The introduction of a small amount of flexible fibers into a granular medium is an effective and inexpensive technique to reinforce the mechanical resistance of these materials. Although the way fibers affect the volumic fraction of a mixed of beads and fibers and the way fibers affect the flowing properties of the material is much unknown. To fill this gap, we measure the flowing response of...
Various practical situations involve the movement of several objects in a granular medium, such as animal locomotion or civil engineering applications. In this work, we study the interaction between objects and measure the drag experienced by a pair of spherical intruders moving side-by-side into grains at constant depth and constant velocity. We quantify the influence of the separation...
Upscaling non-equilibrium heat transfer in porous systems is important for many engineering applications where thermal efficiency and temperature distribution need to be predicted. For that purpose, the Volume Averaging method allows to write averaged equations that describe macroscopic heat transfer of inertial flows in porous media.
Here, a study of the Volume Averaging model is proposed...
Shear thickening fluids are liquids that stiffen as the applied stress increases. If many of these types of fluids follow a monotonic rheological curve, some experimental and numerical studies suggest that certain fluids, like cornstarch, may exhibit a non-monotonic, S-shaped rheology. In this work, we experimentally and numerically study the implications of such rheology for the simple...
Liquid/vapour water flows are encountered in several fields, such as in Proton Exchange Membrane Fuel Cell (PEMFC), a promising technology to electrify the energy system. In PEMFC, electricity is produced by recombining oxygen and hydrogen fed via gas channels. Water is also generated and should be evacuated via the channels. As the temperature is low (60-80°C), water is observed both as...
We analyze the dynamics of two layers of immiscible, inviscid, incompressible, and irrotational fluids through a full nonlinear system. Our goal is to establish a virial theorem and prove the polynomial growth of slope and curvature of the interface over time when the fluid below is no denser than the one above. These phenomena, known as Rayleigh-Taylor instability and Kelvin-Helmholtz...
We study the modal (self-excited) and non-modal (amplifier) dynamics of a mean turbulent separation bubble (TSB) forming over a flat plate via an artificial adverse pressure gradient. The flow configuration is in direct comparison to recent DNS and experimental studies. We reconstruct the two-dimensional turbulent mean-flow using the Reynolds-Averaged Navier Stokes (RANS) equations closed with...
Rotor-stator flows are known to exhibit instabilities in the form of circular and spiral rolls. While the spirals are known to emanate from a supercritical Hopf bifurcation, the origin of the circular rolls is still unclear. A quantitative scenario for the circular rolls as a response of the system to external forcing is suggested. Two types of axisymmetric forcing are considered: bulk...
Complex phenomena, such as turbulence, require the use of laborious and resource-intensive algorithms. This incurs significant costs in terms of storage space and computation time. Machine and deep learning techniques are introduced to tackle such challenges, offering solutions such as reduced models, simulation acceleration, and data compression.
Physics-Informed Neural Networks (PINNs)...
The Particle Finite Element method is a fluid solver based on Lagrangian finite elements combined with efficient re-meshing algorithms. It was shown to be effective in a large amount of applications, especially in the case of free surface fluids flows or fluid-structure interactions. Up to now, this method has never been paired up with any model-order reduction technique because of the...
L'écoulement de von Kármán, étudié depuis les années 1990, est devenu un système canonique dans l'étude de la turbulence. L'écoulement est produit par deux turbines entrainant un fluide dans un cylindre fermé, et permet expérimentalement d'atteindre des nombres de Reynolds élevés efficacement. Muni de données LES 3D à Re ≈ 50 000 issu du code SFEMaNS, on détaillera les structures principales...
Pour améliorer la portée d’un obus, on ajoute à son culot un chargement de propergol solide (base-bleed) qui, lorsqu’il brûle, génère un écoulement dans le sillage de l’obus lors de la phase de balistique extérieure. Cet écoulement modifie la recirculation au culot de l’obus, ce qui réduit sa trainée. Lorsque l’obus sort du canon (balistique intermédiaire), une importante dépressurisation des...
Active particles are inherently out-of-equilibrium systems, able to uptake energy from their environment and convert it to motion.
For example, Chlamydomonas Reinhardtii (CR) is a micro-swimmer whose orientation can be dictated by a light gradient in its environment (phototaxis). It is known that a collective motion triggered due to the phototaxis of a population of CR generates a nonlinear...
Diatoms are among the most abundant microorganisms found in both oceanic and freshwater environments worldwide. While some species drift passively with ambient currents, others employ various strategies for movement or self-propulsion. One species in particular, called Bacillaria Paxillifer, forms colonies of stacked rectangular cells that slide along each other while remaining parallel. This...
Séparer les bactéries d'un fluide pour les trier, les concentrer ou assainir est un enjeu crucial dans les domaines de la santé et de la microbiologie. Notre étude démontre que le couplage entre l'écoulement du fluide et le mouvement des bactéries (la rhéotaxie), qui génère un flux transversal à l'écoulement, peut être utilisé pour accomplir ces opérations. Afin de garantir un contrôle optimal...
La rhéologie des suspensions denses de particules a été principalement étudiée dans des configurations de cisaillement simple. La validité de ces résultats pour prédire l'écoulement de suspensions dans des configurations plus complexes reste à établir. Dans ce contexte, nous étudions expérimentalement la dynamique d'une sphère qui sédimente dans une suspension et s'approche d'une paroi...
Turbulent convection is a spontaneous physical process in natural environments and many industrial systems. However, most of these systems are not ideal in terms of underlying surfaces and involve specific topography or small-scale roughness. Interactions between plate roughness and nearby flow can induce changes in turbulence scales [1]. In addition, when the side walls of a cavity confine...
Il est depuis longtemps proposé que la dynamique océanique à petite échelle est pilotée par celle des ondes internes de gravité. Décrire physiquement ces petites échelles, qui ne sont pas résolues dans les modèles océaniques, constituerait un levier majeur d'amélioration des paramétrisations dans les simulations du climat. Dans ce contexte, la théorie la plus prometteuse est celle de la...
Nous présentons ici les différentes formes de vagues pouvant être générées par le mouvement impulsionnel d’un piston dans un canal, en variant la vitesse du piston et sa course, ainsi que la hauteur d’eau. Nous nous intéressons en particulier aux premiers instants de formation du bourrelet d’eau induit par l’avancée du piston, tant en amplitude qu'en forme. A faible accélération du piston, une...
In this study, we perform two-dimensional, axisymmetric simulations to investigate the growth and departure of a single bubble, with a particular focus on the conjugate heat transfer between the fluid and the heating wall. A multiscale modeling approach is employed to account for nanoscale effects near the liquid-vapor-solid triple contact line (CL). At the macro scale, the interface dynamics...
The study of boiling flow is of considerable interest as it plays a crucial role in optimizing thermal performance in various industrial scenarios. Diverse approaches have been proposed to simulate nucleate boiling in the framework of the interface tracking method. However, accurately predicting boiling heat transfer remains challenging due to the involvement of multiscale phenomena. To better...
Multiphase flows interacting with complex solid geometries are challenging and difficult to tackle either experimentally or numerically because of the complexity of the flow coupled with generally heterogeneous solid structures. When phase change is involved, such as in solidification in ice formation, this can be even more complex.
A non trivial coupling of the Volume Of Fluid approach to...
We present numerical results of the simulation of a multicomponent droplet in water. Due to diffusion the mass density of the initially light droplet increases. As a result after an initial ascencion the droplet starts to fall.
Here we show that the interplay between diffusion and flow leads to unexpected effects that affect significantly the motion of the droplet.
La solidification lors d’impact de goutte sur différents substrats permet d’accéder à une large variété de morphologies.
L’utilisation d’un substrat liquide amène à considérer son épaisseur et la combinaison des paramètres physiques de la goutte et du substrat.
Nous présentons ici une étude expérimentale sur la solidification de gouttes d'alcane impactant un bain d’eau salée.
Les gouttes...
When a liquid drop impacts onto a cold enough substrate, a complex interplay occurs between phase change and the spreading dynamics of the liquid film. A better understanding of this configuration has potentially a broad scope of applications, ranging from three-dimensional printing or metallurgy to aircraft icing problematics. In the present paper, we report experiments of water drop impacts...
Si un jet liquide entre dans un bain liquide avec une rugosité ou une vitesse suffisante, il peut entraîner de l'air sous forme de bulles. Si des surfactants sont présents dans la solution, ces bulles seront suffisamment stables pour former une couche de mousse à la surface. Le jet va alors interagir avec cette couche de mousse. Pour étudier cette situation, nous avons réalisé des cuves quasi...
Spray are more effective in dissipating heat compared to forced air convection. However, in heat exchangers, there is one drawback: harmful water films can obstruct the airflow through the fins during spray injection. Consequently, the study investigates the clogging processes related to water films generated by the spray.
Numerical methods using the Volume Of Fluid (VOF) approach...
Recent studies of transonic flows around airfoil have shown, that shock unsteadiness at low frequencies is significantly influenced by the presence of laminar flow regions. The low frequency shock motion called buffet is particularly dangerous, since it induces large lift oscillations, which can provoke an aeroelastic buffeting instability. The present work aims at investigating the onset of...
Dans le cadre du projet ANR « du Carbone à l’or olympique » nous travaillons avec la Fédération Française de Voile pour les Jeux Olympiques de cet été. Lors de cet événement la moitié des épreuves de voile auront lieu sur des engins sortant de l’eau grâce à des foils, ce qui est nouveau et ouvre des perspectives stimulantes du point de vue de la mécanique des fluides. Comme exemple, je...
Le mouvement d’objets flottants à la surface de vagues est étudié depuis longtemps car il possède plusieurs applications à la fois dans des domaines d’ingénierie navale ou environnementales. Nous avons observé dans un canal à houle que des flotteurs flexibles dérivent et se réorientent au gré des vagues dans une direction préférentielle, parallèle à la direction de propagation de l’onde. Cette...
Turbulence is ubiquitous in nature. The choice of the theoretical model is particularly important because of its multiscale character. The energy is injected at large scales, coupling phenomena occur at meso-scales, and it is finally dissipated at micro-scales. Kinetic codes include all the physics but they are too heavy to produce simulations in reasonable times. Thus, reduced models are...
Air-in-liquid compound drops can be used to produce foam materials or for the fabrication of Thermal Barrier Coatings. The impact of these compound drops can finally leave an encapsulated bubble onto the target surface, or a thin liquid film, depending the eventual bursting of the bubble. The presence of the bubble in the drop affects the impact dynamics, leading to the formation of a counter...
