Lagrangian Particle Tracking Method Research Articles

Modeling of micron-sized aluminum particle combustion in hot gas flow

This paper presents a model for micron-sized aluminum (Al) particle combustion in hot oxidizing environments, forming hollow spheres. The model comprises four sub-models describing the physical and chemical processes during Al combustion: melting of the solid core, ejection of liquid Al droplets from the breaking solid shell, vaporization of liquid droplets, and ignition and establishment of vapor flame surrounding the solid particles. The model is of critical importance when the ambient gas temperature is higher than the melting point of the Al core, Tc,m, but lower than the alumina (Al2O3) shell’s melting point, Ts,m. In the model, the Al core is assumed to be surrounded by a thin, compact alumina shell that blocks the diffusion of oxidizer into the core and prevents surface reactions. The alumina shell’s cracking and liquid Al’s eruption are triggered by thermal expansion and pressure buildup in the liquid core. The splashed liquid Al droplets vaporize quickly and initiate gas-phase reactions, followed by the vaporization of the liquid Al core as the particle temperature Tp increases. Al vapor combustion heat is redistributed to simulate the gaseous flame near the particle. The model is implemented using the Lagrangian particle tracking method and is validated through simulations of micron-sized Al particle combustion in hot gas and comparison with experiments. The results can explain the formation of the sharp-edged holes on hollow aluminum oxide spheres and the ignition behavior observed in the experiments.

Numerical simulation and spray model development of liquid ammonia injection under diesel-engine conditions

Ammonia is regarded as a promising alternative fuel in internal combustion engine for its potential to reduce carbon emissions. Injection process of liquid ammonia will affect air-fuel mixture distribution and therefore combustion efficiency and NOx emissions. However, the experimental studies of liquid ammonia injection under engine conditions are limited, and the key impact factors of spray evolution are still unclear. This study aims to evaluate the applicability of numerical models for liquid ammonia spray, and numerically investigate spray characteristics under diesel-engine conditions (ambient temperature > 800K, ambient pressure > 2 MPa). Large eddy simulation coupled with Lagrangian particle tracking method were conducted, and the results show that the non equilibrium - Frössling phase change model coupled with Schiller-Naumann drag model can provide a good prediction of spray penetration. Liquid penetration increases with ambient pressure decreasing; vapor penetration increases with ambient density decreasing, but insensitive to ambient temperature. Temperature - mixture fraction distribution is sensitive to ambient temperature and superheat degree. Besides, a three-stage 0D model of spray tip penetration under diesel-engine conditions is developed firstly, which can reflect the key impact factors of ammonia spray evolution and provide theoretical support to optimize fuel injection strategy of liquid ammonia-fueled engines.

Study on atomization characteristics of a kerosene jet in a supersonic crossflow

The combustion performance of a scramjet engine is based on a two-phase mixing process of its fuel. To elucidate the mechanism of jet atomization in supersonic airflows, a numerical simulation of liquid jet atomization in a supersonic crossflow is carried out. The Euler method is used to calculate the gas phase, while the Lagrangian particle tracking method is used to calculate the liquid phase. The Reitz wave model is used to simulate the first breakup of the liquid jet, and the Kelvin-Helmholtz/Rayleigh-Taylor hybrid breakup model is used to simulate the second breakup of the droplets. The influence of the liquid/gas momentum flux ratio and the diameter of the jet on the atomization characteristics is discussed. The results show that the penetration depth increases with increasing nozzle diameter and liquid/gas momentum flux ratio. A jet with a larger liquid/gas momentum flux ratio breaks faster, and its Sauter mean diameter is smaller. The Sauter mean diameter of a droplet decreases with decreasing nozzle diameter. At 30 mm downstream of the nozzle, all jets are basically atomized, and the SMD of the jet is around 10 μm. The nozzle diameter has a greater influence on the jet penetration depth than does the liquid/gas momentum flux ratio.

Prediction of the aggregation rate of nanoparticles in porous media in the diffusion-controlled regime.

The fate and aggregation of nanoparticles (NPs) in the subsurface are important due to potentially harmful impacts on the environment and human health. This study aims to investigate the effects of flow velocity, particle size, and particle concentration on the aggregation rate of NPs in a diffusion-limited regime and build an equation to predict the aggregation rate when NPs move in the pore space between randomly packed spheres (including mono-disperse, bi-disperse, and tri-disperse spheres). The flow of 0.2M potassium chloride (KCl) through the random sphere packings was simulated by the lattice Boltzmann method (LBM). The movement and aggregation of cerium oxide (CeO2) particles were then examined by using a Lagrangian particle tracking method based on a force balance approach. This method relied on Newton's second law of motion and took the interaction forces among particles into account. The aggregation rate of NPs was found to depend linearly on time, and the slope of the line was a power function of the particle concentration, the Reynolds (Re) and Schmidt (Sc) numbers. The exponent for the Sc number was triple that of the Re number, which was evidence that the random movement of NPs has a much stronger effect on the rate of diffusion-controlled aggregation than the convection.

On the relative importance of saltation and suspension for aeolian snow mass transport

AbstractSnow transport affects various hydrological processes significantly through reshaping the glacial landscapes. Snow particles that are transported in a turbulent flow are typically classified under the saltation and suspension states based on the inertia of the particles relative to the strength of the turbulence. In this study, snow transport in the turbulent boundary layer was simulated using the large‐eddy simulation with Lagrangian particle tracking method. Contrary to most previous studies in which saltation and suspension are defined by a specified critical height or particle size, hop time ratio Rt and particle Stokes number St were adopted to judge the state of saltating snow particles, and the contributions of pure saltation, modified saltation, short‐ and long‐term suspension particles were quantified appropriately. A threshold value of St≈5 for pure saltation was proposed through the particle trajectory comparison. The results show that the St criterion measures pure saltation particle appropriately but fails to diagnose long‐term suspension particles. Furthermore, although there are hardly any pure saltation particles in natural snow transport, the contribution of modified saltation cannot be neglected in the lowest centimetres of the atmosphere, which may also dominate the overall mass flux at the near surface under larger friction velocities. Rather, considerable short‐ and long‐term suspended particles spread over the entire vertical dimension of the snow cloud, contributing a major proportion of the overall mass flux, even within the saltation layer. Based on this, the suspension layer should be defined as the entire vertical dimension of the particle cloud. The results can improve our understanding of the motion dynamics of transported snow particles and further provide new ideas in modelling this process.

Multiscale modeling of liquid jet breakup in crossflow using an Eulerian/Lagrangian approach

Liquid atomization is a very complex issue, involving multiple length and time scales over several orders of magnitude. To better understand the atomization characteristics of the main injection in a lean premix prevaporize (LPP) combustor, a volume of fluid (VOF)–particle conversion algorithm Lagrangian particle tracking (LPT) coupled approach was proposed to simultaneously reproduce the primary and secondary breakup processes. A VOF model with an adaptive mesh refinement strategy was used to resolve the liquid disintegration on a large scale. The small liquid structures qualified as droplets were transformed into discrete particles based on particle conversion criteria. Next, these particles were tracked using the LPT method to simulate the secondary breakup process. The proposed coupled method used in the Eulerian/Lagrangian framework was validated against liquid jet in crossflow experimental data. The numerical results achieved good agreement with the experimental data. Finally, the proposed method was used to predict the atomization characteristics of the main injection in an LPP combustor under various aerodynamic conditions. Qualitative and quantitative information about liquid deformation and spray characteristics were obtained, which varied depending on the aerodynamic parameters.

Performance assessment of an electrostatic filter-diverter stent cerebrovascular protection device. Is it possible not to use anticoagulants in atrial fibrilation elderly patients?

Stroke is the second leading cause of death worldwide. Nearly two-thirds of strokes are produced by cardioembolisms, and half of cardioembolic strokes are triggered by Atrial Fibrillation (AF), the most common type of arrhythmia. A more recent cause of cardioembolisms is Transcatheter Aortic Valve Replacements (TAVRs), which may onset post-procedural adverse events such as stroke and Silent Brain Infarcts (SBIs), for which no definitive treatment exists, and which will only get worse as TAVRs are implanted in younger and lower risk patients. It is well known that some specific characteristics of elderly patients may lower the safety and efficacy of anticoagulation therapy, making it a real urgency to find alternative therapies. We propose a device consisting of a strut structure placed at the base of the treated artery to model the potential risk of cerebral embolisms caused by dislodged debris of varying sizes. This work analyzes a design based on a patented medical device, intended to block cardioembolisms from entering the cerebrovascular system, with a particular focus on AF, and potentially TAVR patients. The study has been carried out in two stages. Both of them based on computational fluid dynamics (CFD) coupled with Lagrangian particle tracking method. The first stage of the work evaluates a variety of strut thicknesses and inter-strut spacings, contrasting with the device-free baseline geometry. The analysis is carried out by imposing flowrate waveforms characteristic of both healthy and AF patients. Boundary conditions are calibrated to reproduce physiological flowrates and pressures in a patient's aortic arch. In the second stage, the optimal geometric design from the first stage was employed, with the addition of lateral struts to prevent the filtration of particles and electronegatively charged strut surfaces, studying the effect of electrical forces on the clots if they are considered charged. Flowrate boundary conditions were used to emulate both healthy and AF conditions. Results from numerical simulations coming form the first stage indicate that the device blocks particles of sizes larger than the inter-strut spacing. It was found that lateral strut space had the highest impact on efficacy. Based on the results of the second stage, deploying the electronegatively charged device in all three aortic arch arteries, the number of particles entering these arteries was reduced on average by 62.6% and 51.2%, for the healthy and diseased models respectively, matching or surpassing current oral anticoagulant efficacy. In conclusion, the device demonstrated a two-fold mechanism for filtering emboli: while the smallest particles are deflected by electrostatic repulsion, avoiding microembolisms, which could lead to cognitive impairment, the largest ones are mechanically filtered since they cannot fit in between the struts, effectively blocking the full range of particle sizes analyzed in this study. The device presented in this manuscript offers an anticoagulant-free method to prevent stroke and SBIs, imperative given the growing population of AF and elderly patients.

Modeling Edge Flame Propagation for Flame Particle Tracking in the Forced Ignition Process of Turbulent Nonpremixed Jet Flame

ABSTRACT To ensure safe and reliable operation, ignition performance in propulsion and power devices needs to be thoroughly assessed. Reduced order models (ROMs) for ignition have gained increasing attention, given that first-principles models are restricted by immense computational costs that preclude rapid assessment for the design purpose. Currently, flame self-propagation is generally neglected in the ROM descriptions of ignition process and the impact on the flame front dynamics as well as the ignition probability map is not clear for low swirl or jet flames which are of interest for industrial applications. In this study, an empirical model for flame self-propagation is proposed to augment the capability of Lagrangian flame particle tracking method, a ROM model to predict ignition probability based on nonreacting flow field. The model adopts the classic scaling law of turbulent flame speed together with fuel gradient correction and flame self-propagation to mimic the edge flame dynamics during the ignition process. The model performances in terms of flame front dynamics and ignition probability map are quantified in a turbulent nonpremixed methane-air jet flame. Results reveal that only with flame self-propagation, the flame particle tracking can well capture the transient evolution of the leading flame front as observed in experiments. It is found that the predicted ignition probability map agrees well with experimental data with high ignition probability around the vicinity of the stoichiometric region at the downstream axial distance of 6 to 40 times the jet diameter. This study illustrates the importance to account for flame self-propagation to correctly predict ignition probability in jet dominant nonpremixed flames.

Numerical Analysis of a Novel Rotating Piston Blood Pump Based on CFD

Currently, centrifugal and roller pumps are primarily used as ECMO blood pumps, but their high pressure or high shear force may lead to complications such as hemolysis and platelet activation. Thus, a new blood pump structure was designed by improving the rotating piston pump and applying it to the blood pump. The blood pump flow field was simulated using CFD simulation software to ensure that this pump can produce pulsatile blood flow and guarantee good distribution of flow velocity, pressure, and shear stress in the blood pump. The hemolysis value of the pump was calculated using the Lagrangian particle tracking method. The research results demonstrate that this pump has excellent hemodynamic performance and that most of the shear stresses are less than 100 Pa, as well as a small hemolysis index. Furthermore, the pump combines the advantages of pulsatile and non-pulsatile pumps. This newly developed pump is expected to provide a new direction for ECMO blood pump development and provides important evidence for further optimization and performance evaluation of rotating piston blood pumps.

MOVEMENT OF MICROPLASTICS IN THE WASTEWATER DISCHARGED FROM THE ANTARCTIC RESEARCH STATION

As a large number of microplastics (MPs) have been found around the Antarctic research stations, the wastewater from the station is presumed to be a local source of MPs pollution (Waller et al., 2017). In addition, more than half of stations in Antarctica have no adequate sewage treatment systems (Gröndahl et al., 2009). The present study collected MPs in Marian Cove, West Antarctica. In this bay, the King Sejong Station, which is a Korea station, is located, and other research stations are located around. And, we actually found a significant amount of MPs in the seawater and wastewater of the station. So, we assumed that this research station can be a local source in this cove. To investigate how the MPs discharged from the stations are transported and accumulated, it is necessary to understand the movement of MPs. This study investigated the movement of MPs discharged from the research station through numerical simulation to elucidate the transport mechanism of MPs. And, the Lagrangian particle tracking method was coupled with the numerical simulation to track the trajectories of MPs. The present study finally suggested an optimal wastewater discharge method by simulating MPs according to waves, tidal cycles, and discharge locations.

Numerical simulation of angled-injected liquid jet breakup in supersonic crossflow by a hybrid VOF-LPT method

The breakup of angled-injected liquid jets in supersonic airflow is investigated numerically by a hybrid Volume of Fluid and Lagrangian Particle Tracking (VOF-LPT) method. A Multi-criterion adaptive mesh refinement (AMR) procedure and dynamic load balancing (DLB) algorithm are applied to improve the accuracy of interface and shock wave characteristics and reduce the use of computational resources and liquid mass loss. The flow characteristics of the spray field and penetration depth of the angled-injected liquid jet from the simulations agreed well with the experimental results. Under the supersonic crossflow conditions, the jet has momentum in the counter-flow direction that improves gas-liquid interactions. The penetration depth of the liquid jet increase with the increase of the injection angle. In particular, the penetration depth of the angled-injected liquid jet is given in the: y/d=0.12·sin(2θ/3)·(esin(2θ/3))3.185·q0.389(x/d)0.309. Moreover, the liquid jet at a larger injection angle has a larger spray spread angle and wider wake region due to the larger windward area. Furthermore, the total pressure loss of airflow increases with the injection angle increasing. Considering the total pressure loss for all injection conditions is lower than 14%, the total pressure loss caused by the injection angle increase can be negligible.

Research on the Transport of Typical Pollutants in the Yellow Sea with Flow and Wind Fields

In this study, we developed a transport model for typical pollutants in the Yellow Sea using the Lagrangian particle tracking method to analyze the trajectories of fish feed, a common pollutant in the Yellow Sea. The model incorporates the influence of ocean currents and surface winds on pollutant transport and utilizes a series of numerical experiments to simulate pollutant transport. Through statistical analysis of the numerical experiment results, we identified characteristic circles that represent the pollutant distribution patterns. Furthermore, based on the current and wind information within these characteristic circles, we derived an empirical formula to describe pollutant distribution. This formula enables us to predict the spatial distribution of pollutants using available current and wind data. Using this empirical formula, we designed an effective path to avoid pollutant contamination. This approach not only optimizes the utilization of computational resources within the study area but also contributes to the rational planning of navigation routes for aquaculture vessels. Overall, our study provides valuable insights into the transport behavior of fish feed pollutants in the Yellow Sea. The establishment of the empirical formula and the design of effective routes to avoid pollution contribute to the efficient management of pollution and facilitate the planning of marine activities in the region.

Performance Improvement of Kerosene Fuelled Scramjet Combustor Through Modified Fuel Injection - A Cfd Study

Full scale kerosene fuelled scramjet combustor of a hypersonic air-breathing vehicle is numerically explored for two different fuel injection systems. A commercial software CFXTASCflow has been used for the reacting flow computation within the combustor. Three dimensional Navier-Stokes equations are solved along with k-ε turbulence model to analyse the flow field. Eddy Dissipation Model (EDM) with fast rate chemical kinetics is used for combustion modeling. Lagrangian Particle Tracking Method (LPTM) has been used to simulate the trajectory of the kerosene droplets. Kerosene is injected from the struts. Reacting flow simulations have been carried out for the fuel equivalence ratio of 1.0. The overall flow characteristics in the combustor are presented through the distribution of various thermochemical parameters at different cross sections. Kerosene which is injected in liquid phase completely vaporizes within the combustor. Considerable improvement in the performance in terms of thrust and combustion efficiency is observed with the modified fuel injection system.

LES of a turbulent lifted methanol spray flame using a novel spray flamelet/progress variable model

Turbulent spray flames are complex combustion configurations and are difficult to be accurately simulated. In this paper, we focus on further development and validation of the two-phase spray flamelet/progress variable (TSFPV) model, which is first proposed in our previous work and shows sound performance because it is able to consider the effect of droplet evaporation on the flamelet structure. A spray evaporation source term (SEST) model is improved in the present work to model the evaporation sources and is applied to the calculation of one-dimensional laminar counterflow flames to generate the spray flamelet library. The SEST model is validated on the configuration of two-dimensional counterflow spray flames, and the a priori and a posteriori results show good agreement with the solutions using the Lagrangian particle tracking (LPT) method. The effect of pre-vaporized fuel vapor is further considered in the spray flamelet library, in which both the spray and gaseous flame regimes are covered. The TSFPV model is well validated on the configuration of the laminar mixing layer by comparing the a priori and a posteriori results with detailed chemistry (DC) solutions. Large Eddy Simulation (LES) of the Sydney turbulent lifted methanol spray flame Mt2A is conducted using the TSFPV model. The flame lift-off is correctly captured and the final predicted lift-off height is very close to the experimental value. The predicted mean droplet velocities show good agreement with experimental measurements, and the rms velocities agree well with the experimental data at downstream locations with a late jet breakup. The droplet size increases along the downstream direction and this trend is well reproduced in the current simulation, though the local peak value of droplet size near the upstream shear layer is not well captured. The central jet temperature at upstream locations is also well predicted by the TSFPV model. Overall, the results show good agreement with the experimental measurements, which illustrates the potential of the TSFPV model for spray combustion modeling.

Numerical simulation research of the transportation and distribution characteristics on sea surface of the microplastic released continuously for 12 years from China's coastal cities

Based on the Lagrangian random walk particle tracking method and the global ocean reanalysis data, this study simulated the drift-diffusion process in ocean of microplastic particles (density less than seawater) discharged by coastal cities in China for 12 consecutive years. The results reveal that most of the microplastics (80.33%) essentially end up ashore or in the marginal seas around China, a small portion of microplastics (18.22%) enter the Sea of Japan and the Northwest Pacific Ocean via the Tsushima Strait and the Osumi-Kaikyo with the Kuroshio Tide, a very small portion of microplastics (1.45%) enter into the waters of Southeast Asian countries along with the west boundary current of South China Sea. The concentration distribution characteristics have obvious seasonal variation in the high concentration areas (the marginal seas around China and Sea of Japan). The mainly destination area of microplastics released in different cities is different.

Numerical investigation on dynamic characteristics of flow field in cyclone separators with different dust hopper structures

The dynamic characteristics of flow field in cyclone separators with different dust hopper structures were studied by coupling Reynolds Stress Model (RSM) and Lagrangian Particle Tracking (LPT) methods. The characteristic frequencies of cylinder section, cone section and dust hopper were calculated as f1 = 53 Hz, f2 = 65 Hz, and f3 = 8 Hz by using Fast Fourier Transform (FFT) method, respectively. Based on the effects of f3 on the motion of vortex, the separated space was divided into none affected region, weakly affected region, and strongly affected region. The characteristic frequency of dust hopper increased with the decrease of dust hopper diameter, while it was independent of the height. The dust hopper with d = 1.5D (model D3) and h = 1.5D (model H3) can significantly decrease the effect of back-mixing on the motion of inner vortex, which is beneficial to improve the efficiency of cyclone separator.

Mass transport pattern and mechanism in the tide-dominant Bohai Sea

Based on a numerical hydrodynamic model and Lagrangian particle tracking method, the Lagrangian flow network and the Lagrangian residual velocity were derived to exhibit the mass transport pattern in the tide-dominant Bohai Sea. The characteristics of the Lagrangian flow network, represented by degree and hydrodynamic provinces, show distinct regional features in the Central Basin and the three bays. The first-order Lagrangian residual velocity (i.e., the mass transport velocity) can be well maintained over a dozen averaging tidal periods, with its magnitude slightly decreasing with the increasing number of tidal periods. The second-order Lagrangian residual velocity (i.e., the Lagrangian drift velocity) includes the dependence on the initial tidal phase, which is also weakened with the increasing number of tidal periods. The mechanism behind the above two features of the Lagrangian residual velocity is explained theoretically. In the Bohai Sea, with about 15 averaging tidal periods, the Lagrangian residual velocity is approximately independent of the initial tidal phase and close to the mass transport velocity. The streamlines of the Lagrangian residual velocity averaged over 15 tidal periods are parallel to the province boundaries in the Lagrangian flow network, which means that the Lagrangian flow network is determined by the Lagrangian residual current. This may lay the foundation for using Lagrangian flow network to analyze and quantify flow and transport pathways in shallow, tide-dominated coastal regions.

О влиянии диффузии на точность измерения расхода жидкости методом лагранжевых меток

By solving a one-dimensional scalar transport equation with diffusion, it is shown that the diffusion effect can lead to an overestimation of the velocity determined by the Lagrangian particle tracking method, which consists in measuring the time of passage of a flow tracer between two sensors located in the channel. To obtain model signals, the transport equation was solved numerically for different initial scalar distributions, after which the scalar values at two spatial points were recorded. It is shown that in liquid metals characterized by high electrical and thermal conductivity, the effect can be no-ticeable. The limiting Peclet number, starting from which diffusion effects do not introduce error into measurements, was determined. It is shown that for high-frequency signals the diffusion effect will not manifest itself due to the rapid attenuation of perturbations. The paper provides estimates of Peclet numbers with turbulent transfer coefficients taken into account. It is shown that in developed turbulent flows the diffusion effect can appear due to a significant contribution of small-scale turbulence.

Automatic selection of release plane for Lagrangian-based wind-driven rain studies

Wind-driven rain (WDR) modelling based on Lagrangian particle tracking (LPT) involves the trajectory simulation of raindrops released from a horizontal plane in the computational domain. Usually, the release location is determined in a tedious trial-and-error manner, which impairs the adoption of LPT method for WDR studies in terms of user’s handiness and computational efficiency. In this study, the analytical solution for raindrop trajectories in an unobstructed domain are derived and presented. Based on the analytical solution, the location and sizes of the release plane can be easily determined a priori. A constant scaling factor can be further introduced to address possible obstruction effects by buildings. Unnecessary and expensive repetition of simulations to search for a proper release plane can be avoided, especially for scenario studies involving multiple raindrop sizes. In this paper, the accuracy, efficiency and effectiveness of the proposed automatic selection of release plane based on the analytical solutions are demonstrated based on selected case studies. It is deemed that the proposed innovative procedure for the determination of an effective and appropriate release plane can promote the widespread adoption of LPT approach for WDR studies.

Application of deep learning neural networks for the analysis of fluid-particle dynamics in fibrous filters

A novel hybrid data-driven framework was introduced in this study for the prediction of fluid-particle dynamics of submicron particles under hydrodynamic and Brownian forces in fibrous filters. The distribution of flow parameters was predicted by a high-resolution flow surrogate model based on a deep convolutional neural network (CNN) coupled with a Lagrangian particle tracking method based on the discrete phase model (DPM). The CNN-DPM model was applied to a group of several nonuniformly distributed fibers to calculate filtration efficiency. For CNN training, ground-truth data were obtained using a two-dimensional computational fluid dynamics (CFD) model for laminar incompressible flow. A simulation speedup of three orders of magnitude was obtained by CNN for predicting the velocity components and static pressure distribution within an error range of ±10%. The generalizability of CNN model was also confirmed for overlapped irregular fiber shapes and porosities out of the range of the training dataset with deviations in a range of ±20% in comparison with CFD results. The collection efficiency by CNN-DPM for small particle diameters with dp≤0.3μm was overestimated by approximately 3 % while agreeing well with CFD-DPM for larger particles. The errors of flow velocity predictions by CNN near the fibers added more randomness to the particle motion which was combined with the random Brownian motion of particles, consequently increasing the probability of the small particle hit number and filtration efficiency. The overall acceptable accuracy of the CNN-DPM was confirmed, which is suitable for fibrous filter design and optimization purposes that require thousands of simulations.