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Presence of mucus layer and inlet air temperature variations can significantly affect the extent of particle transport and deposition in the mouth-throat airway for aerosol drug delivery applications. In addition, higher inlet air temperature can lead to thermal injuries as well. The main goal of the present paper is to investigate these effects in a highly idealized mouth-throat geometry in detail. Large eddy simulation was performed to accurately predict the air flow-fields and a Lagrangian particle tracking model has been employed to capture the particle deposition efficiencies and patterns. The effects of three different inlet air temperatures (15 °C, 26.7 °C and 45 °C) and three different particle sizes (3 μm, 5 μm and 6 μm) have been studied for inlet flow rates of 15 L/min and 30 L/min with and without mucus layer in the present investigation. Detailed velocity and temperature fields, as well as, particle deposition efficiencies and patterns were analyzed and it has been found out that (a) the particle deposition efficiencies varied significantly with changes in inlet air temperature and flow rates, particle diameters and in the presence of mucus layer, (b) the presence of recirculation zones and secondary vortices determined the rate of particle deposition at different inhalation flow rates and inlet air temperatures, and (c) the changes in temperature distribution near the mouth-throat wall in the presence of mucus layer have a dominant effect on particle deposition as compared to inertial deposition. The findings of the present work will provide useful information in understanding the heat transfer effects on particle transport and deposition for the design of pulmonary drug delivery devices under the influence of various environmental and human factors.

Aircraft-mounted gas turbine engines may need to employ a variety of inlet ducts to perform various missions. An inertial particle separator (IPS) is a type of inlet duct that can remove harmful du...

Direct impingement (DI) erosion testing of steel and cobalt-based alloys is conducted with particles entrained in air and water. The tests are performed using 75- and 300-μm silica particles with three particle velocities and five impact angles. The mass loss results are used to develop an empirical equation that contains an explicit exponential term for the particle size effect. The erosion equation obtained from the gas jet experiments is implemented into a CFD solver with Lagrangian particle tracking for the liquid-submerged geometry. The CFD-based erosion predictions agree fairly with the experimental measurement for both particles. Strong effect has been observed for the exponential correction term in the erosion equation for liquid-solid flow cases; particularly with small particles at low impact velocities.

This paper develops a novel approach for evaluating charged particles' collision probability in the external electric field of a regular two-stage electrostatic precipitator based on Lagrangian particle tracking method, which overcomes itself difficulties and that of the Eulerian method. The numerical simulation aims to obtain the particles' accumulated displacement which is a parameter to reflect the efficiency of particle collision. The effect factors of frequency, gas velocity, plate spacing and applied voltage are also considered. Results indicate that the external electric field of R-AC is more beneficial to particle collision compared to the other waveforms of AC. Besides, frequency and plate spacing are not found to have obvious or regular effect on collision probability, but the promotion effect of applied voltage on it was obtained. The dimensionless coefficient analysis provides extremely useful information for the optimization of working conditions in different types of the external electric field.

Particle-laden turbulent flow under saturated electrostatic field in 90-degree bend pipe at Reb = 58000 is investigated using one-way coupled Large Eddy Simulation (LES) with a Lagrangian particle tracking technique. Drag, lift, buoyancy, gravity, and electrostatic force are considered. Three particle sizes (dp = 5, 10, 50 μm, St = 5.47, 21.91, 547) are considered. The results show that particle concentration is higher in outer bend than that in inner bend and the concentration increases with particle size. At the stagnation point of Dean vortices near the inner arc of bend, particle concentration is significantly increased under the synergy effect of electrostatics and secondary flow. In addition, particles trapped in the viscous layer are difficult to resuspend under electrostatic effect. Particle concentration near the wall under the presence of electrostatics is larger than that under the absence of electrostatics. However, at the bend, particle concentration in the core region under the presence of electrostatics is lower than that in the absence of electrostatics. For particle behavior, drag force plays the most important role in the core region while electrostatic force dominates the near wall region and causes particles to accumulate there.

Multidimensional numerical simulations are performed to investigate the evolution and formation of unburned fuels for a shock–fuel jet interaction scenario. A full set of Navier–Stokes equations wi...

The present study aims to investigate the effect of swirling flow on particle deposition in a realistic human airway. A computational fluid dynamic (CFD) model was utilized for the simulation of oral inhalation and particle transport patterns, considering the k-ω turbulence model. Lagrangian particle tracking was used to track the particles’ trajectories. A normal breathing condition (30 L/min) was applied, and two-micron particles were injected into the mouth, considering swirling flow to the oral inhalation airflow. Different cases were considered for releasing the particles, which evaluated the impacts of various parameters on the deposition efficiency (DE), including the swirl intensity, injection location and pattern of the particle. The work's novelty is applying several injection locations and diameters simultaneously. The results show that the swirling flow enhances the particle deposition efficiency (20–40%) versus no-swirl flow, especially in the mouth. However, releasing particles inside the mouth, or injecting them randomly with a smaller injection diameter (dinj) reduced DE in swirling flow condition, about 50 to 80%. Injecting particles inside the mouth can decrease DE by about 20%, and releasing particles with smaller dinj leads to 50% less DE in swirling flow. In conclusion, it is indicated that the airflow condition is an important parameter for a reliable drug delivery, and it is more beneficial to keep the inflow uniform and avoid swirling flow.

Shock tube experiments are a cornerstone of investigations into the hypersonic flight environment. However, the actual flow through the basic shock tube has not been well characterized in the literature, and nonuniformities arising in the test gases are not well understood. This work produces a quasi-one-dimensional analytical methodology for predicting the nonuniformities in the postshock test gas based exclusively on the experimentally measured history of shock speed down the tube. Wave effects extracted from shock speed variations are shown to provide all information necessary in order to reconstruct the test slug from any particular experiment. Accurate representation of flow dynamics is initially checked against argon test cases following accelerating and decelerating shock trajectories, each with a tube-end Mach number of 6.5 and a fill pressure of 66.66 Pa in a tube of 100 mm diameter. Agreement between the method and results from a viscous, axisymmetric Navier–Stokes solution is found to be within 1% in pressure and temperature.

An axisymmetric viscous shock tube simulation code is developed that keeps the shock and the contact discontinuity stationary in suitably constructed moving frames of reference. The flowfield aroun...

Reduced order models for ignition analysis can offer insights into ignition processes and facilitate the combustor optimization. In this study, a Pairwise Mixing-Reaction (PMR) model is formulated to model the interaction between the flame particle and the surrounding cell mixture during Lagrangian flame particle tracking. Specifically, the model accounts for the two-way coupling of mass and energy between the flame particle and the surrounding shell layer by modelling the corresponding turbulent mixing, chemical reaction and evaporation process if present. The state of a flame particle, e.g., burnt, hot gas or extinguished, is determined based on particle temperature. This model can properly describe the ignition process with a spark kernel being initiated in a nonflammable region, which is of practical importance in certain turbine engines and has not been rigorously accounted for by the existing models based on the estimation of local Karlovitz number. The model is integrated into an ignition probability analysis platform and is demonstrated for a methane/air bluff-body flame with the flow and fuel/air mixing characteristics being extracted from a non-reacting simulation. The results show that for the spark location being at the extreme fuel-lean outer shear layer of the recirculation zone, PMR can yield ignition events with a significant number of active flame particles. The mechanisms for the survival of the initial flame particles and the entrainment of the survived flame particles into the recirculation zone are analyzed. The results also show that the ignition probability map from PMR agrees well with the experimental observation: a high ignition probability in the shear layer of the recirculation zone near the mean stoichiometric surface, and low ignition probabilities inside the recirculation zone and the top stagnation region of the recirculation zone. The parametric study shows that the predicted shape of the ignition progress factor and ignition probability is in general insensitive to the model parameters and the model is adequate for quantifying the regions with high ignition probabilities.

A forced ignition probability analysis method is developed for turbulent combustion, in which kernel formation is analyzed with local kernel formation criteria, and flame propagation and stabilization are simulated with Lagrangian flame particle tracking. For kernel formation, the effect of turbulent scalar transport on flammability is modelled through the incorporation of turbulence-induced diffusion in a spherically outwardly propagating flame kernel model. The dependence of flammability limits on turbulent intensities is tabulated and serves as the flammability criterion for kernel formation. For Lagrangian flame particle tracking, flame particles are tracked in a structured grid with flow fields being interpolated from a Computational Fluid Dynamics (CFD) solution. The particle velocity follows a Langevin model consisting of a linear drift and an isotropic diffusion term. The Karlovitz number is employed for the extinction criterion, which compares chemical and turbulent timescales. The integration of the above two-step analysis approach with non-reacting CFD is achieved through a general interpolation interface suitable for general unstructured CFD grids. The method is demonstrated for a methane/air bluff-body flame, in which flow and fuel/air mixing characteristics are extracted from a non-reacting simulation. Results show that the computed ignition probability map agrees qualitatively with experimental results. A reduction of the ignition probability in the recirculation zone and a high ignition probability on the shear layer of the recirculation zone near the mean stoichiometric surface are well captured. The tools can facilitate optimization of spark placement and offer insights into ignition processes.

In this paper, a novel approach based on the Lagrangian particle tracking method which adopted the accumulated displacement of particles as judgment standard was proposed to investigate the particle collision mechanism under the influence of non-contact external forces in a typical wire-plate electrostatic precipitator. The accumulated displacement of different diameter particles could reflect the range of particle motion and the collision probability inside the ESP, which was obtained from the calculated trajectory coordinates of particles under the influence of Brownian force and electric force. Results showed that the electric force controlled the particle’s trajectory direction while the Brownian force only made particles fluctuate along with the main track. The binary collision models with the determination of the dominant force were developed, which can be divided into two areas respectively called the electric force dominant region and the Brownian force dominant region. The total accumulated displacement of the submicron particle presented a U-shape curve, which matched well with the grade collection efficiency of fine particles in various experiments and demonstrated the validity of the proposed method. Also, the approach had good expansibility in investigating the role of other external forces in particle collision and could provide references for the design and working condition selection of ESP.

To respond to the ongoing pandemic of SARS-CoV-2, this contribution deals with recently highlighted COVID-19 transmission through respiratory droplets in form of aerosols. Unlike other recent studies that focused on airborne transmission routes, this work addresses aerosol transport and deposition in a human respiratory tract. The contribution therefore conducts a computational study of aerosol deposition in digital replicas of human airways, which include the oral cavity, larynx and tracheobronchial airways down to the 12th generation of branching. Breathing through the oral cavity allows the air with aerosols to directly impact the larynx and tracheobronchial airways and can be viewed as one of the worst cases in terms of inhalation rate and aerosol load. The implemented computational model is based on Lagrangian particle tracking in Reynolds-Averaged Navier–Stokes resolved turbulent flow. Within this framework, the effects of different flow rates, particle diameters and lung sizes are investigated to enable new insights into local particle deposition behavior and therefore virus loads among selected age groups. We identify a signicant increase of aerosol deposition in the upper airways and thus a strong reduction of virus load in the lower airways for younger individuals. Based on our findings, we propose a possible relation between the younger age related fluid mechanical protection of the lower lung regions due to the airway size and a reduced risk of developing a severe respiratory illness originating from COVID-19 airborne transmission.

An actuator surface model has been developed that couples an aerodynamics model to a computational fluid dynamics solver. The model is designed for simulation of rotors in complex operating environ...

Purpose: Computational Fluid Dynamics (CFD) simulations are performed to investigate the impact of adding a grid to a two-inlet dry powder inhaler (DPI). The purpose of the paper is to show the importance of the correct choice of closure model and modeling approach, as well as to perform validation against particle dispersion data obtained from in-vitro studies and flow velocity data obtained from particle image velocimetry (PIV) experiments. Methods: CFD simulations are performed using the Ansys Fluent 2020R1 software package. Two RANS turbulence models (realisable $k - \epsilon$ and $k - \omega$ SST) and the Stress Blended Eddy Simulation (SBES) models are considered. Lagrangian particle tracking for both carrier and fine particles is also performed. Results: Excellent comparison with the PIV data is found for the SBES approach and the particle tracking data are consistent with the dispersion results, given the simplicity of the assumptions made. Conclusions: This work shows the importance of selecting the correct turbulence modelling approach and boundary conditions to obtain good agreement with PIV data for the flow-field exiting the device. With this validated, the model can be used with much higher confidence to explore the fluid and particle dynamics within the device., Comment: Accepted in Pharmaceutical Research (2021)

A three-dimensional numerical model has been developed to quantify the predominant phenomena roles on dynamics alumina particles between an electrolytic bath and the vicinity of gas bubbles. At the particle scale, the bath, regarded as turbulent flow, was modeled by a steady plane shear flow and solved using a lattice Boltzmann method. The coupling between the fluid and particle phases is carried out using an immersed boundary method to tackle the interface. This numerical scheme resolves the hydrodynamic perturbation induced by the alumina particles, and hence their interactions are described by Lagrangian particle tracking. The hydrodynamic effects combined with mechanical and thermal responses on the computation of the fluid system's stress intensity factors were investigated. An excellent convergence and accuracy were achieved for the transport and interaction of the alumina particle model.

The understanding of flame holding mechanism is very important for combustor design. To elucidate the flame holding mechanism at the injector exit in liquid rocket engines, it is indispensable to know the underlying physics of trans-critical mixing process, because the flame holding location is exactly where trans-critical mixing process, which is still veiled, takes place. In the present paper, a new Large Eddy Simulation (LES) method is developed by gaining deeper physical insights into possible sub-grid-scale (SGS) thermodynamic and fluid dynamic instabilities excitable at thin large-density-gradient-magnitude portions to describe trans-critical processes. The presence of thin large-density-gradient-magnitude portions in trans-critical mixing process is troublesome for numerical stability of supercritical fluid flow LES from various points of view. Our idea is to utilize an SGS model functioning at the crossover between the liquid-like and gas-like supercritical fluids in a hybrid scheme of Lagrangian particle tracking and two-phase flow LES. Reduced dynamic viscosity at high pressure may cause SGS thermodynamic and hydrodynamic instabilities in the trans-critical mixing flow field. They are (1) phase separation due to thermodynamic instability, (2) Landau's hydrodynamic instability occurring at the pseudo-boiling location within a heated injector, and (3) Rayleigh–Taylor instability at the pseudo-boiling location, which is induced by Kelvin–Helmholtz instability vortices. These are analyzed and organized into new SGS models characterizing the trans-critical jet mixing process.

A major challenge in the operation and development of the high-head water resources, especially in the mountains with high sediment yield, is the erosion of Pelton turbine components. In this work, a numerical study was carried out based on sediment properties measured in field conditions, such as particle distributions and concentrations, to analyze the erosion mechanism of a prototype Pelton turbine injector. The Volume of Fluid (VOF) method was combined with a Lagrangian particle tracking approach to simulate the air-water-sediment flow, followed by the application of Mansouri’s model to estimate the erosion. The predicted erosion patterns were in good agreement with field observations, especially in physically reproducing the asymmetrical erosion distribution on the needle surface. To elucidate this asymmetry, fundamental analysis of the flow patterns including the vortex structures and the secondary flow on the particle behaviors was carried out. Interestingly results were found about the secondary flow induced by the von Karman vortex shedding, which increased the particle separations, and consequently, enhanced the erosion in shedding areas. The current work may provide important engineering insights to reduce erosion of components with inner obstructions.

The influence of particle concentration on the drag force of a particle deserves attention when using the Lagrangian Particle Tracking methods for the prediction of industrial type gas-solid flows. The Lagrangian approach is best suited to applications where the solids volume fraction is low, and the effect of particle concentration can be ignored. In the present work, a 3D time dependent numerical analysis is performed to study the effect of Lagrangian model improvements to replicate experimental studies of straight horizontal pipe flow and flow through a 90° horizontal-to-vertical bend. The present predictions are compared with published experimental data of Tsuji and Morikawa (1982) , and Yilmaz (1997) . Special attention is paid to influence of particle mass-flow rates and conveying velocity on the particle motion within the system. This study used a CFX-4 package, where the ability to modify the code was necessary to include particle model improvements. These improvements included implementing a newly drag force model developed as a part of this research work. Particle-wall collision and particle-particle collision models developed by Sommerfeld (1992) , and Sommerfeld (2001) are also implemented in the CFD model. The standard k–e dispersed turbulence model was utilized as the predictions for the gas phase only gave similar predicted axial velocity compared to the more computationally demanding Reynolds stress model. The results showed that the inclusion of the various improvements lead to reasonable predicted particle velocities in both the upper and lower regions of the straight horizontal pipe which denote the dilute and dense regions respectively. It was also found that the inclusion of the rough-wall particle wall collision model decreases the axial particle velocity in the lower region where the bulk of the particle wall collisions occur. While the inclusion of the particle collision models tends to disperse the particles away from the lower region resulting in a less dense lower section and a distinctly more homogenous particle distribution compared with the standard model predictions. Further, the increase in particle concentration leads to a reduction in axial velocity due to a loss of momentum through particle-wall and particle-particle collisions. Finally, the improved CFD model best predicted both the reduction and increase in the particle velocities in the different regions.

Arrays of surface ribs have been reported to significantly enhance particle collection efficiency in particle removal devices. However, the surface ribs also cause a higher pressure drop. Therefore, the overall performance needs to take into consideration the above factors. In this study, different forms of surface ribs inspired by nature were designed and parametric studies were performed to enhance deposition efficiency. Our parametric studies comprised three different aspects: geometry of the patterned surface, pitch-to-height ratio, and particle size. The flow field around patterned surfaces was simulated in a two-dimensional channel flow by using the Reynolds stress model, corrected by turbulence velocity fluctuation in the wall-normal direction. The particle trajectory was solved by using Lagrangian particle tracking. When the overall efficiency ratio was considered, a semi-circular pattern had the best overall efficiency with 1137 times increase when compared to the case without patterns. Although the open-circular pattern has the minimum particle deposition enhancement, the overall efficiency of the open-circular pattern has 862 times increase compared to the case without patterns. Surface ribs (semi-circular, triangular and rectangular) can achieve a higher particle deposition velocity, but a higher flow resistance is generated compared with applying the open-circular surface ribs. The deposition location was then investigated for different surface ribs at different pitch-to-height ratios (p/e). This study shows that the semi-circular surface pattern should be recommended to enhance the overall performance of particle removal devices, especially for submicron particles.

The transport and deposition of nano-particles in annular pipe flows under laminar conditions were studied. The Lagrangian particle tracking method was used to simulate the Brownian diffusion of ultrafine solid particles in a three-dimensional domain. The effects of nano-particle size, flow rate, inner and outer pipe diameters, pipe length, and temperature were studied. The computational models for the deposition of nano-particles in tubular, as well as annular pipe flows, were validated. Furthermore, using the CFD simulations and the Lagrangian particle tracking results, a new correlation for evaluating the deposition fraction of nano-particles in annular pipe flows was developed. The presented results could provide guidelines for evaluating nano-particle transport and deposition in annular pipes.

The impact of normal stress-induced closure on fluid flow and solute transport in a single rock fracture is demonstrated in this study. The fracture is created from a measured surface of a granite rock sample. The Bandis model is used to calculate the fracture closure due to normal stress, and the fluid flow is simulated by solving the Reynold equation. The Lagrangian particle tracking method is applied to modeling the advective transport in the fracture. The results show that the normal stress significantly affects fluid flow and solute transport in rock fractures. It causes fracture closure and creates asperity contact areas, which significantly reduces the effective hydraulic aperture and enhances flow channeling. Consequently, the reduced aperture and enhanced channeling affect travel time distributions. In particular, the enhanced channeling results in enhanced first arriving and tailing behaviors for solute transport. The fracture normal stiffness correlates linearly with the 5th and 95th percentiles of the normalized travel time. The finding from this study may help to better understand the stress-dependent solute transport processes in natural rock fractures.

Oil dispersion under a deep-water plunging breaker of height 0.15 m was studied by coupling the Lagrangian particle tracking code (NEMO3D) with the population balance model (VDROP). The wave hydrodynamics obtained in Part I (Cui et al. in Environ Fluid Mech 2020 (in press)) was used as input. It was observed that droplet inertia and major forces on droplets significantly impacted the transport of oil droplets under wave conditions, and neglecting it caused less entrainment into the water column and horizontal spread of oil plume. For droplets less than 400 microns, the droplet size distribution (DSD) tended to follow a power-law distribution with an exponent close to − 2.3, which was consistent with earlier experimental observations by Delvigne and Sweeney (Oil Chem Pollut 4(4):281–310, 1988). The distribution of large size droplets evolved with time and showed agreement with a power-law distribution having an exponent of − 9.7 about 20 s after the passage of the wave train. Reducing the interfacial tension enhanced droplets breakup and increased the exponent of power-law distribution to − 6.1 for droplets smaller than 400 microns. It was also found that neglecting the vertical gradient of eddy diffusivity led to the accumulation of oil droplets in low eddy diffusivity regions at the bottom part of the wave breaker. The investigation herein could be used to obtain design values for breakers that could be used in oil spill models to predict the oil droplet size distribution.

The quadrature method of moments (QMOM) and method of moments with a lognormal particle size distribution (PSD) are applied to simulate a cloud of evaporating droplets in a vortex ring flow. Results predicted by both methods are compared for the cases with a sinusoidal and lognormal initial particle size distribution, using Lagrangian particle tracking as a reference solution. Spatial distributions of droplet number density obtained by different methods are shown to be in a qualitative agreement. The method of moments with a lognormal PSD overestimates disappearance of particles leading to the underestimation of droplet mean size and higher values of the variance of PSD. QMOM showed better agreement with the Lagrangian approach than the method of moments with a lognormal PSD.

The influence of particle concentration on the drag force of a particle deserves attention when using the Lagrangian particle tracking methods for the prediction of industrial type gas-solid flows. The Lagrangian approach is best suited to applications where the solids volume fraction is low and the effect of particle concentration can be ignored. The paper successfully predicted the available experimental findings on the effects of particle arrangements on drag force. These successful predictions lead to the development of a new coefficient of drag for particles in cluster. Then a combined experimental and numerical study of free-falling particles was carried out in this study to investigate the behaviour of particles in cluster. The new coefficient of drag proposed in this study was used in the numerical simulations. The study highlighted the increase in terminal velocities of particles within cluster streams. The numerical simulations, obtained with the newly proposed coefficient of drag, showed improved results for the average size particles used. The improvements obtained for larger particle size particles were not as impressive.

Combustion process inside kerosene-GOx rocket combustor with kerosene film cooling is studied, and a modeling approach is proposed. The paper suggests to use the Lagrangian particle tracking technique to model fuel film behavior while the continuous fluid is simulated via the Navier-Stokes system of Favre-averaged equations. The approach is validated over the 12 experimental regimes by the criterions of characteristic velocity and pressure. The numerical study of film mass flow using the applied methodology shows significant influence on the adiabatic wall temperatures and relatively low impact on the pressure. In general, due to the application of the Lagrangian tracking and mostly simple models for main physical phenomena, the calculation of operational processes becomes fast and robust yet precise enough for engineering studies, which is helpful for parameterized routine calculations during the design process.

The objective of this work is to evaluate the capability of different combinations of a turbulence model and a Lagrangian particle tracking (LPT) model integrating a particle-wall interaction (PWI) model to predict particle-laden flow in 90-deg bends, as well as the impact of the PWI model on the prediction of the referred flow. The experimental data from Kliafas and Holt (1987) (LDV measurements of a turbulent air-solid two-phase flow in a 90° bend. Experiments in Fluids, 5: 73-85) concerning a vertical to horizontal square-sectioned duct with a hydraulic diameter of 0.1 m that are connected by a 90-deg bend with a curvature ratio of 3.52, served as the benchmark for the aimed analysis. Air with glass spheres of 50 μm diameter flows in the experimental duct system with a Reynolds number of 3.47×105. The airflow was modelled by four different turbulence models: a low Reynolds number k-e model, the SST k-ω model, the v2-f model, and the RSM SSG model. The particle-phase was modelled by a LPT formulation, and the particle-wall interaction was calculated using four different models: Brauer, Grant & Tabakoff, Matsumoto & Saito and Brach & Dunn PWI models. The 3D simulation results of mean streamwise velocities from the sixteen RANS-LPT/PWI combinations were compared qualitatively and quantitatively to experimental and numerical data available in the literature. The four turbulence models produced errors for the gas-phase in the order of 8%. Concerning the particle-phase, the errors produced by all RANS-LPT/PWI combinations were below 4% for bend angles up to 15° and up to 18% for bend angles higher than 30°. The best results for the particle-phase were obtained with the SST k-ω and v2-f model combined with the LPT/Brauer or LPT/Brach & Dunn PWI models, which produced errors inferior to 14%.

Magnetic nanoparticles are researched intensively not only for biomedical applications, but also for industrial applications including wastewater treatment and catalytic processes. Although these particles have been shown to have interesting surface properties in their bare form, their magnetisation remains a key feature, as it allows for magnetic separation. This makes them a promising carrier for precious materials and enables recovery via magnetic fields that can be turned on and off on demand, rather than using complex (nano)filtration strategies. However, designing a magnetic separator is by no means trivial, as the magnetic field and its gradient, the separator dimensions, the particle properties (such as size and susceptibility), and the throughput must be coordinated. This is showcased here for a simple continuous electromagnetic separator design requiring no expensive materials or equipment and facilitating continuous operation. The continuous electromagnetic separator chosen was based on a current-carrying wire in the centre of a capillary, which generated a radially symmetric magnetic field that could be described using cylindrical coordinates. The electromagnetic separator design was tested in-silico using a Lagrangian particle-tracking model accounting for hydrodynamics, magnetophoresis, as well as particle diffusion. This computational approach enabled the determination of separation efficiencies for varying particle sizes, magnetic field strengths, separator geometries, and flow rates, which provided insights into the complex interplay between these design parameters. In addition, the model identified the separator design allowing for the highest separation efficiency and determined the retention potential in both single and multiple separators in series. The work demonstrated that throughputs of ~1/4 L/h could be achieved for 250–500 nm iron oxide nanoparticle solutions, using less than 10 separator units in series.

Crud has been observed on the fuel rod surfaces in a variety of fuel designs around the world, and in some limited situations fuel performance was compromised due to crud-induced power shift (CIPS) and/or crud-induced localized corrosion (CILC). It is generally believed that crud deposition depends on fuel rod surface sub-cooled nucleate boiling, coolant chemistry and the availability of particles from component corrosion or from reinserted fuel. The formation, release, and accumulation of crud on the fuel and its influence on CIPS and/or CILC is a complicated process involving multi-physics phenomena. This study uses Computational Fluid Dynamics (CFD) Lagrangian Particle Tracking (LPT) techniques in analysis of particle transfer behavior in fuel rod bundles focusing on flow swirl and turbulence impacts. It is hoped that high fidelity CFD results can provide insights into particle transfer behaviors in the bulk coolant as well as near the fuel rods, which may provide guidance for model development of lumped or integrated analysis methods. The CFD model was built based on the best practices learned from previous single-phase analyses. The LPT options, including particle injectors, forces on particles, and solver settings, were verified by comparing the simulated results to the test data from simple geometry with various particle sizes, covering deposition mechanisms in diffusion-, turbulent- and inertial-dominated regimes. The tested model then was applied to Westinghouse fuel designs with and without Intermediate Flow Mixing (IFM) grids. Particle concentration and size distributions in the coolant around fuel rods were obtained and the effects of grid induced swirl flow on particle transfer were identified. The analysis results may be included in lumped or integrated crud formation/release analysis methods. Limitations and potential improvements of this analysis method are also discussed.

Examining the behaviour of dense suspensions has proven to be difficult, both experimentally and numerically. Using super water–absorbent polymer, PIV measurement was successfully conducted in a hydrogel suspension with a volume fraction (VF) of Φ =20% (see Zhang and Rival, 2018). However, due to the slightly refractive index mismatch, the image quality will degrade significantly as the particle loading of the hydrogel is increased. In order to achieve flow measurements in suspensions with high volume fractions, non-optical based techniques such as ultrasound imaging velocimetry (UIV) should be implemented. UIV has been developed for fluid dynamics applications and embraced by many researchers to study fluid flows (Gurung and Poelma, 2016; Jeronimo et al., 2019). Although, UIV provides useful information about the flow physics, it is unable to provide Lagrangian quantities such as particle trajectories, which is a key parameter to study entrainment and particle-wall interactions.

An experimental methodology is proposed for the study of aeroelastic systems. The approach locally evaluates the forces involved in Collar’s triangle, namely aerodynamic, elastic, and inertial forces. The position of flow tracers as well as of markers on the object surface is monitored by a volumetric PIV system. From the recorded images, the flow tracers and surfare markers are separated based on their optical characteristics. The resulting images are then analysed by Lagrangian particle tracking. The inertial and elastic forces are obtained solely analysing the motion and the deformation of the solid object, whereas the aerodynamic force distribution is obtained via the pressure-from-PIV technique. Experiments are conducted on a benchmark problem of fluid-structure interaction, featuring a flexible panel installed at the trailing edge of a cylinder. A polynomial fit of the markers’ positions is carried out to determine the panel’s instantaneous shape, from which the inertial and elastic forces are evaluated. The pressure loads on the panel are determined via solution of the Poisson equation for pressure, imposing adaptive boundary conditions that comply with the panel. The simultaneous measurement of the three forces allows to assess the equilibrium of forces, and in turn to close Collar’s triangle.

Impinging jets are widely used for heat and mass transfer because they are applicable to any type of body and can be easily implemented. They are also used in various industrial fields and design techniques. Previous research investigated e.g. a jet impinging onto a flat surface. However, since most of the mechanical parts have curvature on their surface, it is necessary to study more detailed properties of the jet impinging on a curved surface using advanced measurements. Therefore, in this study, three-dimensional flow structures of a round jet impinging on a convex cylinder surface were measured using volumetric Lagrangian particle tracking (LPT).

Over a thousand animal species are capable of walking on the interface between air and water. These speciesinclude water striders, a family of insects from the order Hemiptera that has an almost unique ability to walk on the surface of the water without penetrating it. They achieve this outstanding feat by making use of the surface tension and their long hydrophobic legs. Experiments have revealed that water striders transfer some momentum to the underlying fluid through capillary waves and hemi-spherical vortices and that both waves and vortices contribute to the mechanism of propulsion. However, the exact momentum and energy carried by waves and vortices have never been quantified together, and only the energy of the surface waves has been quantified to date. An analysis of the complete energy balance between the interface and the body of the water requires measurement of the free surface topography, together with the three-dimensional (3D) flow field in the water under the surface. The ultimate aim of this work was to develop a method capable of doing this.

Exhalation of small aerosol droplets and their transport, dispersion and (local) accumulation in closed rooms have been identified as the main pathway for indirect or airborne respiratory virus transmission from person to person, e.g. for SARS-CoV 2 or measles (Morawska and Cao 2020). Understanding airborne transport mechanisms of viruses via small bio-aerosol particles inside closed populated rooms is an important key factor for optimizing various mitigation strategies (Morawska et al. 2020), which can play an important role for damping the infection dynamics of any future and the ongoing present pandemic scenario, which unfortunately, is still threatening due to the spreading of several SARS-CoV2 variants of concern, e.g. delta (Kupferschmidt and Wadman 2021). Therefore, a large-scale 3D Lagrangian Particle Tracking experiment using up to 3 million long lived and nearly neutrally buoyant helium-filled soap bubbles (HFSB) with a mean diameter of ~ 370 µm as passive tracers in a 12 m³ generic test room has been performed, which allows to fully resolve the Lagrangian transport properties and flow field inside the whole room around a cyclically breathing thermal manikin (Lange et al. 2012) with and without mouth-nose-masks and shields applied. Six high-resolution CMOS streaming cameras, a large array of powerful pulsed LEDs have been used and the Shake-The-Box (STB) (Schanz et al. 2016) Lagrangian particle tracking algorithm has been applied in this experimental study of internal flows in order to gain insight into the complex transient and turbulent aerosol particle transport and dispersion processes around seated breathing persons.

Rapid depressurization is a fluid phenomenon that occurs in many industrial and natural applications. Its behaviour is often complicated by the formation, propagation and interaction of waves. In this work, we perform computer simulations of the rapid depressurization of a gas–solid mixture in a shock tube. Our problem set-up mimics previously performed experiments, which have been historically used as a laboratory surrogate for volcanic eruptions. The simulations are carried out with a discontinuous Galerkin compressible fluid solver with four-way coupled Lagrangian particle tracking capabilities. The results give an unprecedented look into the complex multiphase physics at work in this problem. Different regimes have been characterized in a regime map that highlights the key observations. While the mean flow behaviour is in good agreement with experiments, the simulations show unexpected accelerations of the particle front as it expands. Additionally, a new lifting mechanism for gas bubble (void) growth inside the gas–solid mixture is detailed.

Most interfacial flows of practical interest typically involve length- and time-scales that span over several orders of magnitude. Their accurate modelling, using interface-capturing or interface-tracking methods, therefore presents a prohibitively large computational cost. Over the past few years, hybrid Eulerian-Lagrangian approaches have been proposed with the aim to predict the behaviour of such flows both efficiently and accurately. These approaches rely on the assumption that small detached interfacial structures are spherical due to the dominant influence of surface tension, therefore allowing for their modelling using classical Lagrangian particle tracking techniques. The dynamics of large interfacial structures are thus fully resolved on the Eulerian grid, whereas the smaller interfacial structures, resulting from breakup instances, are transferred to a Lagrangian frame of reference and tracked as point-particles. In doing so, a main issue arises due to the competing requirements of both the Eulerian and Lagrangian approaches: on one hand, interfacial structures modelled with the Eulerian approach should be resolved by at least a few mesh cells; and on the other hand, Lagrangian particle tracking classically requires the tracked particles to be much smaller than the Eulerian mesh cells. Interfacial structures that lie between these two limits – typically shortly before and/or after their transfer from one framework to the other – are therefore poorly represented by any of the two approaches. So-far, a successful strategy to deal with this spatial paradox has not been proposed. To address this issue, a hybrid Eulerian-Lagrangian approach relying on an enhanced Lagrangian particle tracking method is proposed in this paper. Through the derivation of the filtered flow equations for a gas-droplets mixture, it is shown that the filtering of relevant quantities allows for the consistent tracking of Lagrangian particles that are of a similar size as, or larger than the Eulerian mesh cells. Numerical simulations of a particle settling under the influence of gravity are conducted to demonstrate the ability of the framework to accurately and consistently deal with Lagrangian particles that are larger than the Eulerian mesh cells. Finally, the full hybrid framework is tested on a realistic spray atomisation case, and the impact of the proposed filtering on the dynamics and the statistics of the spray is investigated.

Modern pore-scale modeling has the ability to simulate flow and particle (i.e., colloids, nanoparticles) transport at the pore- and particle-scale in realistic porous media. The pore-structure of a material can be obtained through x-ray micro tomography (XCT) or a similar three-dimensional (3D) imaging technique. From these data sets, fluid and particle transport can be simulated by direct numerical simulation of the fundamental equations of motion. In this paper, we employ the finite element method to simulate Stokes flow and, after the flow field is resolved, Lagrangian particle tracking (LPT) to track the fate and transport of nanoparticles (NPs). The presented methodology for direct numerical modeling allowed the simulation of NP transport in real materials (i.e., natural or engineered samples that experiments can be performed on rather than a computer-generated porous medium) in larger domains or with more particles than previous works. XCT images of a micromodel and a Berea sandstone were used as the computational domains to analyze the effect of particle diameter, attractive and repulsive surface forces, flow rate, surface capacity, and XCT image-based mineralogy on particle transport. In the micromodel simulations, in the presence of attractive surface forces, NP effluent recovery increased as particle diameter increased and as flow rate increased – findings qualitatively consistent with published experimental data. The use of XCT image-based mineralogy to spatially distribute attachment sites (i.e., clay) in the Berea showed no difference in particle retention when compared to a random distribution of attachment sites. These results are being used to help understand ongoing micromodel experiments and to design continuum-scale models of NP transport.

Particle deposition and resuspension in a horizontal, fully developed turbulent square duct flow at four flow bulk Reynolds numbers (10,320, 83k, 215k and 250k) is simulated by applying large eddy simulation coupled with Lagrangian particle tracking technique. Forces acting on particles includes drag, lift, buoyancy and gravity. Four particle sizes are considered with the diameters of 5 μm, 50 μm, 100 μm and 500 μm. Results obtained for the fluid phase are in good agreement with the available experimental and numerical data. Predictions for particles show that particle size, flow Reynolds number and the duct (celling, floor and vertical) walls play important roles in near-wall particle deposition and resuspension. For the smallest particle (5 μm), the particle deposition rates in duct ceiling, floor and vertical walls are found to be similar with each other and all increase with the flow Reynolds number, while the particle resuspension tends to occur in the middle wall regions and corners of the duct with less influenced by the flow Reynolds number. The ceiling deposition rate gradually decreases with particle size while the floor and vertical wall deposition rates both increase with particle size. The ceiling particle deposition rate increases with Reynolds number while the floor deposition rate decreases with it. The vertical deposition rate for the small particles (5–50 μm) increases with the flow Reynolds number obviously, while for the large particles (100–500 μm) that becomes insensitive. In addition, the flow Reynolds number is found to have an obvious effect on particle resuspension while the effect of particle size on particle resuspension decreases with Reynolds number. Eventually, a dynamic analysis was conducted for particles deposition and resuspension in turbulent duct flows.

The paper proposes a novel particle-wall collision model for calculating temporal changes of particle velocities and forces acting on the particle during the collision between an elastic particle and a plane solid wall. The purpose is to determine the maximum inertia force acting on the particle in connection with an accurate prediction of the transition between the sliding and non-sliding periods. This method is successfully applied to the calculation of drug detachment probability via particle-wall collisions within dry powder inhalers, in which fine drug particles are usually blended with larger carrier particles as one particle cluster for better dispersion. The present novel model is firstly verified in the micro-scale simulation of a single collision between the particle cluster and the wall. The simulation results reveal that the inertia force acting on drug particles is much larger than the fluid dynamic force and dominates the drug detachment. The detachment can occur through lift-off, sliding or rolling. Nearly half of the drug particles on the carrier surface can be detached by lift-off, and most of the remaining drug particles follow up with a sliding or rolling detachment. Based on these studies, a Lagrangian particle tracking algorithm is developed and is used to predict drug detachment probability within an inhaler device through one inhalation. By tracking 1024 particle clusters moving through the inhaler (i.e. the macro-scale simulation), the influence of different flow rates (i.e. 100 l/min and 70 l/min), friction coefficients between the carrier and the wall (i.e. 0.1 and 0.2), and carrier sizes (i.e. 100 μm and 500 μm) on drug detachment are investigated. The improved understanding of particle-wall collision detachment study will be the basis for optimising inhaler design.

Mixing is an important unit operation in the process industry. Ensuring homogeneity of slurry or emulsion is critical for subsequent processing or to improve the efficacy of reactions, and heat/mass transfer. Mixing in stirred tanks is typically improved through baffles. While baffles are good at breaking vortices, they contribute to energy dissipation. Most of the previous research focused on improving impeller designs, its position and operation. Limited investigations exist that probe the design improvements of baffles. In this work, through an extensive computational fluid dynamics study involving multi-phase flow simulations using volume of fluid (VOF) approach and Lagrangian particle tracking, we have designed an effective mixing system with optimum baffling. The newly designed baffle, called interface baffle, is placed at the interface between air and liquid to break the vortex and redirect the flow to the center. The predicted mixing behavior is experimentally validated in a pilot scale tank of 100 liter capacity. Particle size distribution measurements of samples from the top and the bottom of the tank were used to establish the effectiveness of mixing. Experiments were conducted under three different tank conditions, namely, without baffles, traditionally baffled, and interface baffled. Interface baffled system provided much better mixing characteristics.

In this study, flow structures and mixing performance in a blade-free planetary mixer, which combines rotation and revolution motions inside a cylindrical vessel, are numerically investigated. Flow fields in the mixer vessel are simulated in a single rotating reference frame with various revolution speeds and a fixed rotation speed. The mixing process is investigated by a Lagrangian particle tracking method and the mixing performance is evaluated based on particle concentration. The results of the numerical simulations show that a vortical flow with an axis inclined with respect to the rotation axis of the vessel is generated by the combined influence of the rotation and revolution motions. The flow structure and vortical flow intensity vary as a function of the precession rate, which is the ratio of the revolution speed to rotation speed. The mixing performance of the blade-free planetary mixer is found to be maximum at aspecific precession rate.

The impact of shear displacement under different mechanical boundary conditions on fluid flow and advective transport in a single fracture at the laboratory scale is demonstrated in the present study. The shear-induced changes of fracture aperture structures are determined by using the measured normal displacements and digitalized fracture surfaces from laboratory shear tests. Five shear tests on concrete replicas of the same fracture under different mechanical boundary conditions, including constant normal loading (CNL) and constant normal stiffness (CNS), are conducted to analyse the influence of mechanical boundary conditions on the shear-flow-transport processes. Fluid flow in the fracture with different shear displacements are simulated by solving the Reynolds equation. The Lagrangian particle tracking method is applied to model the advective transport in the fracture after shearing. The results generally show that the shear displacements and the normal loading conditions can significantly affect flow patterns and advective travel time distributions in the fracture. For mated fractures, the flow and transport will be enhanced by the increasing shear displacement because of shear dilation. For cases with the same shear displacement, the median advective travel time increases with the increasing boundary normal stiffness. The median advective travel time under the CNS boundary condition is generally longer than that under the CNL boundary condition. The results from this study can help to improve our understanding of stress-dependent solute transport processes in natural rock fractures.

Spatial regions that do not mix effectively with their surroundings and thus contribute less to the heat transport in fully turbulent three-dimensional Rayleigh-B\'{e}nard flows are identified by Lagrangian trajectories that stay together for a longer time. These trajectories probe Lagrangian coherent sets (CS) which we investigate here in direct numerical simulations in convection cells with square cross section of aspect ratio $\Gamma = 16$, Rayleigh number $Ra = 10^{5}$, and Prandtl numbers $Pr = 0.1, 0.7$ and $7$. The analysis is based on $N=524,288$ Lagrangian tracer particles which are advected in the time-dependent flow. Clusters of trajectories are identified by a graph Laplacian with a diffusion kernel, which quantifies the connectivity of trajectory segments, and a subsequent sparse eigenbasis approximation (SEBA) for cluster detection. The combination of graph Laplacian and SEBA leads to a significantly improved cluster identification that is compared with the large-scale patterns in the Eulerian frame of reference. We show that the detected CS contribute by a third less to the global turbulent heat transport for all investigated $Pr$ compared to the trajectories in the spatial complement. This is realized by monitoring Nusselt numbers along the tracer trajectory ensembles, a dimensionless local measure of heat transfer., Comment: 8 pages, 5 figures

The transport of virus-laden particles was investigated numerically in an archetypical supermarket configuration of area 1,200 m2 and ceiling height of 4.5 m. The particles were tracked u...

International audience; We develop a maximum likelihood method to infer relevant physical properties of elongated active particles. Using individual trajectories of advected swimmers as input, we are able to accurately determine their rotational diffusion coefficients and an effective measure of their aspect ratio, also providing reliable estimators for the uncertainties of such quantities. We validate our theoretical construction using numerically generated active trajectories upon no flow, simple shear, and Poiseuille flow, with excellent results. Being designed to rely on single-particle data, our method eases applications in experimental conditions where swimmers exhibit a strong morphological diversity. We briefly discuss some of such ongoing experimental applications, specifically, in the characterization of swimming E. coli in a flow.

The dispersion of oil droplets in rivers was numerically investigated for uniform flow in a hypothetical wide river with a depth of 3.0 m. The river hydrodynamics profile was used in conju...

When an infected person coughs, many virus-laden droplets will be exhaled out of the mouth. Droplets from deep lungs are especially infectious because the alveoli are the major sites of coronavirus replication. However, their exhalation fraction, size distribution, and exiting speeds are unclear. This study investigated the behavior and fate of respiratory droplets (0.1–4 μm) during coughs in a single-path respiratory tract model extending from terminal alveoli to mouth opening. An experimentally measured cough waveform was used to control the alveolar wall motions and the flow boundary conditions at lung branches from G2 to G18. The mouth opening was modeled after the image of a coughing subject captured using a high-speed camera. A well-tested k-ω turbulence model and Lagrangian particle tracking algorithm were applied to simulate cough flow evolutions and droplet dynamics under four cough depths, i.e., tidal volume ratio (TVR) = 0.13, 0.20. 0.32, and 0.42. The results show that 2-μm droplets have the highest exhalation fraction, regardless of cough depths. A nonlinear relationship exists between the droplet exhalation fraction and cough depth due to a complex deposition mechanism confounded by multiscale airway passages, multiregime flows, and drastic transient flow effects. The highest exhalation fraction is 1.6% at the normal cough depth (TVR = 0.32), with a mean exiting speed of 20 m/s. The finding that most exhaled droplets from deep lungs are 2 μm highlights the need for more effective facemasks in blocking 2-μm droplets and smaller both in infectious source control and self-protection from airborne virus-laden droplets.

Numerical studies of the wind-induced bias of precipitation measurements assume that turbulence is generated by the interaction of the airflow with the gauge body, while steady and uniform free-stream conditions are imposed. However, wind is turbulent in nature due to the roughness of the site and the presence of obstacles, therefore precipitation gauges are immersed in a turbulent flow. Further to the turbulence generated by the flow-gauge interaction, we investigated the natural free-stream turbulence and its influence on precipitation measurement biases. Realistic turbulence intensity values at the gauge collector height were derived from 3D sonic anemometer measurements. Large Eddy Simulations of the turbulent flow around a chimney-shaped gauge were performed under uniform and turbulent free-stream conditions, using geometrical obstacles upstream of the gauge to provide the desired turbulence intensity. Catch ratios for dry snow particles were obtained using a Lagrangian particle tracking model, and the collection efficiency was calculated based on a suitable particle size distribution. The collection efficiency in turbulent conditions showed stronger undercatch at the investigated wind velocity and snowfall intensity below 10 mm h&minus, 1, demonstrating that adjustment curves based on the simplifying assumption of uniform free-stream conditions do not accurately portray the wind-induced bias of snow measurements.

International audience; Thermal counterflow of superfluid 4 He is investigated experimentally, by employing the Particle Tracking Velocimetry technique. A flat heater, located at the bottom of a vertical channel of square cross-section, is used to generate this unique type of thermally driven flow. Micronic solid particles, made in situ, probe this quantum flow and their timedependent positions are collected by a digital camera, in a plane perpendicular to the heat source, away from the channel walls. The experiments are performed at relatively large heating powers, resulting in fluid velocities exceeding 10 mm/s, to ensure the existence of sufficiently dense tangles of quantized vortices. Within the investigated parameter range, we observe that the particles intermittently switch between two distinct motion regimes, along their trajectories, that is, a single particle can experience both regimes while traveling upward. The regimes can be loosely associated to fast particles, which are moving away from the heat source along almost straight tracks, and to slow particles, whose erratic upward motion can be said to be significantly influenced by quantized vortices. We propose a separation scheme to study the properties of these regimes and of the corresponding transients between them. We find that particles in both regimes display non-classical, broad distributions of velocity, which indicate the relevance of particlevortex interactions in both cases. At the same time, we observe that the fast particles move along straighter trajectories than the slow ones, suggesting that the strength of particle-vortex interactions in the two regimes is notably different.

The structural motion and unsteady aerodynamic loads of a pitching airfoil model that features an actuated trailing edge flap are determined experimentally using a single measurement and data processing system. This integrated approach provides an alternative to the coordinated use of multiple measurement systems for simultaneous position and flow field measurements in large-scale fluid–structure interaction experiments. The measurements in this study are performed with a robotic PIV system using Lagrangian particle tracking. Flow field measurements are obtained by seeding the flow with helium-filled soap bubbles, while the structural measurements are performed by tracking fiducial markers on the model surface. The unsteady position and flap deflection of the airfoil model are determined from the marker tracking data by fitting a rigid body model, that accounts for the motion degrees of freedom of the airfoil model, to the measurements. For the determination of the unsteady aerodynamic loads (lift and pitching moment) from the flow field measurements, two different approaches are evaluated, that are both based on unsteady potential flow and thin airfoil theory. These methods facilitate an efficient non-intrusive load determination on unsteady airfoils and produce results that are in good agreement with reference measurements from pressure transducers.