Time-Dependent Simulation of a Swirling Two Phase Flow Using an Anisotropic Turbulent Dispersion Model

2005 ◽  
Author(s):  
Justus Lipowsky ◽  
Martin Sommerfeld
Keyword(s):  
Disperse Phase ◽  
Dispersion Model ◽  
Continuous Phase ◽  
Swirl Flow ◽  
Particle Dispersion ◽  
Turbulent Dispersion ◽  
Time Dependent ◽  
Particle Collision ◽  
Time Step ◽  
Lagrange Approach

Time-dependent simulations of a particle-laden swirl flow in a pipe expansion based on the Euler-Lagrange approach are presented. Two equation and Reynolds Stress Models were used in the calculation of turbulent quantities in the continuous phase. Additional attention was payed to the influence of particle dispersion. The instantaneous fluid velocities seen by the particles was reconstructed by different dispersion models. To come to a time dependant solution for the Euler-Lagrange approach, a quasi-unsteady approach is taken. This results in a calculational scheme where one Eulerian time-step is divided in a number of Lagrangian steps. Particle source term are sampled which represent the influence of the disperse phase on the flow field. which call for additional coupling within one Eulerian time step. The effect of inter-particle collisions on the movement of the disperse phase is accounted for using a stochastic inter-particle collision model. Special interest of this study was the formation of dust ropes which are observed in such flows.

Development of a Hybrid Turbulent Particle Dispersion Model and Implementation in the Gasflow Code

2008 ◽  
Author(s):  
Zhanjie Xu ◽  
John R. Travis ◽  
Wolfgang Breitung
Keyword(s):  
Dispersion Model ◽  
Separated Flow ◽  
Particle Dispersion ◽  
Turbulent Dispersion ◽  
Vacuum Vessel ◽  
Dispersion Models ◽  
Proposed Model ◽  
Dust Mobilization ◽  
Decaying Turbulence ◽  
Turbulent Particle Dispersion

Dust mobilization in a vacuum vessel is one of the key issues endangering the security of the International Thermonuclear Experimental Reactor (ITER), in case of Loss of Vacuum Accidents (LOVA). The turbulent behavior of particles in turbulent flows has to be modeled for successful numerical simulations about particle mobilization. In this study a Lagrangian approach is adopted to formulate the particle transport especially for dust-dilute flows mostly encountered in the vacuum vessel of ITER. Based on the logic frame of the approach and the used Computational Fluid Dynamic (CFD) computer code in the study, a hybrid turbulent particle dispersion model is proposed. The hybrid model features both a deterministic separated flow (DSF) model and a stochastic separated flow (SSF) model, which are two popular turbulent dispersion models applied in particle simulations, and takes the advantages of the both models. The proposed model is implemented into the particle model of the CFD code successfully and the simulation results are verified against experimental data. The verifications manifest the validities of the proposed model. In this paper general information about the work of dust mobilization is introduced and the particle turbulent dispersion models are reviewed briefly at first. The hybrid model is then proposed based on the SSF model. An experiment about particle dispersions in an advective wind channel flow with decaying turbulence in the streamwise direction is reviewed in the third section. In the following section about model verification, the decaying turbulence parameters in the channel flow are verified against experimental data as the first step, the parameters about the particle dispersions in the verified flow field are then verified against the data. The work is concluded finally.

Development of a Hybrid Turbulent Particle Dispersion Model and Implementation in the Gasflow Code

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Zhanjie Xu ◽  
John R. Travis ◽  
Wolfgang Breitung
Keyword(s):  
Dispersion Model ◽  
Separated Flow ◽  
Particle Dispersion ◽  
Turbulent Dispersion ◽  
Vacuum Vessel ◽  
Dispersion Models ◽  
Proposed Model ◽  
Dust Mobilization ◽  
Decaying Turbulence ◽  
Turbulent Particle Dispersion

Dust mobilization in a vacuum vessel is one of the key issues endangering the security of the International Thermonuclear Experimental Reactor (ITER) in case of loss of vacuum accidents. The turbulent behavior of particles in turbulent flows has to be modeled for successful numerical simulations about particle mobilization. In this study a Lagrangian approach is adopted to formulate the particle transport especially for dust-dilute flows mostly encountered in the vacuum vessel of ITER. Based on the logic frame of the approach and the used computational fluid dynamics (CFD) computer code in the study, a hybrid turbulent particle dispersion model is proposed. The hybrid model features both a deterministic separated flow model and a stochastic separated flow (SSF) model, which are two popular turbulent dispersion models applied in particle simulations, and takes the advantages of the both models. The proposed model is implemented into the particle model of the CFD code successfully and the simulation results are verified against the experimental data. The verifications manifest the validities of the proposed model. In this paper general information about the work of dust mobilization is introduced and the particle turbulent dispersion models are reviewed briefly at first. The hybrid model is then proposed based on the SSF model. An experiment about particle dispersions in an advective wind channel flow with decaying turbulence in the streamwise direction is reviewed in the third section. In the following section about model verification, the decaying turbulence parameters in the channel flow are verified against the experimental data as the first step, and the parameters about the particle dispersions in the verified flow field are then verified against the data. The work is concluded finally.

scholarly journals Development of turbulent scheme in the FLEXPART-AROME v1.2.1 Lagrangian particle dispersion model

2019 ◽  
Author(s):  
Bert Verreyken ◽  
Jérome Brioude ◽  
Stéphanie Evan
Keyword(s):  
Dispersion Model ◽  
Particle Dispersion ◽  
Scale Model ◽  
Limited Area ◽  
Lagrangian Particle ◽  
Time Step ◽  
Limited Area Model ◽  
Area Model ◽  
South West Indian Ocean ◽  
Meso Scale

Abstract. The FLEXible PARTicle dispersion model FLEXPART, first released in 1998, is a Lagrangian particle dispersion model developed to simulate atmospheric transport over large and meso-scale distances. Due to FLEXPART's success and its open source nature, different limited area model versions of FLEXPART were released making it possible to run FLEXPART simulations by ingesting WRF (Weather Research Forecasting model) or MM5 (meso-scale community model maintained by Penn State university) meteorological fields on top of the ECMWF (European Centre for Medium-Range Weather Forecasts) and GFS (Global Forecast System) meteorological fields. Here, we present a new FLEXPART limited area model that is compatible with the AROME mesoscale meteorological forecast model (the Applications of Research to Operations at Meso-scale model). FLEXPART-AROME was originally developed to study meso-scale transport around La Réunion, a small volcanic island in the South West Indian Ocean with a complex orographic structure which is not well represented in current global operational models. The AROME vertical hybrid sigma grid is projected on the Cartesian terrain following FLEXPART grid. We present new turbulent modes in FLEXPART-AROME. They differ from each other by: dimensionality, mixing length parameterisation, turbulent transport constraint interpretation and a novel time-step configuration. Performances of new turbulent modes are compared to the ones in FLEXPART-WRF by testing the conservation of well-mixedness by turbulence, the dispersion of a point release at the surface and the marine boundary layer evolution around Reunion island. An adaptive time step for the vertical turbulent motions has been implemented to improve conservation of well-mixedness in the model.

Simulation of the Turbulent Dispersion of 10 Micron Particles in a Generic Half-Cabin Model

2011 ◽  
Author(s):  
Khosrow Ebrahimi ◽  
Zhongquan C. Zheng ◽  
Mohammad H. Hosni
Keyword(s):  
Disease Transmission ◽  
Equation Of Motion ◽  
Continuous Phase ◽  
Particle Dispersion ◽  
Turbulent Dispersion ◽  
Second Phase ◽  
Experimental Measurements ◽  
Phase Equation ◽  
Hexahedral Elements ◽  
Discrete Phase

Study of particle dispersion in ventilated indoor environments is a very useful and effective way to understand the mechanism for disease transmission in an enclosed environment. In this investigation, a computational approach is adopted in order to gain more knowledge about the transport of particulate materials in a simplified half cabin model of a Boeing 767. The simulations are performed using a commercial Computational Fluid Dynamics (CFD) software and are validated through comparing the predictions with the corresponding experimental measurements. The Lagrange-Euler approach is invoked in the simulations. In this approach, while the air is considered as the continuous first phase, the particles are treated as the discrete second phase. By solving the particles equation of motion, the trajectory of particles is computed. The discrete phase equation of motion is coupled with the continuous phase governing equations through the calculation of drag and buoyancy forces acting on particles. The continuous phase flow is turbulent and Reynolds Averaged Navier Stokes (RANS) is employed in the calculation of velocity field. A complete study on grid dependence of RANS simulation is performed through a controllable local mesh refinement scheme. The grid dependence study shows that using unstructured grid with tetrahedral and hybrid elements in the refinement region are more efficient than using structured grid with hexahedral elements. The effect of turbulence on particle dispersion is taken into account by using a stochastic tracking method (random walk model). Through the comparison of computational predictions with corresponding experimental measurements the capability of Discrete Phase Model (DPM) in predicting the behavior of particles is studied.

scholarly journals Development of turbulent scheme in the FLEXPART-AROME v1.2.1 Lagrangian particle dispersion model

2019 ◽  
Vol 12 (10) ◽  
pp. 4245-4259 ◽  
Author(s):  
Bert Verreyken ◽  
Jérome Brioude ◽  
Stéphanie Evan
Keyword(s):  
Mesoscale Model ◽  
Dispersion Model ◽  
Particle Dispersion ◽  
Small Scale ◽  
Limited Area ◽  
Lagrangian Particle ◽  
Time Step ◽  
Southwest Indian Ocean ◽  
Limited Area Model ◽  
Area Model

Abstract. The FLEXible PARTicle dispersion model FLEXPART, first released in 1998, is a Lagrangian particle dispersion model developed to simulate atmospheric transport over large and mesoscale distances. Due to FLEXPART's success and its open source nature, different limited area model versions of FLEXPART were released making it possible to run FLEXPART simulations by ingesting WRF (Weather Research Forecasting model), COSMO (Consortium for Small-scale Modeling) or MM5 (mesoscale community model maintained by Penn State university) meteorological fields on top of the ECMWF (European Centre for Medium-Range Weather Forecasts) and GFS (Global Forecast System) meteorological fields. Here, we present a new FLEXPART limited area model that is compatible with the AROME mesoscale meteorological forecast model (the Applications of Research to Operations at Mesoscale model).1 FLEXPART-AROME was originally developed to study mesoscale transport around La Réunion, a small volcanic island in the southwest Indian Ocean with a complex orographic structure, which is not well represented in current global operational models. We present new turbulent modes in FLEXPART-AROME. They differ from each other by dimensionality, mixing length parameterization, turbulent transport constraint interpretation and time step configuration. A novel time step was introduced in FLEXPART-AROME. Performances of new turbulent modes are compared to the ones in FLEXPART-WRF by testing the conservation of well-mixedness by turbulence, the dispersion of a point release at the surface and the marine boundary layer evolution around Réunion. The novel time step configuration proved necessary to conserve the well-mixedness in the new turbulent modes. An adaptive vertical turbulence time step was implemented, allowing the model to adapt on a finer timescale when significant changes in the local turbulent state of the atmosphere occur.

scholarly journals Large-Scale Atmospheric Dispersal Simulations Identify Likely Airborne Incursion Routes of Wheat Stem Rust Into Ethiopia

2017 ◽  
Vol 107 (10) ◽  
pp. 1175-1186 ◽  
Author(s):  
M. Meyer ◽  
L. Burgin ◽  
M. C. Hort ◽  
D. P. Hodson ◽  
C. A. Gilligan
Keyword(s):  
Stem Rust ◽  
Large Scale ◽  
Dispersion Model ◽  
Fungal Spores ◽  
Disease Outbreaks ◽  
Particle Dispersion ◽  
East African ◽  
Wheat Stem Rust ◽  
Sub Saharan ◽  
African Rift

In recent years, severe wheat stem rust epidemics hit Ethiopia, sub-Saharan Africa’s largest wheat-producing country. These were caused by race TKTTF (Digalu race) of the pathogen Puccinia graminis f. sp. tritici, which, in Ethiopia, was first detected at the beginning of August 2012. We use the incursion of this new pathogen race as a case study to determine likely airborne origins of fungal spores on regional and continental scales by means of a Lagrangian particle dispersion model (LPDM). Two different techniques, LPDM simulations forward and backward in time, are compared. The effects of release altitudes in time-backward simulations and P. graminis f. sp. tritici urediniospore viability functions in time-forward simulations are analyzed. Results suggest Yemen as the most likely origin but, also, point to other possible sources in the Middle East and the East African Rift Valley. This is plausible in light of available field surveys and phylogenetic data on TKTTF isolates from Ethiopia and other countries. Independent of the case involving TKTTF, we assess long-term dispersal trends (>10 years) to obtain quantitative estimates of the risk of exotic P. graminis f. sp. tritici spore transport (of any race) into Ethiopia for different ‘what-if’ scenarios of disease outbreaks in potential source countries in different months of the wheat season.

Numerical Simulation of Droplet Generation in Series Co-Flow Capillaries

2009 ◽  
Author(s):  
Yanxi Song ◽  
Jinliang Xu
Keyword(s):  
Reynolds Number ◽  
Disperse Phase ◽  
Weber Number ◽  
Three Dimensional ◽  
Continuous Phase ◽  
Disperse Flow ◽  
Double Emulsions ◽  
Wide Range ◽  
In Series ◽  
Dispersed Phases

We study the production and motion of monodisperse double emulsions in microfluidics comprising series co-flow capillaries. Both two and three dimensional simulations are performed. Flow was determined by dimensionless parameters, i.e., Reynolds number and Weber number of continuous and dispersed phases. The co-flow generated droplets are sensitive to the Reynolds number and Weber number of the continuous phase, but insensitive to those of the disperse phase. Because the inner and outer drops are generate by separate co-flow processes, sizes of both inner and outer drops can be controlled by adjusting Re and We for the continuous phase. Meanwhile, the disperse phase has little effect on drop size, thus a desirable generation frequency of inner drop can be reached by merely adjusting flow rate of the inner fluid, leading to desirable number of inner drops encapsulated by the outer drop. Thus highly monodisperse double emulsions are obtained. It was found that only in dripping mode can droplet be of high mono-dispersity. Flow begins to transit from dripping regime to jetting regime when the Re number is decreased or Weber number is increased. To ensure that all the droplets are produced over a wide range of running parameters, tiny tapered tip outlet for the disperse flow should be applied. Smaller the tapered tip, wider range for Re and we can apply.

scholarly journals Atmospheric rivers moisture sources from a Lagrangian perspective

2016 ◽  
Vol 7 (2) ◽  
pp. 371-384 ◽  
Author(s):  
Alexandre M. Ramos ◽  
Raquel Nieto ◽  
Ricardo Tomé ◽  
Luis Gimeno ◽  
Ricardo M. Trigo ◽  
...  
Keyword(s):  
North Atlantic ◽  
Dispersion Model ◽  
Local Maximum ◽  
Detection Algorithm ◽  
Ocean Basin ◽  
Particle Dispersion ◽  
Western Coast ◽  
Moisture Uptake ◽  
Lagrangian Analysis ◽  
Data Set

Abstract. An automated atmospheric river (AR) detection algorithm is used for the North Atlantic Ocean basin, allowing the identification of the major ARs affecting western European coasts between 1979 and 2012 over the winter half-year (October to March). The entire western coast of Europe was divided into five domains, namely the Iberian Peninsula (9.75° W, 36–43.75° N), France (4.5° W, 43.75–50° N), UK (4.5° W, 50–59° N), southern Scandinavia and the Netherlands (5.25° E, 50–59° N), and northern Scandinavia (5.25° E, 59–70° N). Following the identification of the main ARs that made landfall in western Europe, a Lagrangian analysis was then applied in order to identify the main areas where the moisture uptake was anomalous and contributed to the ARs reaching each domain. The Lagrangian data set used was obtained from the FLEXPART (FLEXible PARTicle dispersion) model global simulation from 1979 to 2012 and was forced by ERA-Interim reanalysis on a 1° latitude–longitude grid. The results show that, in general, for all regions considered, the major climatological areas for the anomalous moisture uptake extend along the subtropical North Atlantic, from the Florida Peninsula (northward of 20° N) to each sink region, with the nearest coast to each sink region always appearing as a local maximum. In addition, during AR events the Atlantic subtropical source is reinforced and displaced, with a slight northward movement of the sources found when the sink region is positioned at higher latitudes. In conclusion, the results confirm not only the anomalous advection of moisture linked to ARs from subtropical ocean areas but also the existence of a tropical source, together with midlatitude anomaly sources at some locations closer to AR landfalls.

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