Effect of Discretization of Permeability Term and Mesh Size on Macro- and Meso-segregation Predictions

Macro- and meso-segregations correspond to heterogeneities of composition at the scale of a casting. They develop during the solidification. One of the parameters that has an essential effect on these segregations is the mush permeability which varies over a wide range of magnitude. We present simulation results for solidification of Sn-Pb alloy in a two-dimensional cavity. The role of discretization schemes and mesh size on the formation of channel segregates and macrosegregation is discussed

First analysis of a numerical benchmark for 2D columnar solidification of binary alloys

International audienceDuring the solidification of metal alloys, chemical heterogeneities at the product scale (macrosegregation) develop. Numerical simulation tools are beginning to appear in the industry, however their predictive capabilities are still limited. We present a numerical benchmark exercise treating the performance of models in the prediction of macrosegregation. In a first stage we defined a "minimal" (i.e. maximally simplified) solidification model, describing the coupling of the solidification of a binary alloy and of the transport phenomena (heat, solute transport and fluid flow) that lead to macrosegregation in a fully columnar ingot with a fixed solid phase. This model is solved by four different numerical codes, employing different numerical methods (FVM and FEM) and various solution schemes. We compare the predictions of the evolution of macrosegregation in a small (10×6 cm) ingot of Sn-10wt%Pb alloys. Further, we present the sensitivities concerning the prediction of instabilities leading to banded channel mesosegregations

Contribution à la simulation numérique des procédés à haute température: Développer des outils de recherche pour des applications industrielles

The projects presented in this manuscript are embedded in the numerical simulation of the elaboration processes of materials at high temperature, both ceramics and metals. They have in common the use of numerical tools, in-house or commercial codes (always with adaptation to our problems) in order to simulate, at a macroscopic or mesoscopic scale, an industrial process in which measurements are limited by environmental conditions. Numerical simulation is thus a privileged way to understand the process and optimize the operation of reactors. The following topics are discussed in turn: thermal plasma spraying, the conversion of uranium oxide to tetrafluoride, liquid metal processes (EB melting, ElectroSlag Refining - ESR) and the solidification of metallic alloys.Different papers published in international journals illustrate the main aspects of the models and their use in the context of applied research.The perspectives relate both to the continuation of my current research activities (ESR process), to certain obstacles to be overcome (models of scale and / or dimension change, simulation of the movement of grains or drops and their interactions in a turbulent flow), and opens up new horizons that data mining and artificial intelligence can bring to the design of new materials.Les projets présentés dans ce manuscrit s’inscrivent dans le cadre de la simulation des procédés d’élaboration des matériaux à haute température, aussi bien les céramiques que les métaux. Ils ont en commun l’utilisation des outils numériques, codes « maison » ou commerciaux (toujours avec adaptation à nos problématiques) pour simuler, à l’échelle macroscopique ou mésoscopique, un procédé industriel au sein duquel les mesures sont limitées par les conditions environnementales. La simulation numérique est alors une voie privilégiée pour comprendre le procédé et optimiser la conduite des réacteurs. Sont abordés tour à tour : la projection par plasma thermique, la conversion d’oxyde d’uranium en tétrafluorure, des procédés de traitement du métal liquide (fusion BE, élaboration sous laitier électroconducteur – ESR) et la solidification des alliages métalliques.Des articles publiés dans des revues internationales illustrent les principaux aspects des modèles et leur utilisation dans un cadre de recherche appliquée. Les perspectives portent à la fois sur la continuation de mes recherches actuelles (procédé ESR), sur certains verrous à lever (modèles de changements d’échelle et/ou de dimension, simulation du mouvement de grains ou de gouttes et leurs interactions dans un écoulement turbulent), et s’ouvre sur les nouveaux horizons que peuvent apporter la fouille de données et l’intelligence artificielle dans le cadre de la conception de nouveaux matériaux

Influence of Discretization of Permeability Term and Mesh Size on the Prediction of Channel Segregations

International audienceMacro- and meso-segregations correspond to compositional heterogeneities at the scale of a casting. They develop during the solidification process. One of the parameters that have an essential effect on these segregations is the mush permeability, which is highly nonlinear and varies over a wide range of magnitudes. We present simulation results for solidification of a Sn-Pb alloy in a two-dimensional cavity, highlighting the role of (i) the numerical interpolation schemes used for the finite-volume discretization of the highly-nonlinear permeability term and (ii) of the mesh size on the prediction of mesosegregations and macrosegregation. We observe that solute rich liquid flowing through the mushy zone due to thermsolutal convection results in patches of thin channel structures, which develop into mesosegregations. We notice little sensitivity of the predicted macrosegregation to different discretization schemes for the permeability term. However, we found their influence on the prediction of channel segregates to be significant when using coarse computational grids, customary in the simulation of industrial castings. Mesh refinement is crucial for capturing the complex phenomena in the formation of channel segregates. With a very fine mesh channels have been captured with more than one grid point along their width, allowing the determination of their width. An important conclusion is that a coarse mesh can capture rather well the risk to form channel segregates, but only a fine mesh is able to resolve the complex phenomena involved in more detail

Analysis of the Thermal Transfers in a VASM Crucible: Electron Beam Melting Experiment and Numerical Simulation

A description of the Vacuum Arc Skull Melting (VASM) process is presented showing its particularly complex features because of the mixing of porous raw materials with the dense remelted metal as well as the very high temperature and the highly transient nature of the process. This paper presents a 3D transient mathematical modelling of the heat transport with the aim of bringing a better understanding of the thermal behavior of the material into the crucible during a melting cycle. The model takes into account the heat input provided by the incoming metal thanks to an adaptive meshing, as well as the latent heat of solidification and the radiative heat transfers. An experimental validation of the model is presented where an electron beam heating source mimics the heat effect of the arc thanks to an excellent guidance of the beam over the melt surface. A comparison between the measured and calculated temperatures of a steel load is reported and reveals a satisfactory agreement. With very few adjustments, concerning mainly heat radiation at the top surface of metal into the crucible, the numerical model appears to be an efficient numerical tool to simulate the VASM process at the industrial scale

DNS and engineering modeling of the Electroslag Remelting process

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Coupling of CFD and PBE Calculations to Simulate the Behavior of an Inclusion Population in a Gas-Stirring Ladle

International audienceGas-stirring ladle treatment of liquid metal has been pointed out for a long time as the processing stage is mainly responsible for the inclusion population of specialty steels. A steel ladle is a complex three-phase reactor, where strongly dispersed inclusions are transported by the turbulent liquid metal/bubbles flow. We have coupled a population balance model with CFD in order to simulate the mechanisms of transport, aggregation, flotation, and surface entrapment of inclusions. The simulation results, when applied to an industrial gas-stirring ladle operation, show the efficiency of this modeling approach and allow us to compare the respective roles of these mechanisms on the inclusion removal rate. The comparison with literature reporting data emphasizes the good prediction of deoxidating rate of the ladle. On parallel, a simplified zero-dimensional model has been set-up incorporating the same kinetics law for the aggregation rate and all the removal mechanisms. A particular attention has been paid on the averaging method of the hydrodynamics parameters introduced in the flotation and kinetics kernels

Numerical modeling of heat treatment : fluid flow -thermal -metallurgical -mechanical couplings

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