Les bulles de Taylor sont des poches de gaz allongées occupant la quasi totalité d’une conduite. Elles peuvent être utilisées à dessein ou subites dans de nombreux systèmes industriels. On les observe typiquement dans les écoulements à poches, dont l’étude passe souvent par l’analyse spécifique des bulles de Taylor. Elles ont été largement étudiées aux échelles millimétriques et décimétriques....
The study of two-phase boiling flows is of considerable interest due to its crucial role in optimizing thermal performance across various industrial applications. However, the accurate numerical simulation of such flows remains challenging. In this work, we present a two-phase compressible solver based on the finite volume method, which maintains good accuracy in the low Mach regime. A...
The physical parameter quantifying the wetting behaviour of a droplet on solid surfaces is the contact angle. Several types of contact angles can be defined, mainly the apparent (or macroscopic) contact angle at the scale of the droplet, and the local (or microscopic) contact angle locally estimated at a given point of the contact line between the surface, the droplet, and the air surrounding...
Air entrainment is a process in which gas is incorporated into a bath of liquid. It can be observed at various scales, from breaking waves to the pouring of a glass of water. In both situations, the liquid meets the bath at an angle. In this talk, we will present a study of the mechanism of air entrainment by an oblique capillary jet impacting a bath of water. We will begin by describing the...
The flow of yield stress fluids in porous media is interestingly complex due to the interplay between the medium's heterogeneity and non-linear rheology. For instance, a nonlinear Darcy law emerges as the number of flow paths increases with the applied pressure difference.
In this talk, we will discuss how the boundary conditions influence the flow field. Unlike the Newtonian case, the type...
The transport of deformable particulates through porous media underlies a broad range of processes in biomedicine, energy, and sustainability. Despite its ubiquity and importance, it is still not possible to predict — for a suspension of particulates of a given size, mechanical properties, and injection conditions in a porous medium of a given geometry — what the spatial distribution of...
Measurements are carried out in a turbulent flow behind a grid of dimensions: 150 mm X 300 mm with a squared mesh size of M=40mm. A Dantec 55P11 hot-wire is used with a time resolution frequency much smaller than than the Kolmogorov turnover time scale (5%).
Different mean flow speeds are tested from 13 m/s to 20 m/s corresponding to Taylor Reynolds number values between 190 and 360. The...
Over the past decade, fluidic pinball has emerged as a valuable benchmark for studying flow control strategies (Deng(2020)). The cylinder rotation rates serve as the control inputs and the velocity sensors in the wake provide the outputs. Despite its geometric simplicity, the wake behind the fluidic pinball exhibits complex interactions of multiple frequencies and nonlinear dynamics, making it...
The growth of a turbulent mixing layer driven by the Rayleigh-Taylor instability (RTI) is the result of non-linear interactions between structures of different sizes which merge and compete under the effect of buoyancy forces. In the asymptotic self-similar regime, the mixing layer width evolves as the square of time.
In the Boussinesq approximation, it was shown, considering the simplified...
We have considered several geometries and numerical configurations to model and simulate the Von Karman Sodium (VKS) experiment. The most striking result is that the addition of an immobile sodium layer around the cylinder containing the sodium flow enables magnetic field reversals. In the Von Karman Sodium experiment, a statistically stationary magnetic field is first created by the rotation...
Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) are critical techniques for flow visualization in experimental fluid mechanics. However, the implementation of these methods often requires expensive equipment and generates vast quantities of data.
Recently, a new type of camera, known as an “event-based camera” or “neuromorphic camera,” has become available. Unlike...
Li-ion battery safety is linked to fire and explosion hazards, due to flammable gases produced by the thermal runaway reactions that can accumulate in a confined environment.
To represent large-scale problems, typically a deflagration inside a Battery Energy Storage System container and its potential transition to detonation, the strategy relies on a numerical model relying on the knowledge...
We investigate how surface waves enhance mixing across the interface of two miscible fluids with a small density contrast. Imposing a vertical, time-periodic acceleration, we excite Faraday waves both experimentally and numerically. In systems with a shallow density gradient, these standing waves advect the interface and can trigger secondary instabilities.
When driven beyond the linear...
The microswimmer Chlamydomonas reinhardtii, a quasi-spheric 10 $\mu$m long microalga, is of particular interest for its ability to swim towards or away from light sources, known as phototaxis. When the C. reinhardtii concentration becomes high enough, bio-convective structures can appear and affect the surrounding fluid [1,2].
This study shows how the phototactic behavior of microalgae...
Adding swimming bacteria to a liquid causes its effective shear viscosity to decrease, eventually reaching a regime of zero viscosity. We examined whether this property leads to viscous finger-like displacement fronts like those observed when a less viscous fluid displaces a more viscous liquid. Our study revealed that this system exhibits more complex dynamic characteristics than the...
Interfaces subjected to strong time-periodic horizontal accelerations exhibit striking pat-
terns known as frozen waves. In this study, we experimentally and numerically investigate
the formation of such structures in immiscible fluids under high-frequency forcing. In the
inertial regime–characterized by large Reynolds and Weber numbers, where viscous and
surface tension effects become...
Falling liquid films are utilized in many technological systems to intensify mass and heat transfers. These systems usually involve thin liquid films flowing over complex surfaces with topographical features such as corrugations and perforations. The present study focuses on a falling liquid film flowing over a single circular perforation and the possibility of liquid surface wave...
Le mouvement de flotteurs dans un champ de vagues est un problème fondamental d’interaction fluide-structure aux nombreuses applications en ingénierie navale ou pour le transport de polluants. En plus d’une réponse harmonique (réponse de premier ordre), de tels flotteurs exhibent des mouvements de second ordre, en translation (de type dérive de Stokes) mais aussi en rotation. Nous avons étudié...
Les écoulements à faible nombre de Reynolds avec surface libre représentent un défi majeur en simulation numérique, en raison de l’évolution conjointe de la solution et de l’interface fluide. La Particle Finite Element Method (PFEM) est bien adaptée à ce type de problèmes, car sa formulation lagrangienne permet de suivre naturellement le déplacement de l’interface. Toutefois, son coût de...
In the mining industry, piles of extracted materials present a high risk of avalanches, which can cause damage. To avoid these risks, an effective and inexpensive technique is to add a small quantity of flexible fibers that entangle and increase the stability of the granular piles. This fiber-reinforcement technique used in different contexts such as stabilization of sand dunes or coast-line...
Although many tsunamis are generated by underwater earthquakes, a significant fraction of them can also be generated by the flow or collapse of a great volume of material from the air into a body of water. We have performed experiments using a rectangular granular column, comprised of monodisperse spherical beads made up of low density materials, released by a sluice gate to collapse in a...
When solid grains are mixed with a small amount of liquid, they can form a cohesive aggregate, held together by capillary bridges. Upon impacting a solid surface, such a granular aggregate fragments into multiple pieces. The number and size of these fragments depend on the initial kinetic energy of the aggregate as well as the properties of the grains and the interstitial liquid.
We conduct...
Granular materials are collections of grains, larger than 100 μm, that interact through collisions or solid friction. They encompass a wide variety of materials and are present in many industrial sectors and natural phenomena (mining, landslides, etc.). In all of them, mechanical processes such as segregation, percolation, and diffusion take place when subjected to an external shear force. Of...
This study investigates unsteady flow behavior and transition dynamics in a dual-bell nozzle (DBN) at a nozzle pressure ratio (NPR) of 10 using high-fidelity simulations with the k-omega SST Detached Eddy Simulation (DES) model in OpenFOAM. The baseline (no-injection) case is benchmarked against the cold-flow experiments of Léger et al. (2020). The mesh is refined near walls to resolve key...
Les motifs grande échelle d'alternance laminaire-turbulent en canal plan
sont typiques du régime transitionnel mais restent mal compris. Nous montrons dans cette étude que ces motifs ont comme origine dynamique une modulation de l'écoulement turbulent. Cette modulation peut être prédite numériquement comme une instabilité linéaire lorsque les fluctuations turbulentes ainsi que cohérentes sont...
Despite progress in tsunami modeling, the role of earthquake dynamics in tsunami generation remains underexplored, as traditional models typically assume instantaneous seabed displacement. This study investigates the impact of dynamic rupture processes on tsunamigenesis, a multiscale problem involving high-frequency seismic waves and slower tsunami waves. We introduce a high-order spectral...
Paragliding is a relatively young adventure sport, introduced in the early 1980s, that involves flying lightweight, free-flying, foot-launched glider aircraft without a rigid primary structure. This design inherently leads to instability, particularly during unsteady phases of flight.
This study investigates the stability and dynamics of paragliders during spiral descent, a manoeuvre...
We highlight recent developments of a "Fourier continuation" method for the numerical analysis of parabolic/hyperbolic partial differential equations (PDEs) with complex boundary conditions. The framework relies on a discrete extension approach for the high-order trigonometric interpolation of non-periodic functions (mitigating the notorious Gibb’s “ringing effect"), enabling construction of...
This theoretical study examines the fluid-structure interaction between two coaxial cylinders separated by a Newtonian fluid in a turbulent axial flow. The inner cylinder is modeled as a rigid body mounted on a flexible blade, represented by a Rayleigh beam. We show that vibration modes, frequencies, instability thresholds, and mean-square displacement depend on distinct sets of dimensionless...
Dynamo instability, i.e the amplification of a residual magnetic field by a fluid flow, is generally assumed to be the mechanism behind the emergence of large scale magnetic fields in the universe. In 2006, the von Kármán Sodium (VKS) experiment was able for the first time to produce a dynamo through a highly turbulent flow of liquid sodium driven by two counter-rotating impellers in a...
Turbulent convection is ubiquitous in both industrial and natural fluid flows. A canonical model is the Rayleigh-Bénard convection (RBC): a fluid layer heated from below and cooled from above. With regards to the geometrical configuration, one or several convection cells can appear, which is called Large-Scale Circulation (LSC). The LSC generates a horizontal wind along the horizontal plates...
