Tracer Particles In Flow Research Articles

A 3-D Printed Optically Clear Rigid Diseased Carotid Bifurcation Arterial Mock Vessel Model for Particle Image Velocimetry Analysis in Pulsatile Flow

Abstract In recent years, blood flow analyses of diseased arterial mock vessels using particle image velocimetry (PIV) have been hampered by the inability to fabricate optically clear anatomical vessel models that realistically replicate the complex morphology of arterial vessels and provide highly resolved flow images of flow tracer particles. The aim of this paper is to introduce a novel approach for producing optically clear 3-D printed rigid anatomical arterial vessel models that are suitable for PIV analysis using a common 3-D inkjet printing process (using a Formlabs Form 2 3-D printer) and stock clear resin (RS-F2-GPCL-04). By matching the index of refraction (IOR) of the working fluid to the stock clear resin material, and by printing the part in a 45-deg print orientation, a clear anatomical model that allows clear visualization of flow tracer particles can be produced which yields highly resolved flow images for PIV analyses. However, a 45-deg print orientation increases the need for post-processing due to an increased amount of printed support material. During post-processing, the part must be wet sanded in several steps and surface finished with Novus Plastic Polish 3 Step System to achieve the final surface finish needed to yield high-resolution flow images. The mock arterial vessel model produced in this work is a 3-D printed diseased carotid bifurcation artery developed from CTA scan data. A PIV analysis was conducted on the developed mock arterial vessel model installed in a complex transient flow loop to assess the flow profiles within the model and the clarity of the model. A computational fluid dynamics (CFD) simulation was conducted on the same carotid bifurcation arterial geometry, and the results were used as a benchmark comparison for PIV results. The results obtained in this work show excellent promise for using the developed approach for developing 3-D printed anatomical vessel models for experimental PIV analyses. The fabrication methodology of the clear anatomical models, PIV results, and CFD results is described in detail.

Effect of surface roughness on heat transfer in Rayleigh-Bénard convection

This paper reports on an experimental study of the effects of surface roughness on the flow and heat transfer in cubical Rayleigh-Bénard convection cells for Rayleigh numbers between 107 and 1010. In the rough cells the top and bottom surfaces are equipped with square arrays of copper cubes. In line with other studies, three different regimes occur in the rough cells, with each regime having a different relation between the Nusselt number, Nu, and the Rayleigh number, Ra. In the first regime the Nu-Ra relation equals that of the smooth cell, but in the second and third regimes the Nu-Ra relation deviates from that of the smooth cell with significantly higher Nusselt numbers. To better understand these observations, the flow and temperature fields in both the smooth and rough cells were visualised by using particle image velocimetry with suspended thermochromic liquid crystals as flow tracer particles.

Correction of PIV data for reconstruction of the gas velocity in a supersonic underexpanded jet

A method of correction of particle image velocimetry (PIV) data for reconstruction of the gas velocity based on the particle velocity in supersonic underexpanded jets is considered. The method is based on estimating the velocity lag of tracer particles on the basis of their velocity relaxation parameter as a correction to PIV data in the Newton approximation of interphase interaction. It is shown that the velocity relaxation parameter of tracer particles in flows with velocity jumps can be determined from the initial PIV data. Correction with the found parameter of velocity relaxation of the phases provides good accuracy.

PIV Measurement of Velocity Distribution in the Moderator Circulation Test (MCT)

Korea Atomic Energy Research Institute (KAERI) has been carrying out a scaled-down moderator test program to simulate the CANDU-6 moderator circulation phenomena during steady state operation and accident conditions. The Moderator Circulation Test (MCT) facility was designed and constructed as 1/4 scale of the prototype of CANDU-6 reactor. In the present work spatial distribution of two-dimensional velocity in the MCT facility under isothermal condition was measured using planar Particle Image Velocimetry (PIV) system which consists of double pulsed laser, synchronizer, and high speed camera. TSI’s Insight TM 4G software was used to perform PIV image capturing, PIV calculation and post processing. 10 μm sized silver-coated hollow sphere particles were used as flow tracer particles. Multiple experiments were conducted to cover large area of the MCT facility with limited field of view of a single camera. Instantaneous and averaged velocity field were analyzed for each spatial position and flow rate. This research is capable of offering validation data for self-reliant CFD tools to predict moderator subcooling margin in CANDU-6 reactor.

An Optimized Method for Delivering Flow Tracer Particles to Intravital Fluid Environments in the Developing Zebrafish

Growing evidence suggests that intravital flow-structure interactions are critical morphogens for normal embryonic development and disease progression, but fluid mechanical studies aimed at investigating these interactions have been limited in their ability to visualize and quantify fluid flow. In this study, we describe a protocol for injecting small (≤1.0 μm) tracer particles into fluid beds of the larval zebrafish to facilitate microscale fluid mechanical analyses. The microinjection apparatus and associated borosilicate pipette design, typically blunt-tipped with a 2-4 micron tip O.D., yielded highly linear (r(2)=0.99) in vitro bolus ejection volumes. The physical characteristics of the tracer particles were optimized for efficient particle delivery. Seeding densities suitable for quantitative blood flow mapping (≥50 thousand tracers per fish) were routinely achieved and had no adverse effects on zebrafish physiology or long-term survivorship. The data and methods reported here will prove valuable for a broad range of in vivo imaging technologies [e.g., particle-tracking velocimetry, μ-Doppler, digital particle image velocimetry (DPIV), and 4-dimensional-DPIV] which rely on tracer particles to visualize and quantify fluid flow in the developing zebrafish.

3D Flow reconstruction using ultrasound PIV

Ultrasound particle image velocimetry (PIV) can be used to obtain velocity fields in non-transparent geometries and/or fluids. In the current study, we use this technique to document the flow in a curved tube, using ultrasound contrast bubbles as flow tracer particles. The performance of the technique is first tested in a straight tube, with both steady laminar and pulsatile flows. Both experiments confirm that the technique is capable of reliable measurements. A number of adaptations are introduced that improve the accuracy and applicability of ultrasound PIV. Firstly, due to the method of ultrasound image acquisition, a correction is required for the estimation of velocities from tracer displacements. This correction accounts for the fact that columns in the image are recorded at slightly different instances. The second improvement uses a slice-by-slice scanning approach to obtain three-dimensional velocity data. This approach is here demonstrated in a strongly curved tube. The resulting flow profiles and wall shear stress distribution shows a distinct asymmetry. To meaningfully interpret these three-dimensional results, knowledge of the measurement thickness is required. Our third contribution is a method to determine this quantity, using the correlation peak heights. The latter method can also provide the third (out-of-plane) component if the measurement thickness is known, so that all three velocity components are available using a single probe.

Three Dimensional Measurement of Particle Movement Using Rotating Beam Splitter and Coupled Mirror

The automatic inference of depth/distance information is a primary aim of computer vision systems. Though the stereovision method is often used for computer vision, finding matching pairs between frames can often be problematic, particularly when there are several possible choices of matching points. To address these problems, we have developed a depth measurement system that uses a single CCD camera. By setting the optical device in front of the camera lens, the image of a target recorded on the image plane is displaced by an amount related to the distance between the camera and the target. When the optical device is rotated physically at high speed during the exposure of the camera, the image of a moving target traces a spiral streak. Since the size of the streak is inversely proportional to the depth and the pitch and size variation of the spiral relates to the velocity of the moving target, the 3-D information of the target can be obtained by analyzing the streak. In order to make image processing easier, the spiral streaks and their corresponding center line are recorded on the same image. The center line helps in analyzing the streaks. This method has been applied to the measurement of moving tracer particles in flow and satisfactory results were obtained.

3D scanning particle tracking velocimetry

In this article, we present an experimental setup and data processing schemes for 3D scanning particle tracking velocimetry (SPTV), which expands on the classical 3D particle tracking velocimetry (PTV) through changes in the illumination, image acquisition and analysis. 3D PTV is a flexible flow measurement technique based on the processing of stereoscopic images of flow tracer particles. The technique allows obtaining Lagrangian flow information directly from measured 3D trajectories of individual particles. While for a classical PTV the entire region of interest is simultaneously illuminated and recorded, in SPTV the flow field is recorded by sequential tomographic high-speed imaging of the region of interest. The advantage of the presented method is a considerable increase in maximum feasible seeding density. Results are shown for an experiment in homogenous turbulence and compared with PTV. SPTV yielded an average 3,500 tracked particles per time step, which implies a significant enhancement of the spatial resolution for Lagrangian flow measurements.

Experimental Measurements of the Spatial Distribution of 3-D Lagrangian Dispersion Rates.

The mixing phenomenon in fluid flow fields has two major components : the advective mixing process driven by the large scale fluid motions and the diffusive mixing process driven by small scale molecular interactions. It is well accepted and amply demonstrated that, in many flows of interest to engineering the overall mixing can be strongly enhanced by an efficient advective mixing, i.e.by bringing the different species involved in close proximity to each other for molecular diffusion to take place over a short period of time. Over the past several years, we have developed an experimental 3-D fluid measurement technique, namely 3-D particle tracking velocimetry(PTV), in which the 3-D fluid velocities are determined by establishing(by photographic means)the 3-D trajectories of flow tracer particles. This paper describes a method for extracting 3-D Lagrangian dispersion rates from such 3-D PTV measurements. Specifically, a quantitative measure of the advective mixing is obtained by evaluating the normal dispersion rate of instantaneous nearby physical trajectories(in direction normal to the instantaneous local velocity vector). Then the magnitude of the root mean square(rms)of the instantaneous local dispersion rate is computed(in the ensemble averaged sense)over many realizations throughout the entire volume of the fluid being studied. This technique is applied to an in-cylinder flow field in an internal combustion(IC)engine in order to promote a better under-standing of mixing characteristics by comparing the spatial distribution of the normal dispersion to the 3-D flow patterns.

Velocity fidelity of flow tracer particles

Recent developments concerning the unsteady dynamic forces on a spherical particle at finite Reynolds number are reviewed for solid particles and clean micro-bubble. A particle frequency :response function and an energy transfer function are derived for a solid particle or a contaminated micro-bubble in gas or liquid flow. A simple, unified method for estimating the cut-off frequency, or cut-off size, of a solid particle or a contaminated bubble is developed. Particle motion in isotropic turbulence is examined. Responses of the tracer particle to integral length scale structure, to turbulence energy, and to Taylor micro-scale structure are discussed in terms of the particle turbulence diffusivity, the particle turbulence intensity, and the ensemble average of the second invariant of fluid turbulence deformation tensor evaluated on the particle trajectory.

Algorithms for fully automated three-dimensional particle tracking velocimetry

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.

Hydrodynamic dispersion and pore geometry in consolidated rock

Experimental measurements of the dispersion of tracer particles in flow through natural porous media are compared with a percolation model. The experiments show that tracer dispersion is a sensitive function of the width of the pore-size distribution as measured by mercury capillary pressure. Measurements of capillary pressure (or electrical conductivity) are used to estimate the geometric correlation length of the dominant flow path in the rock. Percolation theory is used to derive a power-law relationship between the correlation length and the ratio of the dispersivity to the average grain size. The experimental value of the power-law exponent is in agreement with the theoretical prediction. Measurements on samples containing a residual saturation of wetting epoxy show no significant change in dispersion behavior. This result mediates against dispersion models requiring trapping in dead-end pores. Tracer concentration profiles exhibit anomalous long-time tails in two cases. In carbonate rocks, we associate long-time tails with macroscopic permeability heterogeneities. In sandstones, long-time tails occur in samples with a very narrow pore-size distribution. These samples may have permeability heterogeneities as a result of defects in the packing density. In the limit of low flow velocity, the long-time tail disappears, suggesting a convective mechanism associated with flow heterogeneities at a millimeter-or-larger scale.

トレーサー粒子群運動の安定性

The motion of tracer particles in liquid flow is disscussed by the stability theorem of the macroscopic concept.When the volume fraction of the tracer particles in liquid flow is small, the neutral or stable stability condition can be expected in the motion of tracer particles in flow.

Stereo photography of neutral density He-filled bubbles for 3-D fluid motion studies in an engine cylinder

A new technique has been developed for studies of fluid motion within the cylinder of a reciprocating piston engine during the air induction process. Helium-filled bubbles, serving as neutrally buoyant flow tracer particles, enter the cylinder along with the inducted air charge. The bubble motion is recorded by stereo cine photography through the transparent cylinder of a specially designed research engine. Quantitative data on the 3-D velocity field generated during induction is obtained from frame-to-frame analysis of the stereo images, taking into account refraction of the rays due to the transparent cylinder. Other applications for which this technique appears suitable include measurements of velocity fields within intake ports and flow-field dynamics within intake manifolds of multicylinder engines.