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International audience; The mixing of immiscible oil and water by a pitched blade turbine in a cylindrical vessel is studied numerically.Three-dimensional simulations combined with a hybrid front-tracking/level-set method are employed to capturethe complex flow and interfacial dynamics. A large eddy simulation approach, with a Lilly-Smagorinsky model, isemployed to simulate the turbulent two-phase dynamics at large Re = 5663 - 56632. The numerical predictionsare validated against previous experimental work involving single-drop breakup in a stirred vessel. For small Re,the interface is deformed but does not reach the impeller hub, assuming instead the shape of a Newton’s Bucket.As the rotating speed increases, the deforming interface attaches to the impeller hub which leads to the formationof long ligaments that subsequently break up into small droplets. For the largest Re studied, the system dynamicsbecomes extremely complex wherein the creation of ligaments, their breakup, and the coalescence of drops occursimultaneously. The simulation outcomes are presented in terms of spatio-temporal evolution of the interface shapeand vortical structures. The results of a drop size analysis in terms of the evolution of the number of drops, andtheir size distribution, is also presented as a parametric function of Re.

International audience; In this work, we study the effect of insoluble surfactants on the three-dimensional rim-driven retraction dynamics of thin water sheets in air. We employ an interfacetracking/level-set method to ensure the full coupling between the surfactant-induced Marangoni-stresses, interfacial diffusion, and inertia. Our findings are contrasted with the (Newtonian) dynamics of a liquid sheet edge finding that the surfactant concentration can prevent, or delay, the breakup of the rim. Our simulations use the fastest growing Rayleigh-Plateau instability to drive droplet detachment from the fluid sheet (rim). The results of this work unravel the significant role of Marangoni stresses in the retracting sheet dynamics at large elasticity numbers. We study the sensitivity of the dynamics to the elasticity number and the rigidification of the interface.

International audience; The dynamics of ligaments retracting under the action of surface tension occurs in a multitude of natural and industrial applications, such as inkjet printing and atomisation. We perform fully three-dimensional, two-phase direct numerical simulations of the retraction dynamics with soluble surfactants. A full parametric study is performed using a hybrid interface-tracking/level-set method, which is utilised to treat the interface; this method is capable of capturing faithfully the topological transitions that are a feature of the flow over a certain range of ligament aspect ratios and Ohnesorge numbers. Our results demonstrate the delicate interplay between capillarity, modulated by the presence of surfactants, surfactant-induced Marangoni stresses, inertial and viscous effects. Particular attention is paid to the formation of vortices, which accompany the retraction process, and the influence of surfactant on the vortex dynamics.

International audience; We adapt and extend a formulation for soluble surfactant transport in multiphase flows recently presented by Muradoglu & Tryggvason (JCP 274 (2014) 737-757) to the context of the Level Contour Reconstruction Method (Shin et al. IJNMF 60 (2009) 753-778) which is a hybrid method that combines the advantages of the Front-tracking and Level Set methods. Particularly close attention is paid to the formulation and numerical implementation of the surface gradients of surfactant concentration and surface tension. Various benchmark tests are performed to demonstrate the accuracy of different elements of the algorithm. To verify surfactant mass conservation, values for surfactant diffusion along the interface are compared with the exact solution for the problem of uniform expansion of a sphere. The numerical implementation of the discontinuous boundary condition for the source term in the bulk concentration is compared with the approximate solution. Surface tension forces are tested for Marangoni drop translation. Our numerical results for drop deformation in simple shear are compared with experiments and results from previous simulations. All benchmarking tests compare well with existing data thus providing confidence that our adapted LCRM formulation for surfactant advection and diffusion is accurate and effective in three-dimensional multiphase flows. We also demonstrate that this approach applies easily to massively parallel simulations.

The ability to predict the behaviour of multiphase flows accurately, reliably, and efficiently addresses a major challenge of global economic, scientific, and societal importance. These flows are central to virtually every processing and manufacturing technology. Significant advances have been made in the numerical methods to simulate these flows; examples of these include the use of Large Eddy Simulations to simulate turbulence, and interfacecapturing or tracking techniques to deal with the free surface. These codes have made progress in simulating the interaction of a turbulent flow field with an interface, however, there remains a large gap between what is achievable computationally and ‘real-life’ systems. We will present the latest on the modelling framework that we are currently developing within the Multi-scale Examination of MultiPHase physIcs in flowS (MEMPHIS) programme that will enable the use of numerical simulations as a reliable design tool. The framework features Front-Tracking/Level-Set hybrids, an Immersed Boundary approach to Fluid-Structure Interaction and sophisticated multi-scale, multi-physics models. The code we call BLUE is fully parallelised and can run on various platforms: from laptops to supercomputers (on over 250,000 cores). This allows the user the flexibility to choose between a quick ‘answer’ with a degree of uncertainty common to engineering applications or a high-fidelity solution, for targeted cases, that requires more time. BLUE also has builtin, user-friendly meshing capabilities that allow rapid construction of complex geometries. We present a number of simulations of problems of interest to process industries and biomedical applications, which include the design of container-filling processes, two-fluid mixing with a rotating impeller, high-speed atomization, microfluidic droplet encapsulation, falling film reactors featuring non-Newtonian fluids, and surfactant-driven non-isothermal flows.

An analysis of parliamentary debates and media resources that cover them can provide insight into the political climate of a country. Although debates are now regularly published on official government portals, their analysis remains a cumbersome and challenging task for historians and political scientists. One of the main tasks of the PoliMedia project is to allow easy cross-media comparisons and give better insight into choices that different types of media outlets make when covering parliamentary debates. As a first step of that task, Dutch parliamentary debate data available in XML files is being translated into Semantic Web standards, which will allow users to easily query the data. In this paper we discuss design choices we made to build a semantic model that will represent events and topics from the Dutch parliamentary debates.

Colloque avec actes et comité de lecture. Internationale.; International audience; On présente une méthode numérique pour simuler des écoulements diphasiques à phases séparées comportant une phase incompressible (liquide) et une phase faiblement compressible (gaz). On résout les équations de Navier-Stokes, dans une approche faible Mach pour la phase gazeuse, et avec un suivi d’interface par une méthode de front-tracking. On présente des simulations 2D d’écoulements d’eau incluant des bulles d’air, soumises à une variation de pression thermodynamique ou à un chauffage.

International audience; abstract