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Analyse des effets des singularités induites par le procédé AFP au sein d'éprouvettes pleines et trouées en compression par dialogue essai/calcul
No full textInternational audienceThe AFP process induces unavoidable singularities such as gaps and overlaps. When singularities areplaced within coupons made of continuous carbon fibres impregnated with a thermoset matrix, thefailure properties under compression are modified. Experimental tests results are difficult to analysebecause of coupling effects that are probably due to structural effects that are difficult to characterisedespite a rich multi-instrumentation. To better understand the test results, an approach based on adialogue between the test results and the numerical simulations is developed. The method allows tocompare several meshed geometries and ply material laws in order to define the level of modellingdetails required to simulate the effects of singularities.Le procédé AFP induit inévitablement des singularités de type gaps et overlaps. Lorsque cessingularités sont placées au sein d’éprouvettes en fibres de carbone continues imprégnées de matricethermodurcissable, les propriétés à rupture en compression sont modifiées. Les essais expérimentauxde compression sont complexes à interpréter en raison de phénomènes de couplage liés à des effetsde structures difficiles à caractériser malgré une instrumentation riche. Pour aider à l’exploitation desdonnées d’essais, une démarche de dialogue essai-calcul est mise en place afin de simulernumériquement les essais. La démarche permet de comparer plusieurs géométries maillées et lois decomportement du pli afin de définir le niveau de détail de modélisation nécessaire pour simuler leseffets des singularités
Multi-class local time-stepping strategy for multi-methods/ multi-domains schemes to solve time domain Maxwell's equations
No full textInternational audienceIn this article, we propose a local time-stepping strategy adapted to a multi-domain/multi-method approach. This approach allows the initial computational domain to be divided into sub-domains in which a specific solver is defined. Each solver has its own time-step parameters, which are therefore not necessarily identical. In this process, each solver must exchange data at a given time. To have identical times on each solver, it is then necessary to coordinate each local time-stepping present in each solver in order to have a time coherence at the scale of the whole simulation. After introducing the principle of the strategy employed, we illustrate its performances by coupling structured and unstructured finite volume solvers
Fabrication and characterization of a streamlined micro hot wire probe to reduce aerodynamic disturbances
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A numerical investigation on the flow effect over the Nusselt number in single droplet combustion
No full textInternational audienceNumerical simulations of the combustion of isolated droplets, based on an interface capturing two-phase flow solver, are presented in this paper. The new numerical solver used is an extension of a classical evaporation solver based on a Level Set-Ghost Fluid Method to combustion applications. It is based on a variable density low Mach number solver for Navier–Stokes equations, and it accounts for complex thermo-physical variations of physical properties. After presenting a preliminary validation against experimental data for a n-decane static burning droplet, it is shown that the numerical simulations reproduce accurately different types of flame shapes. In particular, depending on the conditions, an envelope flame surrounding the droplet, a wake flame attached at the rear of the droplet or side flame, which is an intermediate state between the previous two regimes, are observed. The numerical results clearly demonstrate the strong effect of the different flame shapes on the Nusselt number of the evaporating droplet. The Nusselt number tends to decrease during the transition between the envelope flame to the wake flame, exhibiting a non-monotonic behavior for increasing Reynolds numbers. These results are significant since classical correlations on the Nusselt number assumes a monotonic increase for increasing Reynolds numbers, and thus miss the effect of the transition between the envelope flame to the wake flame. Finally, the solver developed for the sake of this study, presents many potentialities to explore more complex configurations than isolated and spherical droplets. Indeed, the overall numerical methodology enables to handle any interface shape and topology, and can be relevant to study collective effects, as the combustion of droplet groups, for instance
Métasurface à modulation temporelle pour des applications antennaires
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Méthodes de reconstruction de gradient robustes et précises pour les schémas volumes finis centrés aux cellules sur maillages anisotropes
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Modélisation de la turbulence pour les équations RANS compressibles assistée par inversion de champ et apprentissage automatique
No full textInternational audienceThis work presents a field-inversion (FI) and machine learning (ML)-augmented turbulence closure model for Reynolds-averaged Navier-Stokes (RANS) equations, targeting shock-wave/turbulent boundarylayer interaction (SWTBLI) flows. A database of optimal corrections is generated via adjoint-based FI across representative SWTBLI configurations. An artificial neural network (ANN) is then trained to regress these corrections for unseen cases.Special emphasis is placed on input feature design and on the training loss definition: rotational and Galilean invariances are enforced, and a hybrid local/non-local damping function ensures smooth transitions at turbulent/non-turbulent interfaces. The ANN is trained with a custom loss function that promotes robustness and invariance to noisy inputs.The database is used to perform both interpolation and extrapolation scenarios, enabling a comprehensive assessment of the ANN's capabilities and limitations. Full exploitation of the available data ensures that the resulting FI-ML augmented model improves turbulence closure across weakly to strongly separated SWTBLI flows, yielding enhanced predictions of the interaction zone and accurate boundary-layer resolution in both interpolative and extrapolative regimes.Ce travail présente un modèle de fermeture de turbulence pour les équations de Navier-Stokes moyennées à la Reynolds (RANS), assisté par inversion de champ (FI) et apprentissage automatique (ML), spécifiquement conçu pour les écoulements d'interaction onde de choc/couche limite turbulente (SWTBLI). Une base de données de corrections optimales est générée via une inversion de champ basée sur un adjoint, appliquée à des configurations représentatives de SWTBLI. Un réseau neuronal artificiel (ANN) est ensuite entraîné pour régresser ces corrections dans des cas non encore vus.Une attention particulière est portée à la conception des caractéristiques d'entrée et à la définition de la fonction de coût d'apprentissage : l'invariance rotationnelle et galiléenne sont imposées, et une fonction d'amortissement hybride locale/non-locale garantit des transitions fluides aux interfaces turbulentes/non-turbulentes. Le ANN est entraîné avec une fonction de coût modifiée qui favorise la robustesse et l'invariance face à des entrées bruyantes.La base de données est variée pour inclure à la fois des scénarios d'interpolation et d'extrapolation, permettant ainsi une évaluation complète des capacités et des limites du modèle FI-ML augmenté. L'exploitation exhaustive des données disponibles garantit que le modèle résultant améliore la fermeture de turbulence pour les écoulements SWTBLI faiblement à fortement séparés, conduisant à des prédictions améliorées de la zone d'interaction et à une résolution précise de la couche limite dans les régimes à la fois interpolatif et extrapolatif
Effet des conditions d'entrée turbulentes sur la dynamique de l'écoulement asymétrique d'une cavité supersonique 3D
No full textInternational audienceA supersonic three-dimensional open cavity, of naturally asymmetric flow, has been studied by means of a hybrid RANS/LES method (ZDES mode 2 (2020)) and a WMLES approach (ZDES mode 3). For the latter, turbulent inflow conditions representative of wall-bounded turbulence have been rapidly obtained thanks to a dynamic forcing method extended to compressible flows. Both simulations have been validated against experimental data and their in-depth analysis has been performed. In particular, besides the mean flow, spectral analysis of the turbulent field has been carried out in order to better assess the effect of realistic turbulent fluctuations on these kind of flows. The results suggest that the dynamics of the cavity dominate over those of the incoming turbulent boundary layer, but some small effects are still observed. Besides, the asymmetric feature has also been explored by means of the spectral POD (SPOD) analysis the velocity field
CSiPI : a numerical tool for plasma erosion phenomena in space applications
No full textInternational audienceThe massive, and growing, presence of electric propulsion devices onboard spacecrafts enhances the importance of plasma erosion phenomena among the space community. In a context lacking extensive experimental databases, numerical modelling represents an attractive solution to estimate plasma sputtering. This work introduces the latest version of CSiPI (Code de Simulation de la Pulvérisation Ionique -Simulation Code for Ion Sputtering), a numerical tool for the characterisation of the material response to the ionic bombardment. Based on the widely-used binary collision approximation, the model is discussed in details. A comprehensive description of its current numerical implementation highlights the main differences from existing models, like the treatment of the binding energies. Validation through comparison with experimental and numerical results proves that the novel version of the software can compute effectively key erosion magnitudes (sputtering yield and angular distribution of eroded particles) of mono-atomic metals and ceramic materials subject to plasma conditions relevant for space applications. Future activities aimed at further improving the code and integrating it with numerical software for space mission simulations are also briefly discussed