Lagrangian Tracking Research Articles

Divergence of the normalized wall shear stress as an effective computational template of low-density lipoprotein polarization at the arterial blood-vessel wall interface

Background and ObjectiveNear-wall transport of low-density lipoproteins (LDL) in arteries plays a relevant role in the initiation of atherosclerosis. Although it can be modelled in silico by coupling the Navier–Stokes equations with the 3D advection-diffusion (AD) equation, the associated computational cost is high. As wall shear stress (WSS) represents a first-order approximation of the near-wall velocity in arteries, we aimed at identifying computationally convenient WSS-based quantities to infer LDL near-wall transport based on the underlying near-wall hemodynamics in five models of three human arterial districts (aorta, carotid bifurcations, coronary arteries). The simulated LDL transport and its WSS-based surrogates were qualitatively compared with in vivo longitudinal measurements of wall thickness growth on the coronary artery models. MethodsNumerical simulations of blood flow coupled with AD equations for LDL transport and blood-wall transfer were performed. The co-localization of the simulated LDL concentration polarization patterns with luminal surface areas characterized by low cycle-average WSS, near-wall flow stagnation and WSS attracting patterns was quantitatively assessed by the similarity index (SI). In detail, the latter two represent features of the WSS topological skeleton, obtained respectively through the Lagrangian tracking of surface-born particles, and the Eulerian analysis of the divergence of the normalized cycle-average WSS vector field. ResultsConvergence of the solution of the AD problem required the simulation of 3 (coronary artery) to 10 (aorta) additional cardiac cycles with respect to the Navier-Stokes problem. Co-localization results underlined that WSS topological skeleton features indicating near-wall flow stagnation and WSS attracting patterns identified LDL concentration polarization profiles more effectively than low WSS, as indicated by higher SI values (SI range: 0.17–0.50 for low WSS; 0.24–0.57 for WSS topological skeleton features). Moreover, the correspondence between the simulated LDL uptake and WSS-based quantities profiles with the in vivo measured wall thickness growth in coronary arteries appears promising. ConclusionsThe recently introduced Eulerian approach for identifying WSS attracting patterns from the divergence of normalized WSS provides a computationally affordable template of the LDL polarization at the arterial blood-wall interface without simulating the AD problem. It thus candidates as an effective biomechanical tool for elucidating the mechanistic link amongst LDL transfer at the arterial blood-wall interface, WSS and atherogenesis.

Planar Interferometric Tracking of droplets in evaporating conditions

An effective Lagrangian Planar Interferometric Tracking (PIT) processor is proposed to track the size and path of multiple droplets, with spray droplet diameters (20–150 µm) and volumetric concentrations (approx300 drops/cm^3) consistent with industrial applications, produced by an ultrasonic atomiser in evaporating conditions. A test facility was developed where liquid droplets are exposed to a temperature gradient in a co-axial air flow, where the outer stream is preheated to the desired temperature (288–550 K). The PIT method builds on a TSI Global Sizing Velocimtery measurement technique and allows to detect, size and follow the path of droplets which were otherwise discarded or mis-analysed by the commercial software. The methodology was first tested under non-evaporating conditions, and multiple sources of errors, some common to most planar interferometric techniques, were identified and their order of magnitude and impact on final droplet measurement assessed. The main source of error is related to the out-of-plane motion of the droplets and the time they spend in the measurement volume. For non-evaporating conditions, measured data can be processed to filter out this source of error. In evaporating conditions, a novel method for assessing the impact of measurement error with respect to droplet evaporation and measurement timescales is defined. The PIT method allowed tracking of individual methanol droplets entrained within an airflow heated to 495 K and determining their size reduction under evaporating conditions. Measured droplet evaporation rates were then compared against those predicted by an iterative evaporation model, and a very good agreement was found between the modelled and measured estimates.Graphical abstract

Aggregation of microplastic and biogenic particles in upper-ocean turbulence

The aggregation of microplastic and biogenic particles in upper-ocean turbulence is studied by means of direct numerical simulations and Lagrangian tracking of point particles. The range of particle properties (size and density) and mixture characteristics (turbulence intensity and particle number densities) analyzed correspond to scenarios reminiscent of the problematic of microplastics in marine systems. A density ratio of 1.5 between the biogenic and microplastic particles, and varying diameter size and number density ratios are assumed. In particular, the focus is placed on the flow and mixture conditions encountered in the surface boundary layer (top region) of oceans, in which microplastics and biogenic particles have been experimentally observed to interact under significantly complex behaviors. The analysis consists of three principal parts involving the spatio-temporal distribution of the disperse and continuous phases, the mechanisms and rates of particle collisions, and the composition of the resulting aggregates. The main findings, for the range of parameters considered in this work and under the simplifying assumptions made in the model, are that (i) microplastics can be found in a large fraction of aggregates in scenarios with different average diameter of the mixture and number density ratios between microplastic and biogenic particles, (ii) microplastic-containing aggregates will sink to the deeper ocean layers particularly in situations where the biogenic particles are larger and/or of similar size than microplastics, and (iii) the Stokes numbers of aggregates tend not to be significantly different from the Stokes numbers of the initial individual microplastic and biogenic particles. In addition, by examining the collision mechanisms, a model for the collision rate that reproduces the computational results is proposed.

A general Lagrangian tracking methodology for riverine flow and transport

AbstractThis article presents a new public domain tool for generalized Lagrangian particle tracking in rivers. The approach can be applied with a variety of two‐ and three‐dimensional flow solvers. Particle advection by the flow is incorporated using flow fields from the chosen solver assuming particles follow the Reynolds‐averaged flow, although some other simple passive and active particle behaviors are also treated. Turbulence effects are treated using a random walk algorithm with spatial step lengths randomly chosen from Gaussian distributions characterized by the diffusivity from the flow solver. Our work extends this concept to a general framework that is solver and coordinate system independent to allow easy comparisons between differing flow treatments. To better treat problems where detailed information is required in specific regions, the approach includes novel cloning and colligation algorithms which enhance local resolution at modest computational expense. We also provide tools for computing local concentrations and total exposure over a user‐specified time interval. Several examples of predictions are provided to illustrate applications of the technique, including examination of the role of curvature‐driven secondary flows, storage in lateral separation eddies, treatment of larval drift, treatment of fuel spill dispersion, river‐floodplain connections, and sedimentation in floodplain ponds by tie channel connections. We also demonstrate that the model can reproduce analytically derived concentration profiles for simple diffusivities. These examples show that the Lagrangian particle tracking approach and the extensions proposed here are broadly applicable and viable for treating difficult river problems with multiple temporal and spatial scales. The examples also illustrate the utility of the cloning/colligation extensions and show how these can decrease the computational effort required on problems where high local resolution is required. Enhancement of the tools and even broader applicability can be achieved through the inclusion of multiple particle populations and particle–particle interactions.

Improving Numerical Model Predicted Float Trajectories by Deep Learning

AbstractThe Lagrangian tracking approach is often used in numerical modeling (NM) to simulate and predict the movement of marine particles such as plastic, oil spills, and floating wreckage. The uncertainties in NM reduce prediction accuracy as a result of the coarse temporal and spatial resolution, along with waves, winds, and currents. From 29 August to 22 December 2020, the United States Defense Advanced Research Projects Agency's Ocean of Things program deployed 422 floating drifters in the Gulf of Mexico, providing an opportunity of using the observed trajectories as ground truth to train Artificial Intelligence (AI) models to correct NM float trajectory predictions. A Regional Ocean Model System (ROMS) and AI Hybrid model was developed to implement AI to correct the ROMS‐predicted 1‐day float trajectories. The AI model is built on a convolutional neural network and Gated Recurrent Unit. The results of the ROMS‐AI Hybrid model show that 82.0% of the trajectory predictions were improved at the 24 hr, with the corresponding overall mean separation error decreasing by 11.82 km, from 20.56 to 8.74 km, which is a 57% improvement, and the error growth rate decreasing from 5.06 km per 6 hr to 1.95 km per 6 hr. The evident improvement indicates that the ROMS‐AI Hybrid model can correct the ROMS simulation to improve the 1‐day prediction of the float trajectories and shows great potential to predict the cluster of the floats.

Implementation and verification of a Quasi-Eulerian-Eulerian-IATE model for the high-efficient prediction of polydispersed bubbly flows in a continuous casting mold

We implement a new gas–liquid two phase model for the high-efficient prediction of polydispersed bubbly flows in a continuous casting mold. This model shares similarity with the Euler–Lagrange (E-L) method, in which the gas velocity is updated by bubble Lagrangian tracking, and with coupling the phase transport equation in Euler-Euler (E-E) method, thus, it is called the Quasi-Eulerian-Eulerian-IATE (Q-E-E-IATE) model. The local mean bubble size is obtained from solving the interfacial area transport equation (IATE). Various interfacial forces including drag force, lift force, virtual mass force, and turbulent dispersion force are incorporated in this model. This model is verified against published experimental data. Good agreement of gas volume fraction, flow field and bubble size distribution are obtained by adding the virtual mass force and adopting optimized IATE constants. The computational cost of the Q-E-E-IATE model is much lower compared to that of the traditional E-L and E-E models.

Novel streak-resolving algorithm for particle streak velocimetry

In this paper, a novel streak-resolving algorithm is proposed for particle streak velocimetry (PSV) to resolve velocity fields for a single image frame with multiple particle streaks. A model streak function, which was based on the temporal integral of the particle image intensity moving along its trajectory during the exposure period, was approximated using a multivariable least-square fit procedure to reconstruct the streak information and the corresponding particle trajectory. Lagrangian tracking was achieved, and the velocities were evaluated by differentiating the resolved particle trajectory with respect to time. Two types of flows, accelerating parallel flow and the rotational flow of Hill’s vortex, were used to generate synthetic streaks for the performance tests. Three types of relative error were defined and used to evaluate the performance of the algorithm in terms of statistical mean and standard deviation (SD) errors. The accuracy of the fitted streak parameters, such as particle image intensity and diameter, were also evaluated and compared. The results reveal that the error and SD were low if the image noise is below 1.0%; for noise levels of 5.0%, the error was up to 10% with an SD of up to 12%. The error and SD of the particle image intensity and particle image diameter for both flow types were also 0%–7% for clean and up to 12% for noisy images. The processing results for experimental streak images of flow past a cylinder reveal that these images can be resolved using the proposed algorithm with a residual mean error of 4.38 and an SD of 9.48. These results suggest that the proposed novel approach can be used to resolve velocity fields with only a single image frame and without expensive hardware for high-speed imaging and thus is suitable for diverse applications.

Investigation Of Universal Small-Scale Structures In Turbulence Using Shake-The-Box Lagrangian Particle Tracking And FlowFit

A characteristic property of turbulent flows is the presence of a universal small-scale structure consisting of a shear layer separated by two stretched vortices. This pattern becomes visible by averaging the velocity sampled in the eigenframe of the local strain rate tensor. In this contribution, the structure is detected and tracked over time to investigate its formation and decay. For this purpose, experimental data of a von Kármán flow at Re_λ = 370 is used, which is analyzed with Shake-The-Box (STB) Lagrangian Particle Tracking (LPT) and the data assimilation method FlowFit. The universal structure is characterized by the time-resolved mean distribution of dissipation and pressure in the strain rate eigenframe. Using the average power balance terms along all particle trajectories passing through the direct vicinity of conditioned high-dissipation (> 7.5 < ε >) and enstrophy (> 7.5 < νω^2>) events during the time-span from -4 τ_η < t < 4 τ_η the Lagrangian energy transport mechanism through such intermittent events can be discovered, at least in a mean sense. It is shown how the impact of the particles in a high dissipative event leads to a part of the energy being converted into heat and another part into rotation in a time period of approximately 2τ_η . This finding is consistent with the existence of the universal structure. Thus, a connection of Eulerian universal structures with their underlying energy exchange processes is proposed. Furthermore, instantaneous high dissipative events and the Lagrangian tracks that constitute them are shown and related to the statistical results.

Online Event-Based Insights into Unsteady Flows with TrackAER

We present a novel event-based quantitative flow visualization system, TrackAER, capable of continuously reconstructing, rendering and recording particle tracks in large test volumes and without limitations to the measurement duration. Multiple event-based cameras are synchronized and calibrated to produce independent and asynchronous, yet temporally co-registered data streams of flow tracers. Subsequently, these data streams are merged into time-resolved 3D particle tracks using photogrammetric techniques. Due to the operating principle of event cameras, the flow scenery is reduced to moving objects only, which effectively compresses the data stream at the camera source. In combination with an efficient data processing pipeline, the measurement system operates online. That is, the investigated flow field is reconstructed and rendered in an interactive 3D viewer without noticeable time lag. The data processing approach follows a “per-event” paradigm and is achieved in real-time, enabling the immediate observation and analysis of both, transient and long duration flow features. Specific issues resulting from event-based, frame-free processing are discussed as well as the advantages and limitations of event cameras. Exemplary results of two different test cases are provided to demonstrate the utility of the TrackAER system in- and outside a wind tunnel, where Lagrangian particle track information is displayed in a virtual scene together with extracted quantitative information such as local flow velocities.

Heat transfer and mixing enhancement by Poiseuille-Taylor-Couette flow between two rotating elliptically-deformed annular tubes

Multifunctional heat exchangers (HEX) are very important devices which are used in many industrial applications (aerospace, aeronautics, automobile, process and chemical engineering, etc). Improving their designs for an optimal overall performance is still a wide window for both research and development. In the present contribution, a new HEX design is proposed as two concentric elliptically-deformed tubes of complex geometry. Employing advanced computational fluid dynamics (CFD), we show how a combined Poiseuille-Taylor-Couette (PTC) analogous flow between two rotating concentric elliptically-deformed annular tubes, can efficiently enhance heat and mass transfer at low to medium Reynolds numbers (Re≤488). Furthermore, we illustrate how chaotic advection can be controlled by regulating the local flow inertia and rotational forces imposed by a combined flow between: i- Poiseuille flow, and ii- Taylor-Couette analogous flow that is generated by interchanging the clockwise/anticlockwise rotation of the inner and outer walls. Results are presented and discussed using Lagrangian tracking and Poincaré sections techniques that describe the different underlying physical phenomena of mixing and heat transfer.

Flow residence time in intracranial aneurysms evaluated by in vitro 4D flow MRI

The process of an intracranial aneurysm development, growth, and rupture is multifaceted and complex. In addition, clinical observations have identified the potential of thrombus formation within such aneurysms. While the underlying mechanism is not fully understood, the thrombi represent a potential risk factor for ischemic stroke. Emerging studies indicate that blood residence time (RT) is a promising hemodynamic metric associated with the aneurysm rupture and formation of intra-aneurysmal thrombi. Here, we present a methodology to experimentally evaluate both trajectory-wise and local RT based on magnetic resonance imaging (MRI) velocimetry, and apply it to in vitro flow measurements in scaled-up replicas of 9 patient-specific intracranial aneurysms. Lagrangian tracks of massless tracers are integrated from the velocity fields and averaged to return the mean RT in the aneurysm sac. This is found to be closely approximated by a simple time scale based on the sac diameter and space–time average of the aneurysmal fluid velocity. The mean RT is also correlated with the inflow time scale at the parent artery. These results also provide a basis for the estimation of RT when high-resolution hemodynamic maps are not available. With the continuous increase in accuracy and resolution enabled by progress in MRI technology, the methodology described here may in the future be applicable to in vivo data.

Run-to-Tumble Variability Controls the Surface Residence Times of E. coli Bacteria.

Motile bacteria are known to accumulate at surfaces, eventually leading to changes in bacterial motility and biofilm formation. We use a novel two-color, three-dimensional Lagrangian tracking technique to follow simultaneously the body and the flagella of a wild-type Escherichia coli. We observe long surface residence times and surface escape corresponding mostly to immediately antecedent tumbling. A motility model accounting for a large behavioral variability in run-time duration reproduces all experimental findings and gives new insights into surface trapping efficiency.

The importance of continental evaporation for precipitation in Colombia: A baseline combining observations from stable isotopes and modelling moisture trajectories

AbstractThe hydroclimatology of Northern South America responds to the coupling between the Pacific and Atlantic oceans, the Amazon–Andes interactions, and the orographic barrier of the regional Andes. The relative contributions of oceanic and terrestrial moisture sources have been mostly evaluated in modelling studies, with limited observational data for validation. We combine observations from stable isotopes in precipitation and output from the Lagrangian moisture trajectory tracking model FLEXPART to characterize and contrast the relative contribution of oceanic (from the Atlantic and the Pacific) and terrestrial (from different regions in the continent) moisture sources to mean monthly precipitation in the Andes and Caribbean regions of Colombia. Our results indicate that most moisture becoming rain in the region has an atmospheric residence time that deviates from commonly assumed 10 days. These residence times vary between source and sink regions from 1 day in the case of recycling to more than 10 days in Andean precipitation originating in the Atlantic Ocean. Common integration times for both regions from all sources are commonly in the order of three to 7 days. Most precipitation in the region comes from terrestrial sources including moisture recycling from the same region (>30% for all months), the Orinoco River basin (up to 28% in April), and the northern Amazon basin (up to 17% in June, July, and August); followed by individually considered oceanic sources including the Tropical South Pacific (up to 30% monthly in October, November and December) and Tropical North Atlantic (up to 30% monthly for January). The fact that a significant proportion of rainfall is recycled highlights that water availability in the Andean and Caribbean regions of Colombia could potentially be altered by current widespread and pervasive changes in vegetation cover. More generally, our results highlight the need to assess the hydrological consequences of land cover change in South America, particularly in a country like Colombia where water, food, and energy security all depend directly on precipitation.

Hydrodynamic connectivity and dispersal patterns of a transboundary species (Pagellus bogaraveo) in the Strait of Gibraltar and adjacent basins

AbstractThe blackspot seabream (Pagellus bogaraveo) is a benthopelagic fish species highly appreciated by consumers and an important target of the Spanish and Moroccan fisheries in the transcontinental waters of the Strait of Gibraltar area. It is also one of the most exploited resources of the region, which has led to a situation of overexploitation and a notable drop of catches. To gain insight into the sustainability of this resource and certain patterns of the spatial adaptation of the species, a high‐resolution circulation model coupled to a Lagrangian tracking module has been employed to investigate the dispersal pathways of blackspot seabream, using eggs and larvae (early‐life‐stages, ELS) as purely passive particles advected by currents. Several spawning scenarios consisting of different spatial (depths and sites) and temporal (tidal phase and strength) initial conditions have been analyzed to identify the most likely pathways of ELS dispersion. Eastward transport by the Atlantic Jet exiting the Strait of Gibraltar is the most influencing process in that dispersion. Regarding temporal fluctuations, fortnightly tidal modulation is the prevailing factor to determine the horizontal paths of the ELS, spring tides being the cause of the greatest scattering of propagules. Spawning depth in the Strait of Gibraltar is a critical condition, as revealed by the model sensitivity tests. Potential implications of the results of the study to improve the assessment and management of this species are discussed.

Fish damage assessment during the passage through traditional and fish-friendly axial-flow pumps with Lagrangian tracking approach

A large number of fish are prone to death during the passage through pumping stations according to the monitoring data, especially when the axial-flow pumps are equipped. This study comprises the assessment of fish damage for traditional axial-flow pump and the redesigned so-call fish-friendly pump. The Lagrangian tracking approach combined with computational fluid dynamics that takes the fish profile and contact force into account is used to shed light on the fish motion behaviors. The three most important mechanisms for fish injury (i.e. the strike of blade leading edge, pressure reduction and shear force) are discussed. Results show that the fish-friendly pump with reduced number of blades leads to sharp drop of strike probability and its spiral-shaped blade leading edges effectively alleviate the impact force. Pressure reduction and shear force are demonstrated to be severer in the domain of rotating impeller compared with other components, and numerically proven to unlikely pose a threat to fish survival at design condition. The present study offers the evaluation framework of fish damage in axial-flow pumping stations which can be applied to other aquatic organism, and on the other hand points to optimization design of pump to achieve the goal of ecological protection.

Structure of the ethanol spray flame under conventional and MILD conditions

A numerical examination is carried out on the experimental MILD turbulent spray burner of Delft Spray in Hot Co-flow, DSHC. The RANS approach is combined with the Lagrangian tracking of droplets for modeling the pressure-swirl atomizer. The EDC combustion model is employed, to take into account detailed chemical mechanisms. Predictions show that the structure of the triple-flame of liquid fuel in the atmospheric condition is different from the conventional gaseous triple-flames. Furthermore, the structure of the MILD spray flame is compared to the non-MILD spray flame. The flame index shows that the triple-flame structure in the conventional spray flame that consists of two outer and middle diffusion branches, and a premixed inner branch converts to a double-flame structure under MILD condition, including an outer diffusion and a premixed inner branch. In another step, sensitivity analysis relative to the temperature, and oxygen concentration of the co-flow stream is performed independently, which was not possible in the experiment. The parameter of ignition delay time is used for the selection of parametric study cases. Moderate preheating could lead to deviation from the MILD combustion regime, while high preheating is beneficial. NO pollutant generation shows more sensitivity to dilution rather than preheating in MILD spray flame. This study showed that increasing or decreasing each of the temperature and oxygen concentration doesn’t improve all the effective aspects toward achieving the MILD condition. So, the effective parameters should be changed according to a specific and more precise goal.

Drought self-propagation in drylands due to land-atmosphere feedbacks.

Reduced evaporation due to dry soils can affect the land surface energy balance, with implications for local and downwind precipitation. When evaporation is constrained by soil moisture, the atmospheric supply of water is depleted, and this deficit may propagate in time and space. This mechanism could theoretically result in the self-propagation of droughts, but the extent to which this process occurs is unknown. Here we isolate the influence of soil moisture drought on downwind precipitation using Lagrangian moisture tracking constrained by observations from the 40 largest recent droughts worldwide. We show that dryland droughts are particularly prone to self-propagating, because evaporation tends to respond strongly to enhanced soil water stress. In drylands precipitation can decline by more than 15% due to upwind drought in during a single event, and up to 30% during individual months. In light of projected widespread reductions in water availability, this feedback may further exacerbate future droughts.

Effect of electrostatic forces on the dispersion of like-charged solid particles transported by homogeneous isotropic turbulence

The effect of electrostatic forces on the dispersion of small like-charged inertial particles transported by a homogeneous isotropic turbulent flow is analysed by means of direct numerical simulations coupled with the Lagrangian tracking of charged particles. The results show that particle dispersion decreases for increasing charge. Since turbulent particle dispersion is related to the intensity of particle agitation and to the Lagrangian particle integral time scale, we analyse the effects of electrostatic forces on these two quantities. Particle agitation decreases for increasing particle charge. In fact, particle kinetic energy is not directly modified by electrostatic forces, which are conservative, it is rather the particle entrainment by fluid turbulence that is modified. To support this claim, one shows that the fluid–particle velocity covariance is destructed by electrostatic forces, a destruction can be predicted by drawing an analogy between inter-particle collisions and Coulomb collisions. As expected, electrostatic forces decorrelate particle velocities leading to a decrease of the Lagrangian particle integral time scale. Finally, one shows that the analogy with inter-particle collisions allows us to predict the reduction of particle dispersion.

Evaluation of stent effect and thrombosis generation with different blood rheology on an intracranial aneurysm by the Lattice Boltzmann method

Treatment of intracranial aneurysms with flow-diverting stents prevents rupture by reducing blood flow and creating thrombosis within the aneurysm. This paper aims to assess the hemodynamic effect of placing stents with different struts (0, 3, 5, 7 struts) on intracranial aneurysms and to propose a simple prediction model of thrombosis zone without any further computational cost. Lattice Boltzmann method with different rheological models (Newtonian, Carreau-Yasuda, KL) of blood are used to study the hemodynamic effect of flow-diverting stents in the aneurysm. Pulsatile flow boundary conditions were applied in the inlet of the artery. The average Reynolds number was resulting Re=111. The Lagrangian tracking of the particle was developed to assess the intra-aneurysmal blood stagnation. To predict the probable thrombose zone induced by flow-diverting stents, the shear rate threshold is utilized to determine the nodes of fluid to clot. The results show that the flow patterns into the aneurysmal sac develop a vortex, decreasing after stent placement until disappearance for the stent with seven struts (porosity 71.4%). Velocity, shear rate, shear stress, trajectory, path length, and occlusion rate are compared before and after stent placement. These parameters decrease inversely with the porosity of the stent. The three models yield a closes result of the (velocity, shear rate, occlusion rate). Tracking the fluid-particle trajectory shows that the length of the particle paths decreases with the number of struts causing fluid to slow down and increase, consequently, the residence time into the sac. The flow-diverting stents placement cause the reduction of dynamic flow within aneurysm. The reduction effect is almost the same below five struts (80% of porosity). The results show that, if our objective is restricted to estimating the hemodynamic effect, measured by (velocity, shear rate, occlusion rate), the differences between rheological behavior models are, practically, not significant, and the models can be used indifferently.

Nonuniform particle distribution and interference between removal mechanisms during unsteady aerosol deposition from a rising spherical bubble

ABSTRACT Most of the practical computer models available today on aerosol pool scrubbing are built on the basis of fundamental assumptions introduced by Fuchs for his model published in 1955 (in Russian). The primary assumptions are that particle concentration in the bubble can be regarded as uniform and that particle removal mechanisms can be regarded as mutually independent. The present paper shows that these assumptions can cause considerable under- or overprediction of removal rates when applied to particles with radii in the submicrometer range. This size range, known to be where removal mechanisms are generally inefficient, is of particular interest in pool scrubbing study. The present paper, while not being the first to point out the problems with Fuchs’s assumptions, provides a comprehensive description on how the assumptions fail in the submictometer range based on comparisons of Fuchs model predictions against Lagrangian tracking simulations. The simulations, performed for particles of 0.1 to 1.0 m in radius, advected by circulating gas flow in a spherical bubble rising in a water pool, show interference between inertial migration and Brownian diffusion of particles through the development of nonuniform particle concentration profile.