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A CFD–DEM approach coupled with heat transfer for the melting process of a packed of particles Baniasadi, Mehdi ; Baniasadi, Maryam ; Peters, Bernhard Scientific Conference (2017, September 28) Detailed reference viewed: 128 (9 UL)Multiscale model of sintering: diffusion and plastic flow Kabore, Brice Wendlassida ; Peters, Bernhard Scientific Conference (2017, September 27) Impacting particles or static aggregated particles at high temperature may undergo a permanent change of shape modifying the microstructure. Two particles in contact can develop some bonds within sub ... [more ▼] Impacting particles or static aggregated particles at high temperature may undergo a permanent change of shape modifying the microstructure. Two particles in contact can develop some bonds within sub-second time. This fast sintering force in the particular case of the snow contribute to the rheological behavior and grain rearrangement [1]. Understanding the kinetics of sintering in granular material is of great importance in some engineering applications. For decades, diffusional processes have received more attention in investigations related to the mechanisms behind sintering [2]. Some works have suggested that the plastic flow might be neglected in sintering process for stresses are not high enough to cause dislocation. However, some studies have showed that stresses experienced in fine particles necks can be high enough and even lead to plasticity driven sintering. The importance of each mechanism in the sintering process may lie in the temporal and spatial scale of interest. Increasing importance is being accorded to the role of plastic flow in sintering. however, several investigations have proved that the conventional plasticity theory may fail to predict plastic activity at micro-scale, The objective of this work is to develop adequate computational model that includes instantaneous and time-dependent plastic flow at micro-scale. We aim at extending existing models of sintering and plasticity to cope with multiple spatial and temporal scales simulations using Extended Discrete Element Method. The numerical results are compare to experimental data on snow. [less ▲] Detailed reference viewed: 170 (20 UL)Dynamic Sintering of a High Temperature Granular Material: Experiments and Simulations ; Kabore, Brice Wendlassida ; et al Scientific Conference (2017, September 26) Snow changes from a porous solid to a granular material during deformation with high strain rates. This transition occurs in many cases where snow is relevant to engineering problems (vehicle mobility ... [more ▼] Snow changes from a porous solid to a granular material during deformation with high strain rates. This transition occurs in many cases where snow is relevant to engineering problems (vehicle mobility, avalanche formation and prevention, skiing etc.). For the description of the fast deformation of snow the discrete element method (DEM) is a valuable tool, as it is able to account for both states and the transition between them: the interaction of the loose and bonded particles. For the development of a physically relevant DEM snow model [1] we investigate experimentally along with simulations the basic processes of the granular behavior of snow. In the granular state, sintering plays an important role for the dynamics of the particles. Via sintering the high temperature ice particles (homologous temperature 0.95) bond together and change the structure and the physical properties of the material. This temperature dependent sintering process, which happens in the time range of milliseconds to hours, is in the focus of the present work. The fast sintering of ice in the range of milliseconds has scarcely been investigated. However, from sintering studies with ice cones (radius of 3 mm) we know, that the sintering force is closely related to the contact area of the particles [2]. As the contact area changes considerably for complicated shapes, exhibited by natural snow crystals, we consider different snow types (grain shape and size), besides ice beads as spherical model snow. The latter one is used to exclude shape effects and to directly compare experiments to simulations with spherical particles. To be able to take the effects of the grain shape into account and to examine sintering in the time range of interest (seconds), we perform angle of repose experiments and simulations. Snow is sieved to pile up on a flat base until an angle of equilibrium, the angle of repose, is formed. This angle increases with the sintering of the particles, but also with the inter-particle friction. To analyze the contribution of the friction and the grain shape without sintering, we perform the experiments at a low temperature °C ( 0.87), where sintering can be neglected; thus, the angle of repose is determined by inter-particle friction. With these measurements, we calibrate the simulations. At higher temperatures (up to °C) sintering changes the angle of repose, and a physically relevant sintering law for real snow is established in the simulations. [less ▲] Detailed reference viewed: 40 (6 UL)Preliminary investigation on the capability of eXtended Discrete Element method for treating the dripping zone of a blast furnace Baniasadi, Maryam ; Peters, Bernhard in ISIJ International (2017), 58(1), The role of molten iron and slag in the dripping zone of a blast furnace is very critical to reach a stable operational condition. The existence of several fluid phases and solid particles in the dripping ... [more ▼] The role of molten iron and slag in the dripping zone of a blast furnace is very critical to reach a stable operational condition. The existence of several fluid phases and solid particles in the dripping zone of a blast furnace, makes the newly developed eXteneded Discrete Element Method (XDEM) as an Eulerian-Lagrangian approach, suitable to resolve the dripping zone of a blast furnace. In the proposed model, the fluid phases are treated by Computational Fluid Dynamics (CFD) while the solid particles are solved by Discrete Element Method (DEM). These two methods are coupled via momentum, heat and mass exchanges. The main focus of current study is to investigate the influence of packed properties such as porosity and particle diameters, calculated by the XDEM, on the fluid phases for isothermal. In order to present the capability of the XDEM for this application. The validity of the proposed model is demonstrated by comparing model prediction results with the available experimental data. [less ▲] Detailed reference viewed: 119 (8 UL)Parallelizing XDEM: Load-balancing policies and efficiency, a study Rousset, Alban ; Besseron, Xavier ; Peters, Bernhard Scientific Conference (2017, September) In XDEM, the simulation domain is geometrically decomposed in regular fixed-size cells that are used to distribute the workload between the processes. The role of the partitioning algorithm is to ... [more ▼] In XDEM, the simulation domain is geometrically decomposed in regular fixed-size cells that are used to distribute the workload between the processes. The role of the partitioning algorithm is to distribute the cells among all the processes in order to balance the workload. To accomplish this task, the partitioning algorithm relies on a computing/communication cost that has been estimated for each cell. A proper estimation of these costs is fundamental to obtain pertinent results during this phase. The study in the work is twofold. First, we integrate five partitioning algorithms (ORB, RCB, RIB, kway and PhG) in the XDEM framework [1]. Most of these algorithms are implemented within the Zoltan library [2], a parallel framework for partitioning and ordering problems. Secondly, we propose different policies to estimate the computing cost and communication cost of the different cells composing the simulation domain. Then, we present an experimental evaluation and a performance comparison of these partitioning algorithms and cost-estimation policies on a large scale parallel execution of XDEM running on the HPC platform of the University of Luxembourg. Finally, after explaining the pros and cons of each partitioning algorithms and cost-estimation policies, we discuss on the best choices to adopt depending on the simulation case. [less ▲] Detailed reference viewed: 124 (21 UL)Conversion analysis of a cylindrical biomass particle with a DEM-CFD coupling approach Mohseni, Mohammad ; Peters, Bernhard ; Baniasadi, Mehdi in Case Studies in Thermal Engineering (2017), 10 Detailed reference viewed: 101 (7 UL)On the performance of an overlapping-domain parallelization strategy for Eulerian-Lagrangian Multiphysics software Pozzetti, Gabriele ; Besseron, Xavier ; Rousset, Alban et al in AIP Conference Proceedings ICNAAM 2017 (2017, September) In this work, a strategy for the parallelization of a two-way CFD-DEM coupling is investigated. It consists on adopting balanced overlapping partitions for the CFD and the DEM domains, that aims to reduce ... [more ▼] In this work, a strategy for the parallelization of a two-way CFD-DEM coupling is investigated. It consists on adopting balanced overlapping partitions for the CFD and the DEM domains, that aims to reduce the memory consumption and inter-process communication between CFD and DEM. Two benchmarks are proposed to assess the consistency and scalability of this approach, coupled execution on 252 cores shows that less than 1\% of time is used to perform inter-physics data exchange. [less ▲] Detailed reference viewed: 238 (63 UL)Comparing Broad-Phase Interaction Detection Algorithms for Multiphysics DEM Applications Rousset, Alban ; Mainassara Chekaraou, Abdoul Wahid ; Liao, Yu-Chung et al in AIP Conference Proceedings ICNAAM 2017 (2017, September) Collision detection is an ongoing source of research and optimization in many fields including video-games and numerical simulations [6, 7, 8]. The goal of collision detection is to report a geometric ... [more ▼] Collision detection is an ongoing source of research and optimization in many fields including video-games and numerical simulations [6, 7, 8]. The goal of collision detection is to report a geometric contact when it is about to occur or has actually occurred. Unfortunately, detailed and exact collision detection for large amounts of objects represent an immense amount of computations, naively n 2 operation with n being the number of objects [9]. To avoid and reduce these expensive computations, the collision detection is decomposed in two phases as it shown on Figure 1: the Broad-Phase and the Narrow-Phase. In this paper, we focus on Broad-Phase algorithm in a large dynamic three-dimensional environment. We studied two kinds of Broad-Phase algorithms: spatial partitioning and spatial sorting. Spatial partitioning techniques operate by dividing space into a number of regions that can be quickly tested against each object. Two types of spatial partitioning will be considered: grids and trees. The grid-based algorithms consist of a spatial partitioning processing by dividing space into regions and testing if objects overlap the same region of space. And this reduces the number of pairwise to test. The tree-based algorithms use a tree structure where each node spans a particular space area. This reduces the pairwise checking cost because only tree leaves are checked. The spatial sorting based algorithm consists of a sorted spatial ordering of objects. Axis-Aligned Bounding Boxes (AABBs) are projected onto x, y and z axes and put into sorted lists. By sorting projection onto axes, two objects collide if and only if they collide on the three axes. This axis sorting reduces the number of pairwise to tested by reducing the number of tests to perform to only pairs which collide on at least one axis. For this study, ten different Broad-Phase collision detection algorithms or framework have been considered. The Bullet [6], CGAL [10, 11] frameworks have been used. Concerning the implemented algorithms most of them come from papers or given implementation. [less ▲] Detailed reference viewed: 300 (58 UL)Flow characteristics of metallic powder grains for additive manufacturing Peters, Bernhard ; Pozzetti, Gabriele in EPJ Web of Conferences (2017), 13001 Directed energy deposition technologies for additive manufacturing such as laser selective melting (SLM) or electron beam melting (EBM) is a fast growing technique mainly due to its flexibility in product ... [more ▼] Directed energy deposition technologies for additive manufacturing such as laser selective melting (SLM) or electron beam melting (EBM) is a fast growing technique mainly due to its flexibility in product de- sign. However, the process is a complex interaction of multi-physics on multiple length scales that are still not entirely understood. A particular challenging task are the flow characteristics of metallic powder ejected as jets from a nozzle and shielded by an inert turbulent gas flow. Therefore, the objective is to describe numerically the complex interaction between turbulent flow and powder grains. In order to include both several physical processes and length scales an Euler-Lagrange technology is applied. Within this framework powder is treated by the Discrete-Element-Method, while gas flow is described by Euler approaches as found in classical Compu- tational Fluid Dynamics (CFD). The described method succeeded in delivering more accuracy and consistency than a standard approach based on the volume averaging technique and therefore, is suited for the solution of problems within an engineering framework. [less ▲] Detailed reference viewed: 257 (41 UL)Model Study of Multiphase Flow Through Packed Particles by eXtended Discrete Element Method (XDEM) Baniasadi, Maryam ; Peters, Bernhard ; Baniasadi, Mehdi Scientific Conference (2017, June 20) Detailed reference viewed: 104 (14 UL)Investigating Multiphase flow Behavior in Trickle Bed Reactors using eXtended Discrete Element Method (XDEM) Baniasadi, Maryam ; Peters, Bernhard Scientific Conference (2017, May 08) The existence of multiphase flows through packed bed of solid particles in broad spectrum of engineering disciplines such as chemical industries, petroleum engineering, wastewater treatment is undeniable ... [more ▼] The existence of multiphase flows through packed bed of solid particles in broad spectrum of engineering disciplines such as chemical industries, petroleum engineering, wastewater treatment is undeniable. One frequently used reactor of this type is a trickle bed reactor that usually contains particulate phase of which the interstitial space is filled with gas and liquid phases. Based on the direction of the fluid flow they can be classified as cocurrent downflow trickle bed reactors, counter-current trickle bed reactors and cocurrent upflow packed bubble reactors. In these kind of problems numerical simulations can help to gain a better process understanding. In the current distribution, a numerical method so called Extended Discrete Element Method (XDEM) was applied to model multiphase flow through packed bed of solid particles which has the ability to be coupled to Computational Fluid Dynamics (CFD) through interphase momentum transfer. In this coupled solver the fluid phases are treated by CFD while the position and orientation of the particles in each CFD cell and the porosity distribution through packed bed are provided by XDEM. In order to validate the code, two important hydrodynamic parameters such as pressure drop and liquid hold up were investigated and satisfactory agreement between predicted and experimental data was achieved. The model results demonstrate enormous effect of solid particles on the deviation of fluid phases while passing through packed bed by investigating parameters such as velocity and drag force. [less ▲] Detailed reference viewed: 136 (15 UL)Multiscale-multiphysics approaches for engineering applications Pozzetti, Gabriele ; Peters, Bernhard in AIP Conference Proceedings (2017), 1863(1), 180001 Detailed reference viewed: 122 (14 UL)On the choice of a phase interchange strategy for a multiscale DEM-VOF Method Pozzetti, Gabriele ; Peters, Bernhard in AIP Conference Proceedings (2017), 1863 In this work a novel Multiscale DEM-VOF method is adopted to study three phase flows. It consists in solving the fluid momentum, mass conservation and the phase advection at a different scale with respect ... [more ▼] In this work a novel Multiscale DEM-VOF method is adopted to study three phase flows. It consists in solving the fluid momentum, mass conservation and the phase advection at a different scale with respect to the fluid-particle coupling problem. This allows the VOF scheme to resolve smaller fluid structures than a classic DEM-VOF method, and opens the possibility of adopting different volume interchange techniques. Two different volume interchange techniques are here described and compared with reference to high and low particle concentration scenarios. Considerations about the respective computational costs are also proposed. [less ▲] Detailed reference viewed: 326 (49 UL)Comparison of Several RANS Modelling for the Pavia TRIGA Mark II Research Reactor ; Baroli, Davide ; Peters, Bernhard Poster (2017) In this study, a detailed analysis of the turbulent regime within the core of the Pavia TRIGA Mark II reactor is perfomed by means of an in-depth comparison of the RAS (Reynolds-Averaged Simulation ... [more ▼] In this study, a detailed analysis of the turbulent regime within the core of the Pavia TRIGA Mark II reactor is perfomed by means of an in-depth comparison of the RAS (Reynolds-Averaged Simulation) turbulence models implemented in OpenFOAM. Aim of this analysis is to give some important information with respect to the flow regime within the core. The performance of the various models is tested against a LES (Large Eddy Simulation) of the innermost channel. [less ▲] Detailed reference viewed: 53 (2 UL)Evaluating Erosion Patterns in an abrasive water jet cutting nozzle using XDEM Pozzetti, Gabriele ; Peters, Bernhard in Advances in Powder Metallurgy & Particulate Materials (2017) The objective of this work is to analyze particle-induced erosion within a nozzle for abrasive water jet cutting, through a Euler-Lagrange approach. In an abrasive water jet cutting device a high-speed ... [more ▼] The objective of this work is to analyze particle-induced erosion within a nozzle for abrasive water jet cutting, through a Euler-Lagrange approach. In an abrasive water jet cutting device a high-speed water jet is used to accelerate abrasive particles forming a turbulent mixture of water, entrained air and abrasive powders traveling at hundreds of meters per second. The focusing tube represents a key component, whose primary scope is to focus and stabilize the flow forming in the mixing chamber, in order to ensure optimal cutting performances of the device. Nevertheless, this nozzle often happens to be the first target of the erosive action of the flow. This phenomenon significantly shortens the operational life of a nozzle. The numerical approach proposed in this work aims to provide an insight to this very fast and disruptive phenomena that are difficult and expensive to be captured by purely experimental studies. [less ▲] Detailed reference viewed: 326 (49 UL)LES-VOF SIMULATIONS OF A PURE WATER JET DEVELOPING INSIDE AN AWJC NOZZLE: PRELIMINARY OBSERVATIONS AND GUIDELINES Pozzetti, Gabriele ; Peters, Bernhard in Proceedings of 2017 WJTA-IMCA (2017) In this work, a numerical approach to predict the behavior of a pure water jet developing inside a nozzle for Abrasive Water Jet Cutting (AWJC) is investigated. In a standard AWJC configuration, the water ... [more ▼] In this work, a numerical approach to predict the behavior of a pure water jet developing inside a nozzle for Abrasive Water Jet Cutting (AWJC) is investigated. In a standard AWJC configuration, the water jet carries the major energy content of the entire system, and is responsible for accelerating abrasive particles that will perform the cutting action of hard materials. Therefore an accurate simulation of a pure water jet can bring significant insight on the overall AWJC process. Capturing the behavior of a multiphase high-speed flow in a complex geometry is however particularly challenging. In this work, we adopt a combined approach based on the Volume of Fluid (VOF) and Large Eddy Simulation (LES) techniques in order to respectively capture the water/air interface and to model turbulent structures of the flow. The aim of this contribution is to investigate how the two techniques apply to the specific problem, and to offer general guidelines for practitioners willing to adopt them. Costs considerations will be then presented with particular reference to the usage of the OpenFOAM® environment. The reported results are meant to provide guidance for AWJ applications and future developments of AWJ nozzles. [less ▲] Detailed reference viewed: 118 (13 UL)Application of the extended discrete element method (XDEM) in the melting of a single particle Baniasadi, Mehdi ; Baniasadi, Maryam ; Peters, Bernhard in Baniasadi, Mehdi (Ed.) Application of the extended discrete element method (XDEM) in the melting of a single particle (2016, July 19) In this contribution, a new method referred to as Extended Discrete Element Method (XDEM) is usedto model melting of a single particle in the fluid media. The XDEM as a Lagrangian-Eulerian framework is ... [more ▼] In this contribution, a new method referred to as Extended Discrete Element Method (XDEM) is usedto model melting of a single particle in the fluid media. The XDEM as a Lagrangian-Eulerian framework is the extension of Discrete Element Method (DEM) by considering thermodynamic state such as temperature distribution and is able to link with Computational Fluid Dynamics (CFD) for fluid phase. In order to provide more accurate results, multiscale method was used. The model is validated by comparing predicted results with existing experimental data for melting of a single ice particle in a water bath. In addition, the model has the capability to be extended to the packed bed of particles with different size and properties to produce different liquid phases. [less ▲] Detailed reference viewed: 140 (25 UL)ON THE INFLUENCE OF DIFFERENT MAPPING TECHNIQUES FOR A MULTISCALE APPROACH TO TURBULENT THREE-PHASE FLOWS Pozzetti, Gabriele ; Peters, Bernhard Scientific Conference (2016, June 06) In this work we investigate a multiscale approach for high Stokes number, turbulent three phase flows. It is widely proven that a straightforward application of Galerkin's method to problems characterized ... [more ▼] In this work we investigate a multiscale approach for high Stokes number, turbulent three phase flows. It is widely proven that a straightforward application of Galerkin's method to problems characterized by multiscale phenomena does not generally lead to robust numerical solutions. In this optic, multiscale methods are commonly adopted in order to provide solutions for complex problems in an highly efficient way. In certain problems it is convenient to identify multiple scales (more than 2), each characterized by its own characteristic spatial and temporal length. For this kind of problems a possible approach consists in completely resolving the coarse scales, partially resolving the middle scales, while analytically modeling the smallest. In turbulent three phase flows with high Stokes number, those can be identified respectively as the particle characteristic scale, the interface dynamic scale, and the turbulent fine scale. The coarse scale is here resolved through an Eulerian-Lagrangian approach that enables us to track the particle motion in a Lagrangian way. We partially resolve the middle-scale through the usage of a supporting domain where semi local variables are resolved. The solution of the middle-scale is based on the Volume of Fluid (VOF) technique in order to capture the dynamic interface, while turbulent phenomena are solved with a Large Eddy Simulation (LES) approach. The coarse-scale domain and the middle-scale domain must exchange informations and this process is obtained by mapping variables between the two fields. We will here show how the choice of the mapping technique largely affect the solution in therms of both accuracy and efficiency. A thoughtful study about the optimal mapping strategy could therefore be extremely beneficial in order to discover the most suitable scale-linking technique. The aim of this work is to investigate the effect of the adopted mapping technique on the resolved scale. Simulations with different Reynolds and Stokes number are proposed and compared, and conclusions about the consistency of the mapping technique are drawn. [less ▲] Detailed reference viewed: 133 (15 UL)CFD-XDEM FOR PREDICTING MULTIPHASE FLOW BEHAVIOR THROUGH POROUS MEDIA Baniasadi, Maryam ; Peters, Bernhard Scientific Conference (2016, June 05) An accurate description of fluid flow through porous media is very important to predict, design and optimize many industrial phenomena principally in condition where experimental studies are difficult to ... [more ▼] An accurate description of fluid flow through porous media is very important to predict, design and optimize many industrial phenomena principally in condition where experimental studies are difficult to perform. In these kind of problems numerical simulations can help to gain a better process understanding. During last decades many numerical approaches mainly Finite Volume Method (FVM) were applied to model different multiphase flows containing gas, liquid and solid phases. The solid phase may treat by continuous or discrete frameworks. In the former method which is based on Eulerian framework the solid phase is considered as a continuous phase like other fluid phases while in the second method which is based on Lagrangian framework, the solid phase is considered as separate particles. In this study, the flow behavior of several incompressible isotherm phases through solid particles was modelled. The model describes the motion of fluid flows such as gas and liquid phases using continuum approach by applying Computational Fluid Dynamics (CFD) as a numerical method and the solid particles by Lagrangian framework using so-called eXtended Discrete Element Method (XDEM). XDEM is a numerical simulation framework based on classical Discrete Element Methods (DEM) extended by consideration of thermophysical states. A combination of the two numerical methods was performed through momentum and mass exchange between fluid and solid phases which is called combined continuum discrete approach. The solid phase is considered as packed solid particles. The model results demonstrate enormous effect of solid particles on deviation of fluid phases while passing through particles by testing different drag force models. This model was applied to the dripping zone of blast furnace where the liquid phases of liquid iron and slag flow downward through coke particles and gas phase ascends upwards through the shaft which is classified as a counter-current multiphase packed bed reactor. The main goal of this project is to provide a solver which is able to treat several fluid phases through porous media using combined Eulerian-Lagrangian framework by exchanging data between this two approaches. [less ▲] Detailed reference viewed: 104 (7 UL)A DEM-LES-VOF METHOD FOR TURBULENT THREE PHASE FLOWS Pozzetti, Gabriele ; Peters, Bernhard Scientific Conference (2016, May 26) In this work a robust Computational Fluid Dynamic (CFD) - Discrete Element Method(DEM) coupling that can predict free-surface, turbulent flows is presented. A correct prediction of multiphase turbulent ... [more ▼] In this work a robust Computational Fluid Dynamic (CFD) - Discrete Element Method(DEM) coupling that can predict free-surface, turbulent flows is presented. A correct prediction of multiphase turbulent flows should ideally be able to capture the discrete dynamics of a dispersed phase (solid particles), and at the same time to take into account the evolution of possible fluid-dynamic instabilities. In this optic a CFD-DEM approach seems promising as it is able to combine the well developed CFD techniques for the study of free-surface flows with the accuracy of the Discrete Particle Method(DPM). A key point of the CFD-DEM method is the coupling between the discrete and the continuous phases. In particular the volume replacement between phases, and the interaction between the discrete phase and the continuous interface must be taken into account in order to perform accurate three phase simulations. In this work two different approaches to simulate the volume replacement between phases are presented and compared within a four way coupling with a Large Eddy Simulation(LES)-Volume Of Fluid(VOF) solver. The four-way coupled equations for the solid and the fluids are then presented, and some test cases provided in order to evaluate the accuracy of the new solver. Particular emphasis is posed to study the effects of the coupling on the interface dynamics and stability. The continuous two-phase solver used for the simulations is based on the OpenFoam® architecture, while the discrete phase solver is built on the XDEM code. [less ▲] Detailed reference viewed: 315 (13 UL) |
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