Lagrangian Particle Tracking Method Research Articles

Development of a hybrid multi-scale simulation approach for spray processes

This paper presents a multi-scale approach coupling a Eulerian interface-tracking method and a Lagrangian particle-tracking method to simulate liquid atomisation processes. This method aims to represent the complete spray atomisation process including the primary break-up process and the secondary break-up process, paving the way for high-fidelity simulations of spray atomisation in the dense spray zone and spray combustion in the dilute spray zone. The Eulerian method is based on the coupled level-set and volume-of-fluid method for interface tracking, which can accurately simulate the primary break-up process. For the coupling approach, the Eulerian method describes only large droplet and ligament structures, while small-scale droplet structures are removed from the resolved Eulerian description and transformed into Lagrangian point-source spherical droplets. The Lagrangian method is thus used to track smaller droplets. In this study, two-dimensional simulations of liquid jet atomisation are performed. We analysed Lagrangian droplet formation and motion using the multi-scale approach. The results indicate that the coupling method successfully achieves multi-scale simulations and accurately models droplet motion after the Eulerian–Lagrangian transition. Finally, the reverse Lagrangian–Eulerian transition is also considered to cope with interactions between Eulerian droplets and Lagrangian droplets.

Numerical Investigation of Inclusion Behaviour in a Multi-Strand Tundish During Strand Blockages

Inclusion removal in the continuous casting tundish is an essential technology for production of high-grade steels. In the present study, a three dimensional numerical investigation has been carried out on six strand delta shape tundish. The aim of the work is to investigate the inclusion entrapment and removal phenomenon in a tundish. A parametric study has been carried out to study the behavior of the inclusions in a steelmaking tundish and the results have been compared on the basis of densities and diameters of inclusions. Bare tundish as well as a tundish occupied with Advance Pouring Box (APB) have been studied to predict the transport behavior of inclusion particles. Further, effect of strand blockages has been considered. The turbulent Navier–Stokes equations have been solved to predict the flow velocity distributions and inclusion trajectories were calculated using a Lagrangian particle tracking method. The numerical results were validated using available experimental results and found to be in good agreement. The results indicate that the use of APB has changed the fluid flow pattern and consequently the inclusion particles movement. The density of inclusion particles plays an important role. It has been seen that low dense particles have higher chances to get trapped or removed from tundish. It was also found that larger diameter of inclusion particles have more chances of floatation.

Computational Fluid Dynamics Simulation of Tip-to-Tail for Hypersonic Test Vehicle

Computational fluid dynamics simulations are carried out for a complete hypersonic vehicle integrating both external (nonreacting) and internal (reacting) flow together to calculate the scramjet combustor performance and vehicle net thrust minus drag. Simulations are carried out for a flight Mach number of about six. Three-dimensional Navier–Stokes equations are solved along with the shear stress transport turbulence model and single-step chemical reaction based on fast chemistry. The Lagrangian particle tracking method for droplets is used for combustion of kerosene fuel. Flow is largely nonuniform at the inlet of the combustor. Mass flow of ingested air increases with increase in angle of attack. Because of more combustion of fuel, wall surface pressure is higher for compared with . Combustion efficiency and thrust achieved are found to increase with the increase in angle of attack. Considerable amount of thrust is obtained from a single expansion ram nozzle and achievement of positive thrust–drag for the whole vehicle is demonstrated. The computational analysis of the whole vehicle provides net forces and moments of the whole vehicle, which is very useful for the mission analysis of the vehicle.

Interregional differences in mortality of aquacultured yellowtail Seriola quinqueradiata in relation to a Chattonella bloom in the Yatsushiro Sea, Japan, in 2010

Mass mortality of Seriola quinqueradiata was caused by a Chattonella bloom in summer 2010 in the southern area of the Yatsushiro Sea. We analyzed the diurnal records of the mortality occurrence and cell density of C. marina to examine the short-term mortality dynamics. In addition, a hydrodynamic model and Lagrangian particle tracking method were used to examine interregional differences in the mortalities. Mortalities were concentrated along the southern coast of Shishi Island and western coast of Nagashima Island in early July. In late July, mortalities occurred along the southern coast of Shishi Island and eastern coast of Nagashima Island. Severe mortalities occurred where the bloom (>100 cells ml−1 of Chattonella marina) appeared in both early and late July. Model results show that interregional difference of the bloom was controlled by the advection system in the Yatsushiro Sea. The consistent spatio-temporal pattern between fish mortalities and bloom dynamics indicates the potential benefits of real-time monitoring of harmful algae and assessing factors controlling hydrographic conditions to mitigate mortalities.

Towards High-fidelity Multi-scale Simulation of Spray Atomization

Abstract Liquid jet atomization is an important process in internal combustion engine. This paper presents a multi-scale approach coupling a Eulerian interface-tracking method and a Lagrangian particle tracking method to simulate liquid atomization processes. This method aims to capture the complete spray atomization process, particularly primary and second breakup, paving the way for high-fidelity simulation of spray atomization in the dense spray zone and spray combustion in the dilute spray zone. The Eulerian method is based on the Coupled Level-Set and Volume-of-Fluid (CLSVOF) for interface tracking, which can accurately simulate the primary breakup process. For the coupling approach, the Eulerian method only describes large droplet and ligament structures, while small-scale droplet structures are removed from the resolved Eulerian description and transformed into Lagrangian point-source droplets. The Lagrangian method is thus used to track small droplets and their further secondary breakup and collision. In this study, two-dimensional simulation of liquid jet atomization is performed. We will analyse Lagrangian-droplet formation and motion due to the coupling and the atomization characteristics using the multi-scale approach.

The Effects of Patient Movement on Particles Dispersed by Coughing in an Indoor Environment

This study investigates the influence of a moving patient on the transport characteristics of coughing particles by dy­ namic meshing and the Lagrangian particle tracking method. Through simulation, particle movement during the initial coughing, patient movement, and stationary flow phases was examined. Two different particle sizes (5 µm and 10 µm) were used and yielded small differences in the initial airflow after coughing. During the patient-moving phase, the temporal parti­ cle distribution in the upper, breathing, lower, and near-floor zones were simulated. The amplified air-velocity field induced by the moving patient enhanced the particle entrainment, thus increasing the risk of contamination (defined as particle sys­ tem entropy) in the whole room. Both temporal and final parti­ cle distribution during the stationary flow phase were studied. Walking speed affected the particle distribution in the traveling direction, but not in the vertical or lateral directions at the end of the simulation. Turbulence dispersion played a critical role in the spread of the particles through the coughing and patient- moving phases.

Computational fluid dynamics simulation and parametric study of an open channel ultra-violet wastewater disinfection reactor

The disinfection characteristics of an open channel ultra-violet (UV) disinfection reactor is investigated numerically. The computational fluid dynamics (CFD) model used in this study is based on the volume of fluid (VOF) method to capture the water–air interface. The Lagrangian particle tracking method is used to calculate the microbial particle trajectory and the discrete ordinate (DO) model is used to calculate the UV intensity field inside the reactor. A commercial CFD software package ANSYS FLUENT is used to solve the governing equations. Custom user defined functions (UDFs) are developed to calculate the UV doses. A post-processor is developed in MATLAB to implement the inactivation kinetics of the microbes. The post-processor provides the probabilistic dose distribution and reduction equivalent dose (RED) values achievable in the reactor. The numerical predictions are compared with available experimental data to validate the CFD model. A parametric study is performed to understand the effects of different parameters on disinfection performance of the reactor. The low/high dosed particle trajectories, which can provide an insight for hydraulic and optical characteristics of the reactor for possible design improvements, are identified.

Research on heavy-duty gas turbine vane high efficiency cooling performance considering coolant phase transfer

Conjugate simulation for heavy-duty gas turbine vane of mist/air phase transfer cooling is carried out to evaluate the cooling enhancement. The Eulerian–Lagrangian particle tracking method is adopted to investigate the two-phase cooling for a gas turbine vane. The accuracy of numerical simulation program for conjugate heat transfer methodology is verified with the C3X gas turbine vane cooled with leading film holes. The effect of various parameters including mist concentration and mist diameter on the cooling performance improvement is investigated in this paper. Results show that the average blade surface temperature reduction about 90 K, 119 K and 94 K are achieved at hub section, midspan section and tip section with 8% mist injection. This translates into a significant blade surface cooling effectiveness enhancement of 11%, 15% and 11%, respectively. The disparate trends are shown for the influence of mist diameter on the blade cooling performance at different spanwise and chordwise location, the results indicate that the degree and the location of cooling performance can be controlled by manipulating different sizes of injected water mist.

Seasonal migration of the Yellow Sea Bottom Cold Water

AbstractThe three‐dimensional motion of the Yellow Sea Bottom Cold Water (YSBCW) and the relevant dynamical factors are studied using a regional circulation model and the two‐way Lagrangian particle tracking method (PTM). The simulated results are in good agreement with hydrographic observations. The trajectories of the modeled particles show that the subsurface cold heavy water mass from the northern part of the Yellow Sea gradually sinks into deeper layers along the western slope of the Yellow Sea trough with a southward movement from spring to summer. The cold water mass gradually gathers speed from early March to July or August, and eventually reaches its southernmost location in late September or early October. Furthermore, sensitivity experiments demonstrate that tide‐induced residual currents under baroclinic conditions are the dominant factor driving deep circulation during summertime in the Yellow Sea. The summer southerly wind and strong surface solar radiation are the secondary factors influencing the southward migration. This study also proposes an improved delimitation for the YSBCW based on temperature statistics in the central basin (deeper than 40 m) between 35°N and 39°N in March with an increase in rate of approximately 0.7°C/month, which is more appropriate than the constants of the 8°C or 10°C isotherms frequently used.

Simulating blade-strike on fish passing through marine hydrokinetic turbines

The occurrence, frequency, and intensity of blade-strike of fish on an axial-flow marine hydrokinetic turbine was simulated using two modeling approaches: a novel scheme combining computational fluid dynamics (CFD) with Lagrangian particle tracking, and a conventional kinematic model. The kinematic model included simplifying assumptions of fish trajectories such as distribution and velocity. The proposed CFD and Lagrangian particle tracking methods provided a more realistic representation of blade-strike mechanisms by integrating the following components: (i) advanced unsteady turbulence simulation using detached eddy simulation (DES), (ii) generation of inflow turbulence based on field data, (iii) moving turbine blades in highly transient flows, and (iv) Lagrangian particles to mimic the potential fish pathways. The test conditions to evaluate the blade-strike probability and fish survival rate were: (i) the turbulence environment, (ii) the fish size, and (iii) the approaching flow velocity. The proposed Lagrangian method simulates potential fish trajectories and their interaction with the rotating turbine with the limitation that it does not include any volitional fish avoidance behavior. Depending upon the scenario, the percentage of particles that registered a collision event ranged from 6% to 19% of the released sample size. Next, by using a set of experimental correlations of the exposure-response for live fish colliding with moving blades, the simulated collision data were used as input variables to estimate the survival rate of fish passing through the operating turbine. The resulting survival rates were greater than 96% in all scenarios, which is comparable to or better than known survival rates for conventional hydropower turbines. The kinematic model predicted higher blade-strike probabilities and mortality rates than the Lagrangian particle-based method did. The Lagrangian method also offers the advantage of expanding the evaluation framework to include additional mechanisms of stress and injury on fish, or other aquatic biota, caused by hydrokinetic turbines and related devices.

Numerical validation of a near-field fugitive dust model for vehicles moving on unpaved surfaces

This paper presents a numerical model for evaluating fugitive dust emissions and transport in a near field induced by a moving vehicle. The dust emission model describes the quantity and location of emitted dust. The transport of the dust is recorded by the Lagrangian particle-tracking method, and the turbulence dispersion of particles is modeled stochastically. The presented model is validated numerically for the prediction of dust concentration in a region near the vehicles through a careful comparison with the available experimental data. The simulation results compare reasonably well with the experimental data. This model provides, for the first time, a validated dust emission and transport model suitable for the near field of moving vehicles.

Numerical study on tidal currents and seawater exchange in the Benoa Bay, Bali, Indonesia

A three-dimensional (3-D) finite volume coastal ocean model (FVCOM) was used for the study of water circulation and seawater exchange in the Benoa Bay, Bali Island. The M2 tidal component was forced in open boundary and discharge from six rivers was included in the numerical calculation. The M2 tidal elevation produced by the FVCOM has a good agreement with the observation data. The M2 tidal current is also successfully calculated under the ebb tide and flood tide conditions. The non-linear M2 tidal residual current was produced by the coastline geometry, especially surrounding the narrow strait between the Serangan Island and the Benoa Peninsula. The tidal residual current also generated two small eddies within the bay and one small eddy in the bay mouth. The salinity distribution influenced by river discharge could be successfully calculated, where the numerical calculation and the observation results have a good correlation (r 2) of 0.75. Finally in order to examine the seawater exchange in the Benoa Bay, the Lagrangian particle tracking method and calculation of residence time are applied. The mechanism of particle transport to the flushing of seawater is depicted clearly by both methods.

Computational investigation of the mechanisms of the “breakaway” effect in a dense medium cyclone

The motion of coal particles and the “breakaway” effect in an industrial dense medium cyclone of body diameter 1000mm are studied by a computational fluid dynamics model. In the model, mixture multiphase model is employed to describe the flow of the dense medium (comprising finely ground magnetite contaminated with non-magnetic material in water) and the air core, where the turbulence is described by the well-established Reynolds Stress Model. The stochastic Lagrangian Particle Tracking method is used to simulate the flow of coal particles. It is shown that for coarse coal particles with size larger than 1mm, the separation is mainly determined by the difference between the inward pressure gradient force and the outward centrifugal force, and the effect of drag force can be ignored. For finer particles with size less than 1mm, however, the effect of stochastic drag force becomes significant. As a result, fine particles have an apparent fluctuating velocity and a relatively uniform distribution in the cyclone; and the drag force is so dominant that particles flow with fluid closely and the pressure gradient force is relatively so small to be able to effectively separate particles by density in the radial direction. This results in a significantly deteriorated separation efficiency of fine particles and the “breakaway” effect.

Optimization of SO2 Scrubber Using CFD Modeling

The reduction of environmental contaminants that contribute to smog and soot is a worldwide goal that has seen an increased focus in recent years. In the United States, for example, it is estimated that by 2014 new rules will lead to a 71% reduction of sulfur dioxide emissions and 52% of nitrogen oxide emissions as compared to 2005 level. Thus, medium-sized plants (100-500MW) that currently do not have flue gas desulfurization (FGD) units or selective catalytic reduction systems (SCRs) will be required to adapt. Similar emission reduction efforts are expected to be adopted globally, albeit at different levels. Wet-scrubber FGD is characterized as one of the most effective SO2 removal techniques with low operating costs. However capital cost for implementation is considered high. Hence an effective optimization procedure is required to reduce these capital costs of conversion.Power plants commonly use a lime slurry spray reaction to reduce SO2 emissions. Control of the droplets throughout the tower geometry is essential to ensuring maximum reduction while minimizing scale. The liquid slurry is known to have density, surface tension and viscosity values that deviate from standard water spray characteristics, which complicates process optimization. In order to improve the scrubber, nozzle characteristics and placement must be optimized to reduce the cost of the system implementation and mitigate risks of inadequate pollution reduction. A series of large flow rate, hydraulic, hollow cone sprays were investigated for this study.A Computational Fluid Dynamics (CFD) model was used to examine potential scrubber designs for optimization of the system. Nozzle parameters were modeled to allow particle tracking through the system. An ANSYS Fluent Lagrangian particle tracking method was used with heat and mass transfer. The alkaline sorbent material and SO2 reaction is modeled to determine uniformity and efficacy of the system. Volumetric chemistry mechanisms were used to simulate the reaction. These results demonstrate the expected liquid-gas interaction relative to the system efficiency. Drop size, liquid rheology, and spray array layout were examined to achieve SO2 removal above 90%. Wall impingement and flow pattern results were evaluated due to their impact in minimizing equipment plugging and corrosion required as for long-term scrubber utilization.

Large eddy simulation of particulate flow inside a differentially heated cavity

In nuclear safety, some severe accident scenarios lead to the presence of fission products in aerosol form in the closed containment atmosphere. It is important to understand the particle depletion process to estimate the risk of a release of radioactivity to the environment should a containment break occur. As a model for the containment, we use the three-dimensional differentially heated cavity problem. The differentially heated cavity is a cubical box with a hot wall and a cold wall on vertical opposite sides. On the other walls of the cube we have adiabatic boundary conditions. For the velocity field the no-slip boundary condition is applied. The flow of the air in the cavity is described by the Boussinesq equations. The method used to simulate the turbulent flow is the large eddy simulation (LES) where the dynamics of the large eddies is resolved by the computational grid and the small eddies are modelled by the introduction of subgrid scale quantities using a filter function. Particle trajectories are computed using the Lagrangian particle tracking method, including the relevant forces (drag, gravity, thermophoresis). Four different sets with each set containing one million particles and diameters of 10μm, 15μm, 25μm and 35μm are simulated. Simulation results for the flow field and particle sizes from 15μm to 35μm are compared to previous results from direct numerical simulation (DNS). The integration time of the LES is three times longer and the smallest particles have been simulated only in the LES. Particle statistics in the LES and the DNS were similar and the settling rates were practically identical. It was found that for this type of flow no model was necessary for the influence of the unresolved flow scales on the particle motions. This can be explained by the dominant nature of gravity settling compared to turbophoresis which is negligible for the particle sizes of the present study.

Potential impact of heterogeneity on groundwater age

Groundwater age is an important water property used as an indicator of groundwater quality. There have been no sufficient data and measurements underground, and that problem has been mitigated by using direct simulation of groundwater age. This paper has been motivated by the work of Daniel J. Goode, defining a rather different approach. A numerical model has been developed, using the Lagrangian approach and random walk particle tracking method, where groundwater age is calculated as a summed-up travelling time of certain particles. Basic input of this method is flow calculation; hence, in order to get the groundwater age simulation, an upgrade has been done to the existing software. Synthetic examples have been simulated for homogeneous, layered, as well as for low and medium heterogeneous aquifer systems. A stochastic analysis of heterogeneous aquifers has been done using a Monte Carlo simulation method. The results are given as groundwater age fields. Application of such an approach lays in possible estimation of the expected groundwater age at a certain location of water intake. Therefore, the calculated probability assumptions may be used as a decision support tool in cases of groundwater pollution, estimation of the level of aquifer's auto-purification, or in events where applying certain level of water treatment prior to usage is needed.

An Analysis of Loop Current Frontal Eddies in a ⅙° Atlantic Ocean Model Simulation

Abstract The Loop Current frontal eddies (LCFEs) refer to cyclonic cold eddies moving downstream along the outside edge of the Loop Current in the eastern Gulf of Mexico. They have been observed by in situ measurements and satellite imagery, mostly downstream of the Campeche Bank continental shelf. Their evolution, simulated by a primitive equation ⅙° and 37-level Atlantic Ocean general circulation numerical model, is described in detail in this study. Some of the simulated LCFEs arise, with the passage through the Yucatan Channel of a Caribbean anticyclonic eddy, as weak cyclones with diameters less than 100 km near the Yucatan Channel. They then grow to fully developed eddies with diameters on the order of 150–200 km while moving along the Loop Current edge. Modeled LCFEs have a very coherent vertical structure with isotherm doming seen from 50- to ~1000-m depth. The Caribbean anticyclone and LCFE are two predominant features in this numerical model simulation, which account for 22% and 10%, respectively, of the short-term (period less than 100 days) temperature variance at 104.5 m in the complex empirical orthogonal function (CEOF) analysis. The source water inside the LCFEs that are generated by Caribbean anticyclonic eddy impingement can be traced back, using a backward-in-time Lagrangian particle-tracking method, to the western edge of the Caribbean Current in the northwest Caribbean Sea and to coastal waters near the northern Yucatan Peninsula. The model results indicating a pairing of anticyclonic and cyclonic eddies within and north of the Yucatan Channel are supported by satellite altimetry measurements during February 2002 when several altimeters were operational.

An efficient lattice Boltzmann model for indoor airflow and particle transport

The three-dimensional multiple-relaxation-time LB (MRT-LB) and Lagrangian particle tracking methods were applied to simulate turbulent airflow and particle dispersion in a ventilated room with a partition. The turbulent airflow was simulated by large eddy simulation (LES) using the MRT-LB method with the Smagorinsky model. This method was verified by comparing it with experimental and other numerical results. Good agreement was observed between airflow simulation and experimental data. It is also demonstrated that the LES carried out by the MRT-LB method can produce airflow results very similar to the RNG LES and provide better prediction than the standard and RNG k–ε models. In order to further improve the efficiency of the MRT-LB method, the multi-block grid refinement (MBGR) technique was used. The accuracy and efficiency of the MBGR and the consistency of physical quantities across the interface were investigated. In simulation of particle dispersion in the model room, particles with diameters of 1 and 10 µm were considered. It is shown that this model can successfully capture dispersion characteristics of particles.

A222 高圧条件下における予混合気自着火及び火炎伝播の直接数値計算(OS-1:火災安全・燃焼(5))

Direct numerical simulations of autoignition have been conducted to clarify effects of length scale in flow and temperature field and initial temperature fluctuations on turbulent combustion mechanisms in homogeneous charge compression ignition engines. Methane-air mixtures at high pressure with spatial inhomogeneity of temperature are investigated by considering a detailed kinetic mechanism. For the case with lower temperature fluctuations, local autoignition starts later at smaller length scale due to larger effects of turbulent and molecular diffusion before the autoignition, while effects of length scale is relatively weak for high temperature fluctuations. Lagrangian fluid particle tracking method is conducted to identify combustion regimes under the different length-scale conditions.

CFD simulation and validation of wind-driven rain on a building facade with an Eulerian multiphase model

Wind-driven rain (WDR) is one of the most important moisture sources with potential negative effects on hygrothermal performance and durability of buildings. The impact of WDR on building facades can be understood in a better way by predicting the surface wetting distribution accurately. Computational Fluid Dynamics (CFD) simulation with the Lagrangian particle tracking (LPT) method has been widely used and validated by several researchers for different isolated building configurations. In this paper, Eulerian Multiphase modeling (EM) for WDR assessment is applied and validated for a monumental tower building (St. Hubertus building in The Netherlands). The LPT and EM models show comparable results and EM is validated by comparison of the calculated catch ratio values with available experimental data on windward facade. The deviations between the experimental and the model results at low rain intensity and wind speed are attributed to the absence of turbulent dispersion in both LPT and EM models. EM has the advantages, first, of less computational complexity and faster pre-processing and post-processing in terms of raindrop trajectories and WDR catch ratios, and second, of allowing the calculation of catch ratios on all surfaces of a complex geometry over the domain at once. The user time spent for the simulation decreases by at least a factor of 10 using EM instead of LPT for a single building. Additionally, the EM is expected to provide a sound basis for future WDR studies incorporating more accurate calculation of the wind flow field, e.g. by LES and the inclusion of turbulent dispersion.