscillating blade. Also, parametirc dependency of induced energy on blade-dimension and forced frequency is shown in this experiment.

The number of particles passing through the whole field of interest in a unit time, referred to as the articles particle number rate, cannot be measured accurately and easily by the conventional methods when the number density of particles is high. However, there are many demands for whole field measurement of the particle number rate in various industrial processes. The purpose of the present investigation is to develop a new method for measuring the particle number rate by introducing PIV (Particle Imaging Velocimetry). In the present work, particles coming out of a hopper, and then falling in air or water were treated. Images of the falling particles were taken by a high speed video camera. Particle velocities were measured by the PIV based on the Binary Image Cross-Correlation Method (BICC), and the particle number rate crossing a plane could be computed from the mean velocity of particles and the number of the particles in the image. The performance of the present method for measuring the particle number rate was evaluated by numerical simulations and experiments. The experimental results showed that the particle number rate of a cloud of particles could be measured with high accuracy by the newly developed methods. The measurement precision of the particle number rate depends on the number of sampling video frames. Several seconds of video frames can yield sufficient precision of the particle number rate. The present research can be applied to on-line measurement of particles in many industrial fields.

Underground water/gas transporting pipelines or cable-defective pipelines are important facilities of modern cities.Installation of such underground pipeline systems may be carried out by using underground digging machines with some trenchless techniques that can meet the requirements of minimum impact on the environment.In this paper, an underground digging method is introduced and discussed for transportation characteristics of dug soil.A distinct feature of the air transportation is that a special device is used for controlling the dug soil when it is sucked into a transportation pipeline by a vacuum pump.This transportation method is tested with sand, and the air-sand two-phase flow is measured by using visualization and pressure measurement.Visual observation with a video camera shows that air-sand plug flow is a flow pattern in the present transportation conditions.The pressure drop is discussed based on the visualization measurement.

Bubble curtain is expected to be a new type of oil fence because it can generate a strong and wide surface flow over the bubble generation system. However, the most suitable condition for the bubble generation system has not been investigated. In this work, the surface flow induced by the bubble curtain is measured by particle imagining velocimetry, and the parametric dependency on the gas flow rate, void fraction and bubble size have been made clear. Furthermore, the internal two-phase flow structure in the bubble curtain is discussed with the PIV measurement data.

We have developed the velocity gradient tensor method (VGT) which is a PTV algorithm. When the VGT method is used at particle points, we can simultaneously get both of the velocity vectors and velocity gradient tensor. It means that physical information can be directly extracted at particle points. The purpose of this study is to propose a new technique of the extraction of physical information at particle points from the velocity gradient tensor. The processing is applied to the vortex flow and PIV-Standard Image, the performance is examined from the precision for extraction of vorticity and stream function.

Water was injected vertically downward through a straight circular pipe onto a water bath contained in a cylindrical vessel. Three types of bubble dispersion patterns were observed with respect to the distance from the pipe exit to the undisturbed bath surface. When the distance was short, small bubbles were generated at the bath surface and they dispersed in the whole bath (type 1). On the other hand, when the distance was long, relatively large bubbles were generated and the bubble dispersion region was localized beneath the pipe exit (type 3). For an intermediate distance, the bubble dispersion patterns of the two types appeared simultaneously (type 2). We focused on types 1 and 3 and carried out LDV measurements to investigate the liquid motion in the bubble dispersion region. In the case of type 1, the mean velocity and turbulence characteristics were not affected by bubbles and agreed well with those for single-phase free jets, while the two characteristics for type 3 were influenced significantly by bubbles. The differences in the two characteristics between types 1 and 3 were found to be associated with turbulence production in the wake of bubbles.

This paper describes a new method to measure the sizes of particles and their probability distribution function by image processing. In the present research, an image with heavily overlapped particles was processed. The edges of the particles in the image are detected by Canny's method, and the contours are linked from the pixels in the edges by using chain-coding. The contours are subsequently segmented according to the curvature. Constant curvature segments are clustered according to some relations among contour segments which are likely to represent the same circle. The Least Squares Method which provides an accurate parameter estimation is performed to find out the parameters of a circle. The present method can recover most of particles even in a heavily overlapped particle image. It provides a useful way of investigating the structure of material or counting particles in many fields of engineering. Another advantage of the present method is its short computational time. All the computations in this paper were carried out on a personal computer, and the computational time of processing one image was between 4–10 sec on the personal computer (Pentium II, 300 MHz), which depended on the number of particles in the image. It is clear that the present research can be extended to the real-time processing of particle-detecting and particle-measuring in the future.

Velocity vectors obtained by PIV are distributed discretely depending on the number density of the tracer particles seeded in the flow. In order to estimate the detailed whole-field flow structure from the data, an estimation algorithm to restore the whole-field flow has been proposed using Laplace Equation and velocity correction potential. The performance of the algorithm was examined for two-dimensional vortex flow. The correct restoration rate was evaluated quantitatively by two-dimensional correlation coefficient for the stream function. The results reveal that the present method is applicable for various conditions of discrete PIV data to predict the whole-field flow structure.

This paper describes a method to separate and count the number of particles in an overlapped image. The edges in an image are detected by Canny's method, and contours are linked from the pixels in edges. Contours are segmented using a criterion based on the derivative of the curvature. Constant curvature segments are clustered according to the relations among contour segments which are likely to represent the same circles. A minimization criterion is used to find out the circle parameters that provide accurate parameter estimation. The method can recover many circles in a heavily overlapped particle image, and provide a useful way in some practical applications, such as counting particles, separating overlapped bubbles in PIV system.

Conditional sampling measurements were made to reveal the turbulence structures of a steady round jet and a pulsating round jet with low pulsation frequency and relatively large velocity amplitude using a hot-wire anemometer and a laser Doppler velocimeter. Turbulent motions were classified into four distinct categories : ejection, sweep, outward interaction and inward interaction. The fraction of time the velocity signals were in the respective categories and the contributions of each motion to the Reynolds shear stress and turbulence kinetic energy were determined. Ejection and sweep were found to be responsible for turbulence production. The correlation coefficient between the axial and the radial velocity fluctuations showed that large-scale ordered motions existed in the jet. There was little difference between the turbulent structures of the steady and pulsating jets.

Detailed information on the fluid flow around a bubble is required for better understanding of metallurgical reactions in the steelmaking processes agitated by gas injection. In the current research a model has been used for a cold simulation experiment of water-air two-phase flow. Previous studies have focused mainly on the time-averaged flow structure around bubbles. However, it is well known that the movement of a bubble is transient and three-dimensional, and hence, the flow around the bubble is also transient and three-dimensional. This study was carried out to elucidate the flow around a single bubble rising in a cylindrical water vessel.3-D PTV (Particle Tracking Velocimetry) is used to analyze the movement of gas-bubbles in the water bath. The water flow around a single bubble is investigated by the technique of PIV based on visualization and image processing. An experimental apparatus is set up to generate a bubble of known volume rising from bottom. Velocities of the bubble and the surrounding fluid are obtained simultaneously by a three consecutive time picture cross-correlation 3-D PTV. A new technique that can measure the fluctuating velocity field and ensemble averaged kinetic energy from the time series of particle imaging is developed in data processing.

In this paper, a new algorithm of particle identification based on Delaunay tessellation is proposed. Delaunay tessellation is a method which connects every scattered nodes to form triangles in either two-dimensional or three-dimensional space. Such a triangulation provides an essential step for spatial analysis of scattered data. Delaunay tessellation can be applied in PIV which deals with the particles in image. A new cross-correlation method for particle identification has been devised and tested by numerical simulation. Good result can be obtained.