Particle Tracking Velocimetry Experiments Research Articles

Optical Considerations for Designing Laser-Based Volumetric Particle Tracking Velocimetry

Abstract The trend to conduct volumetric Particle Tracking Velocimetry experiments with ever increasing volumes, at a given particle density, poses increasing challenges on the design of such experiments in terms of the power of the laser source and the image analysis. This, on one hand, requires a reliable model to estimate the signal level that is measured on a CMOS detector from a Mie scattering particle. On the other hand, it requires also a model for estimating the limiting factors upon the image resolution, where a large amount of particles within a 3D volume are mapped into a 2D image. Herein, we present a model that provides an analytical expression to estimate the signal level on a CMOS detector from a Mie scattering particle within an arbitrary large volume in a volumetric Particle Tracking Velocimetry experiment. We begin with a model for planar experiments and extend it into volumetric measurements. Our model considers the effect of the depth of field, particle density, Mie scattering signal and total Mie scattering loss, laser pulse-energy and relevant optical parameters. Later, we investigate the consequence of the Rayleigh criterion upon image resolution when it is applied to particles within a volume of interest. Finally, we demonstrate how we applied our model to estimate the signal level and the limit upon the spatial resolution in three experiments carried-out in our lab.

Meshless track assimilation (MTA) of 3D PTV data

We propose a data assimilation algorithm to improve the resolution of 3D particle tracking velocimetry (PTV) data and, as a byproduct, it estimates the pressure field. The proposed method, called meshless tracking assimilation (MTA), does not rely on a mesh to compute derivatives. Instead, it exploits the analytical formulation of the obtained field to extract the gradients of the involved quantities in arbitrary points. MTA actively constraints PTV data points to satisfy the Navier–Stokes equations in both time and space at user-defined spatial locations. Three test cases are investigated. The first one is a synthetic dataset reconstructed from a direct numerical simulation and it serves to ensure that the method is properly implemented and working. The second one is the 2020 data assimilation challenge which gives a qualitative comparison with other data assimilation methods. Finally, MTA is used on a Tomographic PTV experiment of a Jet Flow with ReD≃3000 to ensure it can be implemented successfully on experimental data. The first and third test cases show a significant performance boost compared to the classic linear interpolation. This improvement allows for a higher level of structural resolution without sacrificing the temporal and spatial smoothness of the solution. The second test case generally aligns well with other state-of-the-art data assimilation techniques in terms of performance, but there are some noticeable differences.

Assessment of the Nonlinear Electrophoretic Migration of Nanoparticles and Bacteriophages.

Bacteriophage therapy presents a promising avenue for combating antibiotic-resistant bacterial infections. Yet, challenges exist, particularly, the lack of a straightforward purification pipeline suitable for widespread application to many phage types, as some phages are known to undergo significant titer loss when purified via current techniques. Electrokinetic methods offer a potential solution to this hurdle, with nonlinear electrophoresis emerging as a particularly appealing approach due to its ability to discern both the size and shape of the target phage particles. Presented herein is the electrokinetic characterization of the mobility of nonlinear electrophoresis for two phages (SPN3US and ϕKZ) and three types of polystyrene nanoparticles. The latter served as controls and were selected based on their sizes and surface charge magnitude. Particle tracking velocimetry experiments were conducted to characterize the mobility of all five particles included in this study. The results indicated that the selected nanoparticles effectively replicate the migration behavior of the two phages under electric fields. Further, it was found that there is a significant difference in the nonlinear electrophoretic response of phages and that of host cells, as first characterized in a previous report, illustrating that electrokinetic-based separations are feasible. The findings from this work are the first characterization of the behavior of phages under nonlinear electrophoresis effects and illustrate the potential for the development of electrokinetic-based phage purification techniques that could aid the advancement of bacteriophage therapy.

On local isotropy and scale dependence of pair dispersion in turbulent canopy flows

Canopy flows in the atmospheric surface layer play important economic and ecological roles, governing the dispersion of passive scalars in the environment. The interaction of high-velocity fluid and large-scale surface-mounted obstacles in canopy flows produces drag and causes intense, inhomogeneous and anisotropic turbulence. In this work, we focus on the turbulent dispersion of passive scalars by studying the ‘pair dispersion’ – a statistical measure of relative motion between particles. We analyse the results of a three-dimensional particle tracking velocimetry experiment in a wind-tunnel canopy flow, focusing on small scales. We confirm the existence of local isotropy of pair dispersion at scales smaller than a characteristic shear length scale $L_\varGamma =(\epsilon /\varGamma ^3)^{1/2}$ , where $\epsilon$ and $\varGamma$ are the mean dissipation rate and shear rate, respectively. Furthermore, we show that pair dispersion in this locally isotropic regime is a scale-dependent super-diffusive process, similar to what occurs in homogeneous isotropic turbulent flows. In addition, we measure the pair relative velocity correlation function, showing that its de-correlation occurs in the locally isotropic regime, and discuss the implications of this observation for modelling pair dispersion. Thus, our study extends the fundamental understanding of turbulent pair dispersion to the anisotropic inhomogeneous turbulent canopy flow, bringing valuable information for modelling scalar dispersion in the atmospheric surface layer.

Biallelic DAW1 variants cause a motile ciliopathy characterized by laterality defects and subtle ciliary beating abnormalities

PurposeThe clinical spectrum of motile ciliopathies includes laterality defects, hydrocephalus, and infertility as well as primary ciliary dyskinesia when impaired mucociliary clearance results in otosinopulmonary disease. Importantly, approximately 30% of patients with primary ciliary dyskinesia lack a genetic diagnosis. MethodsClinical, genomic, biochemical, and functional studies were performed alongside in vivo modeling of DAW1 variants. ResultsIn this study, we identified biallelic DAW1 variants associated with laterality defects and respiratory symptoms compatible with motile cilia dysfunction. In early mouse embryos, we showed that Daw1 expression is limited to distal, motile ciliated cells of the node, consistent with a role in left-right patterning. daw1 mutant zebrafish exhibited reduced cilia motility and left-right patterning defects, including cardiac looping abnormalities. Importantly, these defects were rescued by wild-type, but not mutant daw1, gene expression. In addition, pathogenic DAW1 missense variants displayed reduced protein stability, whereas DAW1 loss-of-function was associated with distal type 2 outer dynein arm assembly defects involving axonemal respiratory cilia proteins, explaining the reduced cilia-induced fluid flow in particle tracking velocimetry experiments. ConclusionOur data define biallelic DAW1 variants as a cause of human motile ciliopathy and determine that the disease mechanism involves motile cilia dysfunction, explaining the ciliary beating defects observed in affected individuals.

Wake characteristics of complex-shaped snow particles: Comparison of numerical simulations with fixed snowflakes to time-resolved particle tracking velocimetry experiments with free-falling analogs

Experimental and numerical approaches have their own advantages and limitations, in particular, when dealing with complex phenomena such as snow particles falling at moderate Reynolds numbers (Re). Time-resolved, three-dimensional particle tracking velocimetry (4D-PTV) experiments of free-falling, three-dimensional (3D)-printed snowflakes' analogs shed light on the elaborate falling dynamics of irregular snow particles but present a lower resolution (tracer seeding density) and a limited field of view (domain size) to fully capture the wake flow. Delayed-detached eddy simulations of fixed snow particles do not realistically represent all the physics of a falling ice particle, especially for cases with unsteady falling attitudes, but accurately predict the drag coefficient and capture the wake characteristics for steadily falling snowflakes. In this work, we compare both approaches on time- and space-averaged flow quantities in the snowflake wake. First, we cross validate the two approaches for low Re cases, where close agreement of the wake features is expected, and second, we assess how strongly the unsteady falling motion perturbs the average wake pattern as compared to a fixed particle at higher Re. For steadily falling snowflakes, the fixed-particle model can properly represent the wake flow with errors within the experimental uncertainty (±15%). At moderate/high Re (unsteady falling motion), larger differences are present. Applying a co-moving frame to the experimental data to account for the particle movement or filtering the numerical data on larger grids reduces these differences only to some extent, implying that an unsteady fall significantly alters the average wake structure as compared to a fixed particle model.

A scaling relationship between power and shear for Bernoulli pads at equilibrium

Bernoulli pads can create a significant normal force on an object without contact. The radial outflow which creates this force also imposes a significant shear force on the object. Better understanding this shear force can improve pad designs in order to mitigate material deformation and damage, or allow the pads to be used as shear-based cleaning implements. Here, we use computational fluid dynamics to explore the parameter space and show a power-law relationship between the fluid power at the pad inlet and the maximum shear stress. These simulations are validated by a particle tracking velocimetry experiment. A relationship between the maximum shear stress and the inlet Reynolds number is provided, and some implications of the observed scaling relationships are explored.

Flow dynamics of droplets expelled during sneezing.

Respiratory infections transmit through droplets and aerosols generated by the infected individual during respiratory emissions. It is essential to study the flow dynamics of these emissions to develop strategies for mitigating the risk of infection. In particular, the dynamics of droplets expelled during violent exhalations such as sneezing is crucial, but has received little attention to date. Here, for the first time, we present the results of droplet dynamics of 35 sneezes, obtained from four volunteers, using particle tracking velocimetry experiments. Our results reveal a mean droplet velocity of 2–5.4 m/s across the different subjects. These values are significantly lower than what is usually assumed in the studies simulating or replicating sneezes. Furthermore, the large variation in droplet speeds, flow direction, spread angle, and head movement is also quantified. These findings will enable the refinement of models and simulations of sneezes toward improving infection control guidelines.

Research on noise processing and particle recognition algorithm of PTV image

Particle recognition and particle matching are the core of particle tracking velocimetry (PTV). Particle recognition and matching directly determine the accuracy of flow field analysis, and particle recognition is a prerequisite for matching. In the engineering application of PTV technology, there are various reasons for the image noise generated by shooting, which seriously interferes with particle recognition. Accurately separating particles from noise is the most important and difficult process in particle recognition while ensuring that particle information is not damaged. According to the particle image captured by PTV experiment, the author has proposed a new processing method for denoising and recognition of noise-containing original image (ImageDenoising-ParticleRecognition). This method comprehensively uses SUSAN detection, expansion calculation, threshold segmentation, four-connected mark, non-particle culling, particle hole filling and other technologies to protect the image information of particles from loss to the maximum extent and ensure that the noise-containing particle images can complete particle recognition in one step. At the same time, the method proposed in this paper more accurately determines the edge of the particle image, and provides a more reliable particle image for the calculation of the flow field motion in the later stage. For the method proposed in this paper, based on the Visual C++ platform autonomous programming, the particle images generated by computer simulation and the SiO2 particle image with 500 nm diameter shot by the actual PTV experiment have been verified and analyzed respectively, and the recognition results with good accuracy have been obtained. The preprocessing of particle image is the prerequisite of PTV processing, and its level directly has a crucial impact on the final analysis accuracy of the flow field. According to the particle image captured by PTV experiment, the author has proposed a new preprocessing method to provide a more reliable particle image for the calculation of the flow field motion in the later stage.

PTV experiments and DEM simulations of the coefficient of restitution for irregular particles impacting on horizontal substrates

For systems of particles with irregular shapes, the collisions between particles and between particles and walls are highly complex and strongly related to the contact geometry. In this work, the collision behavior between irregular maltodextrin particles (with a characteristic size of approximately 100 μm) and horizontal substrates was experimentally measured by an improved particle tracking velocimetry (PTV), which simultaneously reconstructed the trajectories of many particles during the process of free fall and rebound. In addition, the measurement data were compared with DEM simulations using the multi-sphere model and the superquadric model, regarding the distributions of total and normal coefficients of restitution and corresponding relationships with the rotational speed after collision and the absolute difference of incidence angle and rebound angle. Compared to the superquadric model, the multi-sphere model well predicts the macroscopic particle-wall collision behaviors of irregular non-convex particles.

Probing flow-induced nanostructure of complex fluids in arbitrary 2D flows using a fluidic four-roll mill (FFoRM)

Engineering flow processes to direct the microscopic structure of soft materials represents a growing area of materials research. In situ small-angle neutron scattering under flow (flow-SANS) is an attractive probe of fluid microstructure under simulated processing conditions, but current capabilities require many different sample environments to fully interrogate the deformations a fluid experiences in a realistic processing flow. Inspired by recent advances in microfluidics, we present a fluidic four-roll mill (FFoRM) capable of producing tunable 2D flow fields for in situ SANS measurements, that is intended to allow characterization of complex fluid nanostructure under arbitrary complex flows within a single sample environment. Computational fluid dynamics simulations are used to design a FFoRM that produces spatially homogeneous and sufficiently strong deformation fields. Particle tracking velocimetry experiments are then used to characterize the flows produced in the FFoRM for several classes of non-Newtonian fluids. Finally, a putative FFoRM-SANS workflow is demonstrated and validated through the characterization of flow-induced orientation in a semi-dilute cellulose nanocrystal dispersion under a range of 2D deformations. These novel experiments confirm that, for steady state straining flows at moderate strain rates, the nanocrystals orient along the principal strain-rate axis, in agreement with theories for rigid, rod-like Brownian particles in a homogeneous flow.

Exploration of thermal counterflow in He II using particle tracking velocimetry

Visualization of thermal counterflow in He II using PIV (particle image velocimetry) and PTV (particle tracking velocimetry) is difficult because tracer particle motion can be influenced by both the normal fluid and superfluid components of He II as well as the quantized vortex tangle. For instance, an early PTV experiment observed particles moving at the normal fluid velocity $v_n$, while a PIV experiment observed particles moving at $v_n/2$, though the range of heat flux applied in these experiments differed by an order of magnitude. To resolve this apparent discrepancy and explore statistics of particle motion in thermal counterflow, we have applied PTV to a wide range of heat flux at several fluid temperatures. We introduce a scheme for analyzing the velocity of particles presumably moving with the normal fluid separately from those presumably influenced by the vortex tangle. Our results show two distinct peaks in the streamwise particle velocity PDF (probability density function) for lower heat flux, one centered at the normal fluid velocity $v_n$ ("G2") and one near $v_n/2$ ("G1"). For higher heat flux there is a single peak centered near $v_n/2$ ("G3"). Using our separation scheme we show there is no size difference between particles contributing to G1 and G2. We also show that non-classical features of the transverse velocity PDF arise entirely from G1, while the corresponding PDF for G2 exhibits classical Gaussian form. G2 transverse velocity fluctuation, backed up by second sound attenuation in decaying counterflow, suggests large scale turbulence in the normal fluid is absent from the two peak region. We offer a brief discussion of physical mechanisms that may be responsible for our observations, revealing that G1 velocity fluctuations may be linked to fluctuations of vortex line velocity, and suggest numerical simulations that may reveal underlying physics in detail.

An experimental study of the dynamics of saltation within a three-dimensional framework

Abstract Our understanding of aeolian sand transport via saltation lacks an experimental determination of the particle borne kinetic energy partitioned into 3 dimensions relative to the mean flow direction. This in turn creates a disconnect between global wind erosion estimates and particle scale processes. The present study seeks to address this deficiency through an extended analysis of data obtained from a series of particle tracking velocimetry experiments conducted in a boundary layer wind tunnel under transport limited conditions. Particle image diameter, as it appeared within each camera frame, was extensively calibrated against that obtained by sieving, and the ballistic trajectories detected were disassembled into discrete particle image pairs whose distribution and dynamics were then examined in vertical profile with sub-millimeter resolution. The vertical profile of the wind aligned particle transport rate was found to follow a power relation within 10 mm of the bed surface. The exponent of this power function changes with increasing spanwise angle (θ) to produce a family of curves representing particle diffusion in 3 dimensions. Particle mass was found to increase with θ, and the distribution of the total particle kinetic energy was found to be very similar to that for the particle concentration. The spanwise component of the kinetic energy of a saltating particle peaks at θ = 45°, with the stream-aligned component an order of magnitude higher in value. Low energy, splashed particles near the bed account for a majority of the kinetic energy distributed throughout the particle cloud, regardless of their orientation.

µ-Particle tracking velocimetry and computational fluid dynamics study of cell seeding within a 3D porous scaffold.

Cell seeding of 3D scaffolds is a critical step in tissue engineering since the final tissue properties are related to the initial cell distribution and density within the scaffold unit. Perfusion systems can transport cells to the scaffold however; the fact that cells flow inside the scaffold pores does not guarantee cell deposition onto the scaffold substrate and cell attachment. The aim of this study was to investigate how fluid flow conditions modulate cell motion and deposition during perfusion. For such a purpose, a multiphase-based computational fluid dynamics (CFD) model was developed in conjunction with particle tracking velocimetry experiments (PTV) which for the first time were applied to observe cell seeding inside a 3D scaffold. CFD and PTV results showed the strong effect of gravity for lower flow rates leading to cell sedimentation and poor transport of cells to the scaffold. Higher flow rates help overcome the effect of gravity so more cells travelling inside the scaffold were found. Nonetheless, fluid flow drags cells along the fluid streamlines without intercepting the scaffold substrate. As a consequence, if cells do not deposit into the scaffold substrate, cell adhesion cannot occur. Therefore, cell-scaffold interception should be promoted and the present computational model which predicts the effect of gravity and fluid drag on cells trajectories could serve to optimise bioreactors and enhance cell seeding efficiency.

Study of Particle Motion in He II Counterflow Across a Wide Heat Flux Range

Some discrepancy exists in the results of He II counterflow experiments obtained using particle image velocimetry (PIV) when compared with those obtained using particle tracking velocimetry (PTV): using PIV, it was observed that tracer particles move at roughly half the expected normal fluid velocity, \(v_n/2\), while tracer particles observed using PTV moved at approximately \(v_n\). A suggested explanation is that two different flow regimes were examined since the range of heat flux applied in each experiment was adjacent but non-overlapping. Another PTV experiment attempted to test this model, but the applied heat flux did not overlap with any PIV experiments. We report on the beginnings of a study of solid \(\hbox {D}_2\) particle motion in counterflow using PTV, and the heat flux range overlaps that of all previous visualization studies. The observed particle velocity distribution transitions from a two-peak structure to a single peak as the heat flux is increased. Furthermore, the mean value of one peak in the bi-modal distributions grows at approximately the same rate as \(v_n\), while the mean value of the single-peak distributions grows at roughly \(0.4v_n\), in reasonable agreement with both previous experiments and with the suggested model.

Experimental study of flow field characteristics on bed configurations in the pebble bed reactor

The flow field characteristics are of fundamental importance in the design work of the pebble bed high temperature gas cooled reactor (HTGR). The different effects of bed configurations on the flow characteristics of pebble bed are studied through the PTV (Particle Tracking Velocimetry) experiment. Some criteria, e.g. flow uniformity (σ) and mass flow level (α), are proposed to estimate vertical velocity field and compare the bed configurations. The distribution of the Δθ (angle difference between the individual particle velocity and the velocity vector sum of all particles) is also used to estimate the resultant motion consistency level. Moreover, for each bed configuration, the thickness of displacement is analyzed to measure the effect of the funnel flow zone based on the boundary layer theory. Detailed information shows the quantified characteristics of bed configuration effects on flow uniformity and other characteristics; and the sequence of levels of each estimation criterion is obtained for all bed configurations. In addition, a good design of the pebble bed configuration is suggested and these estimation criteria can be also applied and adopted in testing other geometry designs of pebble bed.

Measurement and analysis of the internal flow field in the hydrodynamic torque converter with adjustable guide vanes

This article presents a particle-tracking velocimetry experiment for studying internal flows of hydrodynamic torque converter whose guide vanes are adjustable. The torque converter in which the flow region is an enclosed space with multiple impellers has a complicated geometry of impellers. Complex flows in adjustable stator are experimentally analyzed using particle-tracking velocimetry, and some advanced measurement technique has been successfully applied. Under each opening, using the single-frame and triple-exposure method, images of the flow fields in the adjustable stator were recorded at three typical working conditions as the speed ratios were equal to 0 (stall), 0.5 (design), and 1 (idle). According to particle trajectories on the images, the displacements and corresponding velocity vectors were obtained. The internal flow pattern of the hydrodynamic torque converter with adjustable guide vanes were acquired and analyzed in two cases: the changing conditions under the same opening and the changing openings under the same condition.

Viscous tilting and production of vorticity in homogeneous turbulence

Viscous depletion of vorticity is an essential and well known property of turbulent flows, balancing, in the mean, the net vorticity production associated with the vortex stretching mechanism. In this letter, we, however, demonstrate that viscous effects are not restricted to a mere destruction process, but play a more complex role in vorticity dynamics that is as important as vortex stretching. Based on the results from three dimensional particle tracking velocimetry experiments and direct numerical simulation of homogeneous and quasi-isotropic turbulence, we show that the viscous term in the vorticity equation can also locally induce production of vorticity and changes of the orientation of the vorticity vector (viscous tilting).

PTV experiments of subcooled boiling flow through a vertical rectangular channel

Time resolved Particle Tracking Velocimetry (PTV) experiments were carried out to investigate turbulent, subcooled boiling flow of refrigerant HFE-301 through a vertical rectangular channel with one heated wall. Measurements were performed with liquid Reynolds numbers (based on the hydraulic diameter) of Re = 3309, 9929 and 16,549 over a wall heat flux range of 0.0–64.0 kW/m 2. Turbulence statistics are inferred from PTV full-field velocity measurements. Quantities such as: instantaneous 2D velocity fields, time-averaged axial and normal velocities, axial and normal turbulence intensities, and Reynolds stresses are obtained. The present results agree well with previous studies and provides new information due to the full-field nature of the technique. This work is an attempt to provide turbulent subcooled boiling flow data for validation and improvement of two-phase flow computational models.

Dynamic neutron computer tomography technique forvelocity measurement in liquid metal flow- Fundamental PTV experiment -

The aim of this development is to visualize and measure the velocity distribution inliquid metal flow using the neutron beam with the high-speed imaging technique, computertomography (CT) technique and particle tracking velocimetry (PTV). Final research purpose isto obtain the velocity distribution and flow profile data of liquid metal flow in a heated rodbundle for development of the advanced fast breeder reactor (FBR) core. In this paper,visualization and measurement method using the high intensity and large size neutron beamport of the research reactor JRR-4, design and manufacturing of the experimental apparatus,spring model PTV method for this technique and results of the fundamental PTV experimentwere reported. The test section for the fundamental experiment was a revolving aluminumcolumn with cadmium tracers which simulated the liquid metal flow. As the result, cadmiumtracers buried in the column with the speed of 1.5 revolving per second could be visualized asthe 3D movie under 125Hz and 250Hz sampling conditions, the profile of the tracer could betraced, and fundamental velocity distribution measurement method could be conformed.