Lagrangian Particle Research Articles

Dynamics of the 1873 CE “Breccia De Fiore” phreatic eruption at Vulcano (Aeolian Islands, Italy) through historical chronicles, physical volcanology, and numerical modelling

Phreatic events may represent precursors of magmatic eruptions or occur independently as single or multiple episodes at volcanoes with hydrothermal systems. We examine the Breccia De Fiore deposit from the prolonged phreatic activity during September–October 1873 at the La Fossa cone of Vulcano (Aeolian Islands, Italy). By integrating data from historical chronicles, stratigraphy, sedimentology, physical analyses, and 3D numerical simulations, we investigate eruption dynamics. The sedimentological characteristics of the deposits, asymmetrically dispersed along the north-western flank of the cone, are interpreted as the simultaneous emplacement of pyroclastic density currents and ballistic projectiles. Numerical simulations model the eruptive mixture as an Eulerian gas-particle fluid coupled with Lagrangian ballistic particles. Results suggest the deposit originated from multiple, shallow, low-magnitude explosions (< 5 × 104 m3 cumulative volume). The deposit dispersal is well reproduced by simulating explosions from an inclined vent, driven by pressure build-up (up to 5 MPa) at shallow depths (< 150 m) within the hydrothermal system. This study helps constrain critical parameters of phreatic scenarios at La Fossa volcano, including erupted mass and specific energy, emphasising the hazards posed by such small events and the crucial need for improving hazard assessment, especially given the close presence of populated, touristic sites.

Riverine substance transport dynamics in a semi-enclosed inland sea

Given the considerable hydrodynamic and ecological implications associated with riverine substances in estuaries, a comprehensive investigation on their fates, pathways, and driving mechanisms is imperative. Consequently, observed drifters were deployed in the Bohai Sea in November 2019, revealing a primary hydrodynamic pattern. To complement the observed trajectories, an unstructured-grid-based particle-tracking model was implemented for the Bohai Sea to delineate the riverine particle transport dynamics during ice-free months (April to November) in 2019. The Lagrangian particle trajectories from riverine substances showed distinct spatial and temporal characteristics. Particles from the Yellow River reached the Central Basin in July, while those from the Hai and Liao Rivers remained localized. Particles from the Luan River travelled to the Central Basin and Bohai Bay regions. Winds significantly alter the spatial scales of particle-influenced area: southerly winds transport particles offshore from the Yellow River, northerly winds move particles from the Hai and Liao Rivers, and both southerly and westerly winds aid in moving particles offshore from the Luan River. While river discharge influences the size of these area, their overall spatial distribution patterns remained mostly consistent regardless of the presence or absence of river discharge. Moreover, momentum analysis confirmed that wind-induced Ekman transport strengthens the coastal-shelf connection, dispersing riverine substances from the Yellow and Luan Rivers away from the coast. In contrast, horizontal advection and the dominance of viscous force override Ekman transport, reducing the coastal-shelf connection in the Bohai and Liaodong Bays.

Simulating the ENSO impact on the distribution and fate of floating litter particles in the Northern South China Sea

The Pearl River delivers a large amount of plastic waste to the Pearl River Estuary (PRE) and adjacent Northern South China Sea (NSCS) region each year. However, the transport of floating litter after release is difficult to predict due to the complex hydrodynamic conditions caused by the climate variability. A regional ocean circulation model coupled with a Lagrangian particle tracking model is utilized in this study to simulate the distribution and fate of floating litter particles in the Pearl River Estuary (PRE) and Northern South China Sea (NSCS) under the influence of El Niño - Southern Oscillation (ENSO) event. Simulations are conducted during all four seasons (spring, summer, fall, and winter) in typical El Niño, La Niña, and ENSO-neutral year. The model reveals that most floating litter remains within Lingding Bay before being transported westward by the counterclockwise circulation over the NSCS and arriving at the Qiongzhou Strait. After crossing the Strait, the debris is carried by the counterclockwise circulation of the Beibu Gulf, and eventually arriving at the coasts of Vietnam and Laos. The ENSO warm (El Niño) and cold (La Niña) phases disrupt circulation patterns and modulate the amount of Pearl River runoff, thereby altering the transport pathways and grounding probabilities of floating litter. During La Niña years, floating litter particles spread over a wider area, travel longer distances, and have lower beaching probabilities. Conversely, during El Niño year, floating litter particles tend to remain within Lingding Bay for longer durations, with some debris entrained towards the Hong Kong region. This study underscores the impact of climate mode of variability in influencing the litter sources, fate and transport and accumulation at estuarine-coastal oceans, which will provide critical scientific insights for plastic pollution management in the PRE - NSCS region, which is a newly identified hotspot for floating litter and microplastic pollution in global oceans.

A Lagrangian particle model for one-dimensional transient pipe flow with moving boundary

For simulating fluid transients in pipelines with moving water-air interface, a one-dimensional Lagrangian particle model with second-order accuracy in both space and time is proposed. In this model, the meshless smoothed particle hydrodynamics (SPH) is used to approximate the spatial derivatives in the waterhammer equations, and the symplectic leap frog scheme is used for time integration. The nonlinear convective terms – which are mostly neglected in classical water hammer – are taken into account. The details of the Lagrangian particle method, boundary condition treatment and artificial viscosity for remedy of numerical oscillations due to shocks are presented. Two typical cases including transient flow with entrapped air pocket and rapid pipe filling are simulated and the results are validated against available experimental and numerical solutions, which has wide applications for flow simulation in drainage networks. To test the shock capturing ability of the developed model, the classical water hammer problem is also simulated and good agreement with the theoretical solution is obtained. It is shown that the proposed Lagrangian particle model is capable of solving waterhammer equations with moving boundaries and that it has high potential for multiphase transient flows.

Modeling the advective supply of Calanus finmarchicus to Stellwagen Bank as an indicator of sand lance foraging habitat, and the climate vulnerability of a National Marine Sanctuary

The northern sand lance (Ammodytes dubius), a key species in the food web supporting the Stellwagen Bank National Marine Sanctuary (SBNMS), feeds primarily on the lipid-rich copepod Calanus finmarchicus. Climate change poses a significant threat to this dynamic, as C. finmarchicus populations are at the southern edge of their subarctic distribution and are vulnerable to warming waters and changing oceanographic conditions. Declines in the advective supply of C. finmarchicus to Stellwagen Bank could adversely affect sand lance populations and, consequently, the ecological and economic resources that depend on them. To quantify the connectivity between SBNMS and potential sources of C. finmarchicus, we used the Finite-Volume Community Ocean Model (FVCOM) coupled with Lagrangian particle tracking over the years 1978 to 2016. Numerical experiments revealed that Stellwagen Bank is highly connected to upstream areas in the Maine Coastal Current (MCC), where existing time series monitoring stations observe C. finmarchicus populations. The connectivity exhibited strong seasonal patterns, with peak connectivity occurring during spring and early summer, aligning with the sand lance feeding period on C. finmarchicus. We found significant interannual variability, influenced by changes in the strength of the MCC and circulation patterns in the western Gulf of Maine. Years with stronger MCC flow showed higher connectivity and a greater potential supply of C. finmarchicus particles to Stellwagen Bank. Conversely, periods of reduced flow corresponded with decreased connectivity, potentially limiting the availability of C. finmarchicus to sand lance populations. Meanwhile, observations from drifters and buoys since 2001 have documented decreases in MCC current speed which has been linked to a climate driven strengthening of southwesterly winds. These findings underscore the importance of pelagic habitat connectivity in assessing the climate vulnerability of marine protected areas (MPAs) like SBNMS. Furthermore, monitoring C. finmarchicus populations at upstream time series stations can provide information on downstream foraging habitat in MPAs, and potentially in other vulnerable areas of ecological and socioeconomic interest. By incorporating these indicators of connectivity and upstream C. finmarchicus population abundance into decision support tools, Sanctuary managers and stakeholders can make informed decisions to mitigate potential climate impacts.

Dynamic wall shear stress measurement using event-based 3d particle tracking

We describe the implementation of a 3d Lagrangian particle tracking (LPT) system based on event-based vision (EBV) and demonstrate its application for the near-wall characterization of a turbulent boundary layer (TBL) in air. The viscous sublayer of the TBL is illuminated by a thin light sheet that grazes the surface of a thin glass window inserted into the wind tunnel wall. The data simultaneously captured by three synchronized event cameras are used to reconstruct the 3d particle tracks within 400μm of the wall on a field of view of 12.0mm×7.5mm. The velocity and position of particles within the viscous sublayer permit the estimation of the local vector of the unsteady wall shear stress (WSS) under the assumption of linearity between particle velocity and WSS. Thereby, time-evolving maps of the unsteady WSS and higher-order statistics are obtained that are in agreement with DNS data at matching Reynolds number. Near-wall particle acceleration provides the rate of change of the WSS which exhibits fully symmetric log-normal superstatistics. Two-point correlations of the randomly spaced WSS data are obtained by a bin-averaging approach and reveal information on the spacing of near-wall streaks. The employed compact EBV hardware coupled with suited LPT tracking algorithms provides data quality on par with currently used, considerably more expensive, high-speed framing cameras.

Clustering of buoyant tracer in quasi-geostrophic coherent structures

We have investigated the dynamics of floating tracer in an idealised turbulent quasi-geostrophic ocean by advecting Lagrangian particles in a high-resolution velocity field enhanced by the potential flow associated with vortex stretching. At first order in the Rossby number expansion, this component of the ageostrophic circulation can be derived through a diagnostic equation in terms of the geostrophic velocities. Borrowing methods from the theory of Lagrangian coherent structures, we identify coherent material loops around strong vortex cores using the Lagrangian averaged vorticity deviation (LAVD). Building on studies of clustering in kinematic, stochastic velocity fields, we utilise methods from statistical topography to show that the coherent vortices dominate the distribution of extreme values of the concentration field. We find that the presence of clusters and voids in a coherent vortex depends on more than just the sense of rotation, but also on the full evolution of the vorticity over its lifecycle. We identify the mechanism behind the cluster formation that respects the symmetries of the quasi-geostrophic equations but can be expected to hold robustly in more complicated regimes, due to the simple physical description. The association of cluster formation with vortex stretching implies that LAVD is a particularly relevant metric for floating tracer dynamics. The detection of intense clustering also has implications for reaction rates between ocean-borne flotsam, meaning that our results are relevant to understanding the general risk of floating microplastics and marine biological populations.

Efficiency and scalability of fully-resolved fluid-particle simulations on heterogeneous CPU-GPU architectures

Current supercomputers often have a heterogeneous architecture using both conventional Central Processing Units (CPUs) and Graphics Processing Units (GPUs). At the same time, numerical simulation tasks frequently involve multiphysics scenarios whose components run on different hardware due to multiple reasons, e.g., architectural requirements, pragmatism, etc. This leads naturally to a software design where different simulation modules are mapped to different subsystems of the heterogeneous architecture. We present a detailed performance analysis for such a hybrid four-way coupled simulation of a fully resolved particle-laden flow. The Eulerian representation of the flow utilizes GPUs, while the Lagrangian model for the particles runs on conventional CPUs. Two characteristic model situations involving dense and dilute particle systems are used as benchmark scenarios. First, a roofline model is employed to predict the node level performance and to show that the lattice-Boltzmann-based Eulerian fluid simulation reaches very good performance on a single GPU. Furthermore, the GPU-GPU communication for a large-scale Eulerian flow simulation results in only moderate slowdowns. This is due to the efficiency of the CUDA-aware MPI communication, combined with the use of communication hiding techniques. On 1024 A100 GPUs, an overall parallel efficiency of up to 71% is achieved. While the flow simulation has good performance characteristics, the integration of the stiff Lagrangian particle system requires frequent CPU-CPU communications that can become a bottleneck, especially when simulating the dense particle system. Additionally, special attention is paid to the CPU-GPU communication overhead since this is essential for coupling the particles to the flow simulation. However, thanks to our problem-aware co-partitioning, the CPU-GPU communication overhead is found to be negligible. As a lesson learned from this development, four criteria are postulated that a hybrid implementation must meet for the efficient use of heterogeneous supercomputers.

Mixing by internal gravity waves in stars: assessing numerical simulations against theory

ABSTRACT Here we present a study of radial chemical mixing in non-rotating massive main-sequence stars driven by internal gravity waves (IGWs), based on multidimensional hydrodynamical simulations with the fully compressible code MUSIC. We examine two proposed mechanisms of material mixing in stars by IGWs that are commonly quoted, relating to thermal diffusion and sub-wavelength shearing. Thermal diffusion provides a non-restorative effect to the waves, leaving material displaced from its previous equilibrium, while shearing arising within the waves drives weak localized flows, mixing the fluid there. Using IGW spectra from the simulations, we evaluate theoretical predictions of mixing rates due to these mechanisms. We show, for $20\, \mathrm{M}_\odot$ main-sequence stars, that neither of these mechanisms are likely to create mixing sufficient to correct inaccuracies in current stellar evolution models. Furthermore, we compare these predictions to results obtained from Lagrangian tracer particles, following a method recently used for global simulations of stellar interiors to measure mixing by IGWs in their radiative zones. We demonstrate that tracer particle methods face significant numerical challenges in measuring the small diffusion coefficients predicted by the aforementioned theories, for which they are prone to yielding artificially enhanced coefficients. Diffusion coefficients based on such methods are currently used with stellar evolution codes for asteroseismic studies, but should be viewed with caution. Finally, in a case where tracer particles do not suffer from numerical artefacts, we suggest that a diffusion model is not suitable for time-scales typically considered by 2D numerical simulations.

Efficient Method for Improving Fully Implicit Scheme in Smoothed Particle Hydrodynamics for Highly Viscous and Non‐Newtonian Polymer Flow

ABSTRACTSmoothed particle hydrodynamics (SPH), a fully Lagrangian particle method, has been widely used in various applications, such as the simulation of incompressible flow with a free surface. For highly viscous flow, which typically appears in polymer processing, a fully implicit scheme, which implicitly treats both the predictor and corrector procedures of the projection method in the SPH framework, is efficient and numerically stable. This study proposes a simple and efficient fully implicit scheme that improves predictive accuracy for highly viscous flow. The proposed scheme utilizes a recently developed scheme for highly viscous flow that performs the pressure calculation before the viscosity diffusion calculation, unlike the conventional projection method. This study further improves the viscosity diffusion calculation by considering a viscous diffusion term that is usually ignored due to the continuity equation. Including this term enables us to correctly perform calculations for non‐Newtonian flows. The increase in the computational cost that results from the inclusion of the term is alleviated by introducing a two‐step method for calculating the viscous diffusion terms. The developed scheme is applied to injection molding of a polymer melt between two parallel plates. The results show that the proposed two‐step implicit scheme reproduces the fountain flow behavior near the advancing front. In addition, a three‐dimensional molding simulation of a plate with a hole shows a significant improvement in the prediction of the filling pattern in the mold.

UV processing of icy pebbles in the outer parts of VSI-turbulent disks

Icy dust particles emerge in star-forming clouds and are subsequently incorporated in protoplanetary disks, where they coagulate into larger pebbles up to millimeter in size. In the disk midplane, ices are shielded from UV radiation, but moderate levels of disk turbulence can lift small particles to the disk surface, where they can be altered, or destroyed. Nevertheless, studies of comets and meteorites generally find that ices at least partly retain their interstellar medium (ISM) composition before being accreted onto these minor bodies. We modeled this process through hydrodynamical simulations with vertical shear instability (VSI) driven turbulence in the outer protoplanetary disk. We used the PLUTO code in a 2.5 D global accretion setup and included Lagrangian dust particles of 0.1 and 1 mm sizes. In a post-processing step, we used the RADMC3D code to generate the local UV radiation field to assess the level of ice processing of pebbles. We find that a small fraction (∼17%) of 100 µm size particles are frequently lifted up to Z/R = 0.2, which can result in the loss of their pristine composition as their residence time in this layer allow effective CO and water photodissociation. The larger 1 mm size particles remain UV-shielded in the disk midplane throughout the dynamical evolution of the disk. Our results indicate that the assembly of icy bodies via the accretion of drifting millimeter-sized icy pebbles can explain the presence of pristine ice from the ISM, even in VSI-turbulent disks. Nevertheless, particles ≤100 µm experience efficient UV processing and may mix with unaltered icy pebbles, resulting in a less ISM-like composition in the midplane.

Vortical waves in a quantum fluid with vector, axial, and helical charges. I. Non-dissipative transport

Due to the spin-orbit coupling, Dirac fermions, submerged in a thermal bath with finite macroscopic vorticity, exhibit a spin polarisation along the direction parallel to the vorticity vector Ω. Due to the symmetries of the Lagrangian for free massless Dirac particles, there are three independent and classically conserved currents corresponding to the vector, axial, and helical charges. The constitutive relations for the charge currents and the stress-energy tensor at thermal equilibrium, derived in the framework of quantum field theory at finite temperature, reveal vorticity-induced contributions that deviate from the perfect fluid form. In this paper, we consider the mode structure of the corresponding hydrodynamical theory and derive collective excitations associated with coherent fluctuations of all three charges. We show that the chirally imbalanced rotating fluid should possess non-reciprocal gapless waves that propagate with different velocities along and opposite to the vorticity vector. We also uncover a strictly unidirectional mode, which we call the axial vortical wave, propagating in the background of the axial charge density. The emergence of this wave can be traced back to earlier studies of vortical chiral fluids in a hydrodynamic approach. We also point out an unexpected instability in the limit of degenerate matter and discuss possible solutions when helicity and axial charge non-conservation are taken into account.

Towards LES of Liquid Jet Atomization Using an Eulerian-Lagrangian Multiscale Approach

AbstractThis study is concerned with Large Eddy Simulation of liquid jet atomization using a two-way coupled Eulerian-Lagrangian multiscale approach. The proposed framework combines Volume-of-Fluid interface capturing with Lagrangian Particle Tracking. The former is used to compute the core jet and large liquid elements in the near-nozzle region, whereas the latter is used to track the large number of small droplets in the dilute downstream region of the spray. The convective and surface tension sub-grid scale terms arising in the context of two-phase flow LES are closed using suitable models, and secondary atomization is considered by employing a modified version of the Taylor Analogy Breakup model. The introduced framework is used to simulate an oil-in-air atomization as well as the Diesel-like Spray A test case of the Engine Combustion Network. Compared to previous studies based on Eulerian-Lagrangian methods, the present work stands out for the high-fidelity numerical approach, the complex test cases and the detailed comparison of the results to experimental data, which indicates a promising performance.

Numerical simulations on effects of turbulence on the size spectrum of sinking particles in ocean surface boundary layer

Sinking particles in the ocean play a crucial role in the climate system by transporting materials, such as carbon, deep into the ocean. The amount of this transport is influenced by the net sinking speed of the particles and the amount of material attached to them, both of which are determined by the size spectrum of the particles. The spectrum is shaped by aggregation and disaggregation processes, which are typically most active in the ocean surface boundary layer (OSBL), where intense turbulent flows can enhance both particle collision (aggregation) and particle fragmentation (disaggregation). This study aims to reveal the mechanism by which turbulence transforms the size spectrum through these competing processes and to determine whether turbulence alters the downward material transport from the OSBL. To achieve this, we performed large-eddy simulations to reproduce wind- and wave-induced turbulent flows, employing a Lagrangian particle model to track passive particles in the flow and simulate their aggregation and disaggregation. The model tracked groups of particles rather than individual ones. The results revealed that the shape of the simulated size spectrum was characterized by two length scales, the compensation radius (characterizing the particle floatability) and the Kolmogorov scale, which define the shear range where the turbulent shear shapes the spectrum, the sinking range where the gravitational sinking of particles shapes the spectrum, and the transition range between them. The findings revealed that turbulence tends to increase the terminal velocity and decrease the specific surface area of sinking particles when turbulent aggregation dominates over disaggregation, and vice versa. Although these results may be influenced by uncertain parameterizations (e.g., disaggregation parameterization), the study demonstrates the effectiveness of the numerical approach in investigating the fundamental processes governing particle sinking in turbulent flows.

Aerodynamic interaction of rain and wind turbine blades: the significance of droplet slowdown and deformation for leading-edge erosion

Abstract. Leading-edge rain erosion is a severe problem in the wind energy community since it leads to blade damage and a reduction in annual energy production by up to a few percent. The impact speed of rain droplets is a key driver of the erosion rate; therefore, its precise computation is essential. This study investigates the aerodynamic interaction of rain droplets and wind turbine blades. Based on findings from the literature and an analysis of the relevant parameter space, it is found that the aerodynamic interaction leads to a reduction in the impact speed. Additionally, the rain droplets deform and break up as they approach the wind turbine blade. An existing Lagrangian particle model, developed for research in aircraft icing, is adapted, extended, and validated for leading-edge rain erosion to study the process in more detail. Results show that the droplet slowdown reduces predicted damage toward the tip of the blade by over 50 %. The model indicates that the aerodynamic blade interaction affects small droplets significantly more than large droplets. Due to this drop-size dependency, the damage accumulation is shifted toward higher-rain-intensity events. Additionally, the droplet impact speed is sensitive to the aerodynamic nose radius of the airfoil. Due to this sensitivity and its drop-size dependency, the slowdown effect provides interesting levers for erosion mitigation via blade design or operational adjustments. To conclude, the aerodynamic interaction between droplet and blade is non-negligible and needs to be taken into account in erosion lifetime models.

Impacts of Urban Heat and Surface Roughness on Landfalling Tropical Cyclone Intensity: A Case Study Based on TC Victor (1997) in Coastal South China

AbstractThis study investigates the impacts of urban‐induced anthropogenic heat (AH) and surface roughness on Tropical Cyclone (TC) Victor (1997) using the Weather Research and Forecasting Model. TC Victor originated in the South China Sea and made landfall over the Greater Bay Area (GBA) megacity. The storm was characterized by slow movement, a weakly organized structure, and a small size. Three parallel experiments were conducted in the following setups: “Nourban,” where urban areas in the GBA were replaced by croplands, “AH0” (“AH300”), in which the diurnal maximum AH was set to 0 (300 W/m2) in urban locations. The urbanization effect during the landfall period results in a notable reduction in both the Power Dissipation Index and Integrated Kinetic Energy of the storm. A Lagrangian particle dispersion model further demonstrates that from 33 to 17 hr prelandfall, the entrainment of AH‐affected warm airflow into the TC's circulation leads to a decrease in both the convective available potential energy and surface latent heat flux in the western quadrant of the TC, thus weakening the cyclone's intensity. Furthermore, from 12 hr prelandfall to 8 hr postlandfall, there is an intense influx of AH‐affected airflow into the TC's primary circulation, resulting in a decrease in relative humidity and a stronger asymmetrical structure, declining the TC intensity. Concurrently, urban surface roughness contributes to a decrease in postlandfall storm intensity through frictional energy dissipation. This study underscores the critical role of AH and urban roughness in modulating TC intensity for storms with specific characteristics, emphasizing the need for deeper insights into urban‐TC dynamics.

An updated Lagrangian particle hydrodynamics (ULPH) implementation of heat conduction model for weakly-compressive fluid

An updated Lagrangian particle hydrodynamics (ULPH) implementation of heat conduction model for weakly-compressive fluid

Four-dimensional flow characteristics of air-entrained turbulent impinging waterjet onto quiescent water surface

This paper presents a time-resolved three-dimensional (4D) flow fields measurement of the continuous phase of a turbulent impinging jet inducing foam formation using the Lagrangian particle tracking velocimetry utilizing the Shake-The-Box algorithm. With the systems equipped with four high-speed cameras, time-series of images of fluid tracer particles were acquired. The Vortex-In-Sharp (VIC#) method was used to reconstruct the Eulerian flow fields of the particle tracks. The impinging jet was characterized as plume-like along the vertical direction with two distinct layers: developing shear and fully developed shear. The streamwise vortex structures of the continuous phase were influenced by the bubble plume motion, and the results showed high amplitude oscillations of the acceleration and deceleration near the jet source resulting in the formation of ring-like vortices, which break down as the jet moves downstream with its momentum dissipated. The flow of the continuous phase of impinging jet was self-similar both at the developed shear layer and the fully developed diffusion layer beneath the water pool and is characterized as homogeneous shear flow with anisotropy turbulence. The classical assumption of self-similarity with Gaussian profiles for continuous phase velocity is verified experimentally. We found that the results show a huge potential of blue energy harvesting from the low frequency (∼2 Hz) dissipating kinetic energy of the turbulent plume-like jet underneath the impinging water surface using triboelectric nanogenerator.

Introducing a simple convex hull method to calibrate diffusion coefficients in Lagrangian particle models

Calibrating Lagrangian particle models (LPMs) is crucial for simulating oil spill trajectories, enabling emergency responses, and mitigating harmful effects on the environment. However, there is a lack of rigorous observation data on oil spill events, especially in water bodies with no serious spills but perceived increasing risk, hampering LPM application. This study utilized trajectory data from three drifters in Lake Erie, collected in 2016, 2018, and 2019. We then proposed a simple and efficient convex hull method to identify the smallest envelope of the simulated particle cloud, covering all drifter trajectories while simultaneously controlling over-diffusion. This approach was employed to calibrate the General NOAA Operational Modeling Environment oil spill model (an LPM) and determine optimal diffusion coefficients. Based on 362 one-day-long drifter trajectory simulation cases, the recommended diffusion coefficient for particle trajectory simulation in Lake Erie was determined to be 14 m2 s−1. The calibrated model demonstrated the ability to effectively capture the movement direction of drifters and control the discrepancy between simulated and observed trajectories. Meanwhile, it underestimated drifter travel distances due to errors in input currents, the primary force driving drifter movement. These results promote LPM application for particle trajectory simulations.

CFD analysis of microscopic particle separation in low-volumetric classifiers: DPM tracking and experimental validation for enhanced efficiency using geometric modification strategy

The increasing demand for advanced air quality management technologies highlights the need for efficient separators capable of classifying microparticles by size. This study introduces a novel approach of geometric modifications to optimize low-volumetric environmental separators through Computational Fluid Dynamics (CFD) simulations. This study investigated micron particle flow behaviour, vortex strength, and separation chamber design using Lagrangian particle tracking to capture the complex particle–fluid interactions. Key geometry modifications included optimizing internal configurations, such as tube arrangements and discharge tube lengths, which resulted in significantly improved separation efficiency. The CFD simulations were validated against experimental data with flow rates ranging from 10 to 20 LPM (Re = 1008, 1512, 2016), demonstrating flow patterns, vorticity, and particle retention. A major contribution of this study is the particle retention efficiency analysis across a wide range of particle sizes. Particles larger than 10 µm were captured with near-perfect efficiency, while capturing finer particles (1–8 µm) proved more challenging, highlighting areas for future improvement. Notably, increasing the number of separation tubes from 3 to 4 and adjusting their heights led to a 10 % increase in particle retention for particle diameters of 10 and 20 µm. Additionally, higher flow rates, especially at 17 LPM (Re = 1714), increased capture rates for medium-sized particles by prolonging residence times through increased turbulence. This research advances micron particle separation technologies through design optimizations, supported by experimental and numerical analysis. The findings have broad implications for improving the performance of environmental separators in industrial applications, and for future developments in air quality management systems.