A novel approach to digital particle tracking velocimetry (DPTV) based on cross-correlation digital particle image velocimetry (DPIV) is presented that eliminates the need to interpolate the randomly located velocity vectors (typical of tracking techniques) and results in significantly improved resolution and accuracy. In particular, this approach allows for the direct measurement of mean squared fluctuating gradients, and thus several important components of the turbulent dissipation. The effect of various parameters (seeding density, particle diameter, dynamic range, out-of-plane motion, and gradient strength) on accuracy for both DPTV and DPIV are investigated using a Monte Carlo simulation and optimal values are reported. Validation results are presented from the comparison of measurements by the DPTV technique in a turbulent flat plate boundary layer to laser Doppler anemometer (LDA) measurements in the same flow as well as direct numerical simulation (DNS) data. The DPIV analysis of the images used for the DPTV validation is included for comparison.

A hybrid digital particle tracking velocimetry technique

A high-speed video system was used to study the interaction between sediment particles and turbulence in the wall region of an open channel flow with both smooth and transitionally rough beds. In smooth flows, particles immersed within the viscous sublayer were seen to accumulate along low-speed wall streaks; apparently due to the presence of quasi-streamwise vortices in the wall region. Larger particles did not tend to group along streaks, however their velocity was observed to respond to the streaky structure of the flow velocity in the wall region. In transitionally rough flows particle sorting was not observed. Coherent flow structures in the form of shear layers typically observed in the near-wall region interacted with sediment particles lying on the channel bottom, resulting in the particles being entrained into suspension. Although there has been some speculation that this process would not be effective in entraining particles totally immersed in the viscous sublayer, the results obtained demonstrate the opposite. The entrainment mechanism appears to be the same independent of the roughness condition of the bottom wall, smooth or transitionally rough. In the latter case, however, hiding effects tend to preclude the entrainment of particles with sizes finer than that of the roughness elements. The analysis of particle velocity during entrainment shows that the streamwise component tends to be much smaller than the local mean flow velocity, while the vertical component tends to be much larger than the local standard deviation of the vertical flow velocity fluctuations, which would indicate that such particles are responding to rather extreme flow ejection events.

Experiments on particle—turbulence interactions in the near–wall region of an open channel flow: implications for sediment transport

A condensed review of recent advances accomplished in the development and the applications of noninvasive tomographic and velocimetric measurement techniques to multiphase flows and systems is presented. In recent years utilization of such noninvasive techniques has become widespread in many engineering disciplines that deal with systems involving two immiscible phases or more. Tomography provides concentration, holdup, or 2D or 3D density distribution of at least one component of the multiphase system, whereas velocimetry provides the dynamic features of the phase of interest such as the flow pattern, the velocity field, the 2D or 3D instantaneous movements, etc. The following review is divided into two parts. The first part summarizes progress and developments in flow imaging techniques using γ-ray and X-ray transmission tomography; X-ray radiography; neutron transmission tomography and radiography; positron emission tomography; X-ray diffraction tomography; nuclear magnetic resonance imaging; electrica...

Noninvasive Tomographic and Velocimetric Monitoring of Multiphase Flows

Optical measurement techniques such as particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) are now routinely used in experimental fluid mechanics to investigate pure fluids or dilute suspensions. For highly concentrated particle suspensions, material turbidity has long been a substantial impediment to these techniques, which explains why they have been scarcely used so far. A renewed interest has emerged with the development of specific methods combining the use of iso-index suspensions and imaging techniques. This review paper gives a broad overview of recent advances in visualization techniques suited to concentrated particle suspensions. In particular, we show how classic methods such as PIV, LDV, particle tracking velocimetry, and laser induced fluorescence can be adapted to deal with concentrated particle suspensions.

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Refractive-index and density matching in concentrated particle suspensions: a review

A three-dimensional Particle Tracking Velocimetry (3-D PTV) technique has been developed to provide time-resolved, three-dimensional velocity field measurements throughout a finite volume. This technique offers many advantages for fundamental research in turbulence and applied research in areas such as mixing and combustion. The data acquired in 3-D PTV is a time sequence of stereo images of flow tracer particles suspended in the fluid. In this paper, the implementation of the technique is discussed in detail, as well as the results of an extensive statistical investigation of the performance of the algorithms. The technique has been optimized to allow fully automatic processing of long sequences of image pairs in a computationally efficient manner, hereby providing a viable, practical tool for the study of complex flows.

Algorithms for fully automated three-dimensional particle tracking velocimetry

Simultaneous velocity measurements of both components of a two-phase flow using particle image velocimetry

The practical use of particle image velocimetry (PIV) requires the use of fast, reliable, computer-based methods for tracking numerous particles suspended in a fluid flow. Two methods for performing tracking are presented. One method tracks a particle through multiple, sequential images (minimum of four required) by prediction and verification of particle displacement and direction. The other method, requiring only two sequential images, uses a dynamic, binary, spatial, cross-correlation technique. The algorithms were tested on both synthetic data and experimental data which were obtained with traditional PIV methods. This allowed error analysis and testing of the algorithms on real engineering flows.

http://iopscience.iop.org/article/10.1088/0957-0233/3/7/001/pdf

PIV flow visualisation using particle tracking techniques

Digital pulsed laser velocimetry (DPLV)is a novel full-field, twodimensional, noninvasive, quantitative flow visualization technique. A description of the technique, which uses direct digitization of single- or twophase flow images using a high-resolution imaging system and a highpower pulsed laser, is presented. Images (ten consecutive frames of data separated by a time increment of 150 ms) of single- and two-phase flow over a step are acquired with a high-resolution camera. Each of these ten frames contains the images of tracer articles or bubbles at that one instant of time. The image data was stored for further analysis by new image processing and analysis software developed specifically for flow experiments. An image finding, smoothing, and defining program was developed. This program groups appropriate pixels into particles, smooths the image, and calculates important parameters for the image. Another program was developed to match the particles from each of the frames into tracks through time. The program uses a statistical technique to determine the best possible path of the particles. The most important capability of pulsed laser velocimetry is the ability to use these image processing techniques to capture simultaneous and quantitative rather than qualitative information.

Flow velocity measurements using digital pulsed laser velocimetry

Digital Pulsed Laser Velocimetry (DPLV) is a full-field, two dimensional, noninvasive, quantitative flow visualization technique. The technique described here includes the novel use of direct digitization of two-phase bubbly flow images using a high resolution imaging system. The image data is stored for further analysis by new image processing and analysis software developed for flow experiments. In the technique, ten consecutive frames of data separated by a time increment of 150 ms, are recorded. Each of these ten frames contains the images of bubbles at that one instant of time. A program smooths the instantaneous image and calculates bubble parameters. Another program matches the bubbles from each of the frames into tracks of bubbles through time. This program uses a statistical technique to determine the best possible path of the bubbles. The ability of pulsed laser velocimetry to capture simultaneous and quantitative rather than qualitative information along with these image processing techniques gives the experimentalist a powerful tool to perform flow visualization and analysis.

Full-field bubbly flow velocity measurements by digital image pulsed laser velocimetry

Digital Pulsed Laser Velocimetry (DPLV) is a novel full-field, two dimensional, noninvasive, quantitative flow
visualization technique. The technique described here includes the use of direct digitization of the images for flow
analysis using a high resolution imaging system. The image data is stored for further analysis by a series of new image
processing and analysis software developed for flow experiments.
The imaging processing and analysis software developed includes a compression program for reducing storage
requirements of the image data to 10%. An image finding, smoothing, and defining program has also been developed.
Analysis time has been greatly reduced and the software is now running on a PC/AT compatible. This program groups
pixels that could logically be defined as one image, smooths that image and calculates important parameters for the
image.
In the technique images via a high resolution camera (1024 x 1024), ten consecutive frames of data, separated by a
time increment of 150 ms, are recorded. Each of these ten frames contains the images of particles at that one instant of
time. A third computer program is developed to match the image from each of the frames into tracks of the particles
through time. The program uses a statistical technique to determine the best possible path of the fluid seeds.
The ability of pulsed laser velocimetry with these image processing techniques to capture simultaneous and
quantitative rather than qualitative information is its most important capability.

Thomas K . Blanchat

Papers

Simultaneous velocity measurements of both components of a two-phase flow using particle image velocimetry

PIV flow visualisation using particle tracking techniques

Flow velocity measurements using digital pulsed laser velocimetry

Full-field bubbly flow velocity measurements by digital image pulsed laser velocimetry

Full-field velocity imaging technique using high-energy pulsed laser velocimetry