The present work introduces an extension to three-dimensional Particle Tracking Velocimetry (3-D PTV) in order to investigate small-scale flow patterns. Instead of using monochrome particles the novelty over the prior...The present work introduces an extension to three-dimensional Particle Tracking Velocimetry (3-D PTV) in order to investigate small-scale flow patterns. Instead of using monochrome particles the novelty over the prior state of the art is the use of differently dyed tracer particles and the identification of particle color classes directly on Bayer raw images. Especially in the case of a three camera setup it will be shown that the number of ambiguities is dramatically decreased when searching for homologous points in different images. This refers particularly to the determination of spatial parti- cle positions and possibly to the linking of positions into trajectories. The approach allows the handling of tracer parti- cles in high numbers and is therefore perfectly suited for gas flow investigations. Although the idea is simple, difficult- ties may arise particularly in determining the color class of individual particle when its projection on a Bayer sensor is too small. Hence, it is not recommended to extract features from RGB images for color class recognition due to infor- mation loss during the Bayer demosaicing process. This article demonstrates how to classify the color of small sized tracers directly on Bayer raw images.展开更多
Particle tracking velocimetry(PTV)is one of the most commonly applied granular flow velocity measurement methods.However,traditional PTV methods may have issues such as high mismatching rates and a narrow measurement ...Particle tracking velocimetry(PTV)is one of the most commonly applied granular flow velocity measurement methods.However,traditional PTV methods may have issues such as high mismatching rates and a narrow measurement range when measuring granular flows with large bulk density and high-speed contrast.In this study,a novel PTV method is introduced to solve these problems using an optical flow matching algorithm with two further processing steps.The first step involves displacement correction,which is used to solve the mismatching problem in the case of high stacking density.The other step is trajectory splicing,which is used to solve the problem of a measurement range reduction in the case of high-speed contrast The hopper flow experimental results demonstrate superior performance of this proposed method in controlling the number of mismatched particles and better measuring efficiency in comparison with the traditional PTV method.展开更多
This paper describes the use of particle tracking velocimetry to analyze the Lagrangian acceleration of small particles in superfluid helium with varying time increments, . The probability density of acceleration exhi...This paper describes the use of particle tracking velocimetry to analyze the Lagrangian acceleration of small particles in superfluid helium with varying time increments, . The probability density of acceleration exhibits Gaussian properties for <sub></sub><sub></sub>, but displays a lognormal distribution for , where <sub></sub><sub></sub> is the migration time characterizing the particle motion. The particle trajectories are well characterized by the Hurst exponent H. For smaller time scales than <sub></sub><sub></sub>, the trajectories exhibit linear motion (), but have certain fractal properties with for time scales larger than <sub></sub>.展开更多
The experimental characterization of particle dynamics in fluidized beds is of great importance in fostering an understanding of solid phase motion and its effect on particle properties in granulation processes, Commo...The experimental characterization of particle dynamics in fluidized beds is of great importance in fostering an understanding of solid phase motion and its effect on particle properties in granulation processes, Commonly used techniques such as particle image velocimetry rely on the cross-correlation of illumination intensity and averaging procedures. It is not possible to obtain single particle velocities with such techniques. Moreover, the estimated velocities may not accurately represent the local particle velocities in regions with high velocity gradients. Consequently, there is a need for devices and methods that are capable of acquiring individual particle velocities. This paper describes how particle tracking velocimetry can be adapted to dense particulate flows. The approach presented in this paper couples high-speed imaging with an innovative segmentation algorithm for particle detection, and employs the Voronoi method to solve the assignment problem usually encountered in densely seeded fows. Lagrangian particle tracks are obtained as primary information, and these serve as the basis for calculating sophisticated quantities such as the solid-phase flow field, granular temperature, and solid volume fraction. We show that the consistency of individual trajectories is sufficient to recognize collision events.展开更多
An inverse analysis algorithm is proposed for estimating liquid phase flowfield from measurement data of bubble motion. This kind of technology will be applied in future forvarious estimation of fluid flow in rivers, ...An inverse analysis algorithm is proposed for estimating liquid phase flowfield from measurement data of bubble motion. This kind of technology will be applied in future forvarious estimation of fluid flow in rivers, lakes, sea surface flow, and also microscopic channelflow as the problem-handling in civil, mechanical, electronic, and chemical engineering. Therelationship between the dispersion motion and the carrier phase flow is governed and expressed bythe trans-lational motion equation of spherical dispersion. The equation consists of all the forcecomponents including inertia, added inertia, drag, lift, pressure gradient force and gravity force.Using this equation enables us to estimate the carrier phase flow structure using only the data ofthe dispersion motioa Whole field liquid flow structure is also estimated using spatial or temporalinterpolation method. In order to verify this principle, the Taylor-Green vortex flow, and theKarman vortex shedding from a square cylinder have been chosea The results show that the combinationof the inverse analysis and Particle Tracking Velocimetry (PTV) with the spatio-temporalpostprocessing algorithm could reconstruct well the carrier phase flow of the gas-liquid two-phaseflow.展开更多
Residence time distributions （RTDs） in horizontal fluidised beds have a huge effect on solid product properties and are infuenced by the internal design of the apparatus, e.g. the separation into different compartme...Residence time distributions （RTDs） in horizontal fluidised beds have a huge effect on solid product properties and are infuenced by the internal design of the apparatus, e.g. the separation into different compartments by weirs. Weirs can be passed in or against the overall solid transport direction, with the back-flow resulting in axial dispersion, which is a measure of the spread of the RTD. Therefore, the ratio of exchange rates at weirs under different fluidisation conditions provides information on axial dispersion. In this work, a methodology based on particle tracking velocimetry is presented to obtain information on the exchange rates of particles at weirs in horizontal fluidised beds. The internal recirculation is studied for over-flow weirs with respect to different fluidisation conditions, providing a first step towards determining the effects of weirs and fluidisation conditions on axial dispersion and RTDs in horizontal fluidised beds.展开更多
The tracking characteristics of tracer particles for particle image velocimetry（PIV） measurements in supersonic flows were investigated.The experimental tests were conducted at Mach number 4 in Multi-Mach Wind Tunne...The tracking characteristics of tracer particles for particle image velocimetry（PIV） measurements in supersonic flows were investigated.The experimental tests were conducted at Mach number 4 in Multi-Mach Wind Tunnel（MMWT） of Shanghai Jiao Tong University.The motion of tracer particles carried by the supersonic flow across Shockwaves was theoretically modelled,and then their aerodynamic characteristics with compressibility and rarefaction effects were evaluated.According to the proposed selection criterion of tracer particles,the PIV measured results clearly identified that the Shockwave amplitude is in good agreement with theory and Schlieren visualizations.For the tracer particles in nanoscales,their effective aerodynamic sizes in the diagnostic zone can be faithfully estimated to characterize the tracking capability and dispersity performance based on their relaxation motion across oblique Shockwaves.On the other hand,the seeding system enabled the tracer particles well-controlled and repeatable dispersity against the storage and humidity.展开更多
The Basset-Boussinesq-Oseen （BBO） equation can be used for most flows to trace the motion of a particle, but in a centrifugal pump, among the forces that act on the particles, one should also include those due to th...The Basset-Boussinesq-Oseen （BBO） equation can be used for most flows to trace the motion of a particle, but in a centrifugal pump, among the forces that act on the particles, one should also include those due to the impeller rotation, as additional effects. This paper firstly reviews various approximations of the BBO equation for the motion of dispersion particles in a viscous fluid. Then based on the motion equation for particles in low Reynolds number centrifugal pumps, a formula for calculating the tracking characteristics of tracer particles is deduced through the Fourier integral transformation. After that the deviations of the particle motion from the fluid motion, as predicted by the various approximations, are discussed and compared. At last, with an emphasis on the Particle Image Velocimetry （PIV） results, the tracking characteristics of particles are estimated. Also, advantages and disadvantages of different tracer particles are discussed and suitable tracer particles for application in PIV studies for flow fields in centrifugal pumps are suggested.展开更多
Particle tracking techniques such as magnetic particle tracking,radioactive particle tracking and positron emission particle tracking are widely used in academia and industry to image the dynamics of particulate and m...Particle tracking techniques such as magnetic particle tracking,radioactive particle tracking and positron emission particle tracking are widely used in academia and industry to image the dynamics of particulate and multiphase systems.These techniques can provide detailed data concerning a range of important,whole-field quantities based only on the time-averaged dynamics of a small number of tracer particles.However,in order for this data to be reliable,the duration over which these time-averages are taken must be suitably long.Further,the‘minimum averaging time’required to produce good statistics depends sensitively on the system in question and,at present,cannot be determined a priori in advance of an experiment.In this paper,we take a step toward resolving this issue,using discrete element method simulations of a simple vibrofluidised granular bed to develop a series of scaling laws relating said minimum averaging time to a variety of key system variables.The scaling laws developed may be used by future experimentalists to predict the required averaging time for each given system during an experimental campaign,thus improving both the efficiency with which particle tracking techniques may be applied,and the reliability of the data produced thereby.展开更多
We constructed a volume particle-tracking velocimetry (Volume-PTV) algorithm for comparisons with the tomographic particle image velocimetry (Tomo-PIV) algorithm, in which the multiplicative algebraic reconstruction t...We constructed a volume particle-tracking velocimetry (Volume-PTV) algorithm for comparisons with the tomographic particle image velocimetry (Tomo-PIV) algorithm, in which the multiplicative algebraic reconstruction technique (MART) was adopted. Performance tests on both algorithms were conducted by using artificial images generated through numerical data sets. Standard data on an impinging jet were used to test the Volume-PTV algorithm, whereas ring vortex data were used to test the Tomo-PIV algorithm. The influence of the number of particles (particle density in volume) on the key factors of Volume-PTV, such as particle movements and particle neighborhoods, were investigated. Furthermore, the effects of particle density and sizes onto the recovery ratio of the vectors were evaluated.展开更多
Volumetric particle image velocimetry(PIV)is a laser technique measuring three-component velocity field in a volume.Common volumetric PIV techniques are defocusing PIV,multi-view PIV and holographic PIV.Tomographic PI...Volumetric particle image velocimetry(PIV)is a laser technique measuring three-component velocity field in a volume.Common volumetric PIV techniques are defocusing PIV,multi-view PIV and holographic PIV.Tomographic PIV is an advanced approach of multi-view PIV,which significantly improves the spatial resolution of the measurement by using the multiplicative algebraic reconstruction technique(MART)to reconstruct the particle field.Due to the rapid progress being made in volumetric PIV measurements,this article focuses on introducing the principles of different volumetric PIV methods from aspects of particle reconstruction and velocity reconstruction.Advantages and limitations on applications are elaborated.Issues specific to volumetric PIV regarding illumination,digital imaging,depth of focus,ghost particle and spatial resolution are discussed.展开更多
文摘The present work introduces an extension to three-dimensional Particle Tracking Velocimetry (3-D PTV) in order to investigate small-scale flow patterns. Instead of using monochrome particles the novelty over the prior state of the art is the use of differently dyed tracer particles and the identification of particle color classes directly on Bayer raw images. Especially in the case of a three camera setup it will be shown that the number of ambiguities is dramatically decreased when searching for homologous points in different images. This refers particularly to the determination of spatial parti- cle positions and possibly to the linking of positions into trajectories. The approach allows the handling of tracer parti- cles in high numbers and is therefore perfectly suited for gas flow investigations. Although the idea is simple, difficult- ties may arise particularly in determining the color class of individual particle when its projection on a Bayer sensor is too small. Hence, it is not recommended to extract features from RGB images for color class recognition due to infor- mation loss during the Bayer demosaicing process. This article demonstrates how to classify the color of small sized tracers directly on Bayer raw images.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11572201 and 91634202)
文摘Particle tracking velocimetry(PTV)is one of the most commonly applied granular flow velocity measurement methods.However,traditional PTV methods may have issues such as high mismatching rates and a narrow measurement range when measuring granular flows with large bulk density and high-speed contrast.In this study,a novel PTV method is introduced to solve these problems using an optical flow matching algorithm with two further processing steps.The first step involves displacement correction,which is used to solve the mismatching problem in the case of high stacking density.The other step is trajectory splicing,which is used to solve the problem of a measurement range reduction in the case of high-speed contrast The hopper flow experimental results demonstrate superior performance of this proposed method in controlling the number of mismatched particles and better measuring efficiency in comparison with the traditional PTV method.
文摘This paper describes the use of particle tracking velocimetry to analyze the Lagrangian acceleration of small particles in superfluid helium with varying time increments, . The probability density of acceleration exhibits Gaussian properties for <sub></sub><sub></sub>, but displays a lognormal distribution for , where <sub></sub><sub></sub> is the migration time characterizing the particle motion. The particle trajectories are well characterized by the Hurst exponent H. For smaller time scales than <sub></sub><sub></sub>, the trajectories exhibit linear motion (), but have certain fractal properties with for time scales larger than <sub></sub>.
基金funding of this work by the German Federal Ministry of Science and Education(BMBF) as part of the InnoProfile-Transfer project NaWiTec(03IPT701X)
文摘The experimental characterization of particle dynamics in fluidized beds is of great importance in fostering an understanding of solid phase motion and its effect on particle properties in granulation processes, Commonly used techniques such as particle image velocimetry rely on the cross-correlation of illumination intensity and averaging procedures. It is not possible to obtain single particle velocities with such techniques. Moreover, the estimated velocities may not accurately represent the local particle velocities in regions with high velocity gradients. Consequently, there is a need for devices and methods that are capable of acquiring individual particle velocities. This paper describes how particle tracking velocimetry can be adapted to dense particulate flows. The approach presented in this paper couples high-speed imaging with an innovative segmentation algorithm for particle detection, and employs the Voronoi method to solve the assignment problem usually encountered in densely seeded fows. Lagrangian particle tracks are obtained as primary information, and these serve as the basis for calculating sophisticated quantities such as the solid-phase flow field, granular temperature, and solid volume fraction. We show that the consistency of individual trajectories is sufficient to recognize collision events.
文摘An inverse analysis algorithm is proposed for estimating liquid phase flowfield from measurement data of bubble motion. This kind of technology will be applied in future forvarious estimation of fluid flow in rivers, lakes, sea surface flow, and also microscopic channelflow as the problem-handling in civil, mechanical, electronic, and chemical engineering. Therelationship between the dispersion motion and the carrier phase flow is governed and expressed bythe trans-lational motion equation of spherical dispersion. The equation consists of all the forcecomponents including inertia, added inertia, drag, lift, pressure gradient force and gravity force.Using this equation enables us to estimate the carrier phase flow structure using only the data ofthe dispersion motioa Whole field liquid flow structure is also estimated using spatial or temporalinterpolation method. In order to verify this principle, the Taylor-Green vortex flow, and theKarman vortex shedding from a square cylinder have been chosea The results show that the combinationof the inverse analysis and Particle Tracking Velocimetry (PTV) with the spatio-temporalpostprocessing algorithm could reconstruct well the carrier phase flow of the gas-liquid two-phaseflow.
文摘Residence time distributions （RTDs） in horizontal fluidised beds have a huge effect on solid product properties and are infuenced by the internal design of the apparatus, e.g. the separation into different compartments by weirs. Weirs can be passed in or against the overall solid transport direction, with the back-flow resulting in axial dispersion, which is a measure of the spread of the RTD. Therefore, the ratio of exchange rates at weirs under different fluidisation conditions provides information on axial dispersion. In this work, a methodology based on particle tracking velocimetry is presented to obtain information on the exchange rates of particles at weirs in horizontal fluidised beds. The internal recirculation is studied for over-flow weirs with respect to different fluidisation conditions, providing a first step towards determining the effects of weirs and fluidisation conditions on axial dispersion and RTDs in horizontal fluidised beds.
基金supported by the National Natural Science Foundation of China(Nos.11672183,91641129 and 91441205)
文摘The tracking characteristics of tracer particles for particle image velocimetry（PIV） measurements in supersonic flows were investigated.The experimental tests were conducted at Mach number 4 in Multi-Mach Wind Tunnel（MMWT） of Shanghai Jiao Tong University.The motion of tracer particles carried by the supersonic flow across Shockwaves was theoretically modelled,and then their aerodynamic characteristics with compressibility and rarefaction effects were evaluated.According to the proposed selection criterion of tracer particles,the PIV measured results clearly identified that the Shockwave amplitude is in good agreement with theory and Schlieren visualizations.For the tracer particles in nanoscales,their effective aerodynamic sizes in the diagnostic zone can be faithfully estimated to characterize the tracking capability and dispersity performance based on their relaxation motion across oblique Shockwaves.On the other hand,the seeding system enabled the tracer particles well-controlled and repeatable dispersity against the storage and humidity.
基金supported by the National Outstanding Young Scientist Funds of China (Grant No.50825902)the Jiangsu Provincial Innovative Scholars "Climbing" Project of China(Grant No.BK2009006)the National Natural Science Foundation of China (Grant No.50979034)
文摘The Basset-Boussinesq-Oseen （BBO） equation can be used for most flows to trace the motion of a particle, but in a centrifugal pump, among the forces that act on the particles, one should also include those due to the impeller rotation, as additional effects. This paper firstly reviews various approximations of the BBO equation for the motion of dispersion particles in a viscous fluid. Then based on the motion equation for particles in low Reynolds number centrifugal pumps, a formula for calculating the tracking characteristics of tracer particles is deduced through the Fourier integral transformation. After that the deviations of the particle motion from the fluid motion, as predicted by the various approximations, are discussed and compared. At last, with an emphasis on the Particle Image Velocimetry （PIV） results, the tracking characteristics of particles are estimated. Also, advantages and disadvantages of different tracer particles are discussed and suitable tracer particles for application in PIV studies for flow fields in centrifugal pumps are suggested.
文摘Particle tracking techniques such as magnetic particle tracking,radioactive particle tracking and positron emission particle tracking are widely used in academia and industry to image the dynamics of particulate and multiphase systems.These techniques can provide detailed data concerning a range of important,whole-field quantities based only on the time-averaged dynamics of a small number of tracer particles.However,in order for this data to be reliable,the duration over which these time-averages are taken must be suitably long.Further,the‘minimum averaging time’required to produce good statistics depends sensitively on the system in question and,at present,cannot be determined a priori in advance of an experiment.In this paper,we take a step toward resolving this issue,using discrete element method simulations of a simple vibrofluidised granular bed to develop a series of scaling laws relating said minimum averaging time to a variety of key system variables.The scaling laws developed may be used by future experimentalists to predict the required averaging time for each given system during an experimental campaign,thus improving both the efficiency with which particle tracking techniques may be applied,and the reliability of the data produced thereby.
文摘We constructed a volume particle-tracking velocimetry (Volume-PTV) algorithm for comparisons with the tomographic particle image velocimetry (Tomo-PIV) algorithm, in which the multiplicative algebraic reconstruction technique (MART) was adopted. Performance tests on both algorithms were conducted by using artificial images generated through numerical data sets. Standard data on an impinging jet were used to test the Volume-PTV algorithm, whereas ring vortex data were used to test the Tomo-PIV algorithm. The influence of the number of particles (particle density in volume) on the key factors of Volume-PTV, such as particle movements and particle neighborhoods, were investigated. Furthermore, the effects of particle density and sizes onto the recovery ratio of the vectors were evaluated.
基金supported by the National Natural Science Foundation of China(11102013 and 11327202)the"Weishi"Foundation of Beijing University of Aeronautics and Astronautics(YWF-12-RHRS-008)
文摘Volumetric particle image velocimetry(PIV)is a laser technique measuring three-component velocity field in a volume.Common volumetric PIV techniques are defocusing PIV,multi-view PIV and holographic PIV.Tomographic PIV is an advanced approach of multi-view PIV,which significantly improves the spatial resolution of the measurement by using the multiplicative algebraic reconstruction technique(MART)to reconstruct the particle field.Due to the rapid progress being made in volumetric PIV measurements,this article focuses on introducing the principles of different volumetric PIV methods from aspects of particle reconstruction and velocity reconstruction.Advantages and limitations on applications are elaborated.Issues specific to volumetric PIV regarding illumination,digital imaging,depth of focus,ghost particle and spatial resolution are discussed.
