Umberto D'Ortona

Aix-Marseille University | AMU · Laboratoire de Modélisation, Mécanique et Procédés Propres

The yield stress and shear thinning properties of mucus are identified as critical for ciliary coordination and mucus transport in human airways. We use here numerical simulations to explore the hydrodynamic coupling of cilia and mucus with these two properties using the Herschel--Bulkley model, in a lattice Boltzmann solver for the fluid flow. Thr...

The origin of large and small particle axial bands in long rotating tumblers is a long-standing question. Using DEM simulations, we show that this axial segregation is due to a Rayleigh-Taylor instability which is characterized by the fact that the density of a granular medium increases with mixing and decreases with segregation. For initially mixe...

The yield stress and shear thinning properties of mucus are identified as critical for ciliary coordination and mucus transport in human airways. We use here numerical simulations to explore the hydrodynamic coupling of cilia and mucus with these two properties using the Herschel–Bulkley model, in a lattice Boltzmann solver for the fluid flow. Thre...

The origin of large and small particle axial bands in long rotating tumblers is a long-standing question. Using DEM simulations, we show that this axial segregation is due to a Rayleigh-Taylor instability which is characterized by the fact that the density of a granular medium increases with mixing and decreases with segregation. For initially mixe...

The interaction between two large spherical particles, called intruders, in a dry granular flow down an incline is brought to light and studied experimentally and numerically. Several parameters are varied, namely, the size ratio between the intruders and the small flowing particles, the thickness of the granular flow, the incline slope and roughne...

Cilia are micro-scale hair-like organelles. They can exhibit self-sustained oscillations which play crucial roles in flow transport or locomotion. Recent studies have shown that these oscillations can spontaneously emerge from dynamic instability triggered by internal stresses via a Hopf bifurcation. However, the flow transport induced by an instab...

This paper extends the partially saturated method (PSM), used for curved or complex walls, to the lattice Boltzmann (LB) pseudopotential multicomponent model and adapts the wetting boundary condition to model the contact angle. The pseudopotential model is widely used for various complex flow simulations due to its simplicity. To simulate the wetti...

Myriads of cilia beat on ciliated epithelia, which are ubiquitous in life. When ciliary beats are synchronized, metachronal waves emerge, whose direction of propagation depends on the living system in an unexplained way. We show on a reconstructed human bronchial epithelium in vitro that the direction of propagation is determined by the ability of...

Pressure oscillations applied to human airways can help patients to evacuate bronchial mucus, a highly non-Newtonian gel. To explore the fluid mechanics aspects of these therapies, we perform numerical simulations of pulsated non-Newtonian fluids in two-dimensional channels. The fluid rheology is modeled with the Herschel-Bulkley law, reproducing t...

Friction at the endwalls of partially filled horizontal rotating tumblers induces curvature and axial drift of particle trajectories in the surface flowing layer. Here we describe the results of a detailed discrete element method study of the dry granular flow of monodisperse particles in three-dimensional cylindrical tumblers with endwalls and cyl...

Friction at the endwalls of partially-filled horizontal rotating tumblers induces curvature and axial drift of particle trajectories in the surface flowing layer. Here we describe the results of a detailed discrete element method study of the dry granular flow of monodisperse particles in threedimensional cylindrical tumblers with endwalls and cyli...

Myriads of cilia beat on ciliated epithelia, which are ubiquitous in life. When ciliary beats are synchronized, metachronal waves emerge, whose direction of propagation depends on the living system in an unexplained way. We show on a reconstructed human bronchial epithelium in-vitro that the direction of propagation is determined by the ability of...

The respiratory tract is protected by mucus, a complex fluid transported along the epithelial surface by the coordinated beating of millions of microscopic cilia, hence the name of mucociliary clearance. Its impairment is associated with all severe chronic respiratory diseases. Yet, the relationship between ciliary density and the spatial scale of...

The accuracy of the lattice-Boltzmann (LB) method is related to the relaxation time controlling the flow viscosity. In particular, it is often recommended to avoid large fluid viscosities in order to satisfy the low-Knudsen-number assumption that is essential to recover hydrodynamic behavior at the macroscopic scale, which may in principle limit th...

In the lung, the airway surface is protected by mucus, whose transport and evacuation is ensured through active ciliary beating. The mechanisms governing the long-range directional organization of ciliary beats, required for effective mucus transport, are much debated. Here, we experimentally show on human bronchial epithelium reconstituted in-vitr...

Dry-granular material flowing on rough inclines can experience a self-induced Rayleigh-Taylor (RT) instability followed by the spontaneous emergence of convection cells. For this to happen, particles are different in size and density; the larger particles are denser but still segregate toward the surface. When the flow is initially made of two laye...

Dry granular material flowing on rough inclines can experience a self-induced Rayleigh-Taylor (RT) instability followed by the spontaneous emergence of convection cells. For this to happen, particles are different in size and density, the larger particles are the denser but still segregate toward the surface. When the flow is, as usual, initially m...

The lattice Boltzmann method often involves small numerical time steps due to the acoustic scaling (i.e., scaling between time step and grid size) inherent to the method. In this work, a second-order dual-time-stepping lattice Boltzmann method is proposed in order to avoid any time-step restriction. The implementation of the dual time stepping is b...

In the lung, the airway surface is protected by mucus, whose transport and evacuation is ensured through active ciliary beating. The mechanisms governing the long-range directional organization of ciliary beats, required for effective mucus transport, are much debated. Here, we experimentally show on human bronchial epithelium reconstituted in-vitr...

The respiratory tract is protected by mucus, a complex fluid transported along the epithelial surface by the coordinated beating of millions of microscopic cilia, hence the name of mucociliary clearance. Its impairment is a strong marker of severe chronic respiratory diseases. Yet, the relationship between ciliary density and the spatial scale of m...

The coordinated beating of epithelial cilia in human lungs is a fascinating problem from the hydrodynamics perspective. The phase lag between neighbouring cilia is able to generate collective cilia motions, known as metachronal waves. Different kinds of waves can occur, antiplectic or symplectic, depending on the direction of the wave with respect...

Viscosity independence of lattice-Boltzmann methods is a crucial issue to ensure the physical relevancy of the predicted macroscopic flows over large ranges of physical parameters. The immersed-boundary (IB) method, a powerful tool that allows one to immerse arbitrary-shaped, moving, and deformable bodies in the flow, suffers from a boundary-slip e...

Recent results on the understanding of the beating of epithelial cilia in human lungs to transport bronchial mucus will be presented. This process, known as mucociliary clearance, is at the roots of several chronic respiratory diseases. Using a numerical solver based on the lattice Boltzmann method, we find that the metachronal waves generated by t...

A simulation tool based on lattice Boltzmann and immersed boundary is used to investigate the transport and mixing properties of mucociliary clearance in human lungs. The cilia are beating in a two-components fluid: the periciliary layer (PCL) and the mucus above it. A collective motion of the cilia can emerge, which takes the form of metachronal w...

To better understand the velocity field and flowing layer structure, we have performed a detailed discrete element method study of the flow of monodisperse particles in a partially filled three-dimensional cylindrical rotating tumblers. Similar to what occurs near the poles in spherical and conical tumblers, recirculation cells (secondary flows) de...

The fluid transport and mixing induced by beating cilia, present in the bronchial airways, are studied using a coupled lattice Boltzmann—Immersed Boundary solver. This solver allows the simulation of both single and multi-component fluid flows around moving solid boundaries. The cilia are modeled by a set of Lagrangian points, and Immersed Boundary...

Dans ce travail, la méthode Lattice Boltzmann couplée à la méthode des frontières immergées est utilisée pour étudier l'émergence d'ondes métachronales antipleptiques et symplectiques dans des rangées 3D de cils immergés dans un environnement diphasique, avec un rapport de viscosité de 20. La couche de fluide périciliaire (PCL) est confinée entre l...

This work reports the formation and ^characterization of antipleptic and symplectic metachronal waves in 3D cilia arrays immersed in a two-fluid environment, with a viscosity ratio of 20. A coupled lattice Boltzmann–immersed-boundary solver is used. The periciliary layer is confined between the epithelial surface and the mucus. Its thickness is cho...

The present work reports the formation and the characterization of antipleptic and symplectic metachronal waves in 3D cilia arrays immersed in a two-fluid environment, with a viscosity ratio of 20. A coupled lattice-Boltzmann-Immersed-Boundary solver is used. The periciliary layer is confined between the epithelial surface and the mucus. Its thickn...

Monodisperse and bidisperse granular flows are studied in rotating tumblers using DEM. In spherical tumblers, flowing particles’ trajectories do not follow straight lines but are curved. At the same time particles near the surface drift toward the pole, inducing two global recirculation cells. Combined with radial segregation, drift and curvature c...

In a dry granular flow, the position of a large tracer is numerically studied, first in a half filled rotating tumbler, then in a flow down a rough incline; all particles having the same density. Two (2D) and three (3D) dimensional cases are distinguished, with similar behaviours, but also discrepancies. In the tumbler, the tracer segregated positi...

The present work reports the emergence of metachronal waves in cilia arrays immersed in a two-fluid environment using a coupled lattice Boltzmann-Immersed Boundary method. The periciliary layer (PCL) is confined between the wall and the mucus layer. Its depth is chosen in such a way that the tips of the cilia can penetrate the mucus layer. The cili...

Size bidisperse granular materials in a spherical tumbler segregate into two different patterns of three bands with either small particles at the equator and large particles at the poles or vice versa, depending upon the fill level in the tumbler. Here we use discrete element method (DEM) simulations with supporting qualitative experiments to explo...

Walls in discrete element method simulations of granular flows are sometimes modeled as a closely packed monolayer of fixed particles, resulting in a rough wall rather than a geometrically smooth wall. An implicit assumption is that the resulting rough wall differs from a smooth wall only locally at the particle scale. Here we test this assumption...

In this work, one proposes an immersed boundary-lattice Boltzmann coupled algorithm to solve single-and multi-component fluid flows, in the presence of fixed or moving solid boundaries. The prescribed motion of immersed boundaries is imposed by adding a body force term in the lattice Boltzmann model, which is ob-tained from the macroscopic fluid ve...

Models of monodisperse particle flow in partially filled three-dimensional tumblers often assume that flow along the axis of rotation is negligible. We test this assumption, for spherical and double cone tumblers, using experiments and discrete element method simulations. Cross sections through the particle bed of a spherical tumbler show that, aft...

We have performed DEM simulations and experiments for monodisperse particles in partially-filled spherical tumblers to better understand the flow of bidisperse particles in spherical tumblers, which display segregation patterns that result from differential axial migration of the two species. Particle tracking in DEM simulations for a 30% full tumb...

Two sets of wire mesh tomography sensors have been developed for the study of liquid maldistribution in trickle bed reactors. The technique, based on the one used by Prasser et al. [H.M. Prasser, A. Böttger, J. Zschau, A new electrode-mesh tomograph for gas–liquid flows, Flow Meas. Instrum. 9 (1998) 111–119] in bubble columns, uses two horizontal p...

In this study, we use volume-penalization to mimic the presence of obstacles in a flow or a domain with no-slip boundaries. This allows in principle the use of fast Fourier spectral methods and coherent vortex simulation techniques (based on wavelet decomposition of the flow variables) to compute turbulent wall-bounded flow or flows around solid ob...

Deux systèmes de tomographie à fils ont été utilisés pour étudier la maldistribution du liquide dans un réacteur à lit fixe arrosé en écoulement à co-courant descendant de gaz et de liquide (RCLFA). La technique, qui se base sur celle utilisée par Prasser et coll. (1998) dans les colonnes à bulles, utilise deux faisceaux de fils horizontaux placés...

A two-dimensional two-colour, nonlinear, Galilean-invariant, Boltzmann cellular automaton is developed and used to study two-fluid hydrodynamics and to model fluid interfaces. The interfacial tension and interface width are flexibly controlled by the parameters defining collision rules for the colored particles. Results of studies of both the stati...

The flow of dry granular material in a half-filled rotating drum is studied. The thickness of the flowing zone is measured for several rotation speeds, drum sizes and beads sizes (size ratio between drum and beads ranging from 47 to 7400). Varying the rotation speed, a scaling law linking mean velocity vs. thickness of the flow, v approximately h(m...

Heat transfer performances for non-boiling and boiling flow of a micro-vaporizer have been measured by standard methods (temperatures, flow rates, effective power input). The study was carried out for laminar flow (Re<25) in silicon micro-channels () filled with ordered obstacles to increase the specific area. The results obtained show a strong dep...

The heat transfer performance of a micro-vaporizer has been measured by conventional methods (using temperatures, flow rates, effective power input). The study was carried out for laminar flow in channels (5 mm×3 cm×200 μm) micro-structured with square obstacles to increase the specific area. The results show that high heat transfer coefficients (1...

A polydisperse sedimentation model and a polydisperse packing model are joined together to describe the sedimentation of a suspension which particle size distribution spreads over several decades. The model is applied to the centrifugation of mortar.

We study experimentally the maximum thickness of the flowing zone in a rotating drum of diameter D half filled with glass beads of diameter d. Several drum diameters and beads sizes were studied, bringing a special attention to geometrically similar systems, i.e. of constant ratio D/d. The rotation speed ranges from 2 to 20 rpm, the minimum is chos...

The mini heat-exchangers presented here are cubic, cross-flow type exchangers with several specific features, concerning the internal design, the material, and the method of fabrication. The overall dimensions are of the order of several centimetres, while the internal channels have characteristic dimension in the millimetre range. The different “l...

The behavior of monomolecular layers of fluid spreading on a solid substrate is examined using molecular dynamics simulations of polymerlike liquids. We consider drops of chain molecules of lengths 8 and 16, composed of Lennard-Jones atoms bound by confining potentials, spreading on an atomic solid substrate. Different strengths of the solid-fluid...

Using a two-dimensional, two-color lattice Boltzmann automaton, the dynamics of the contact angle characterizing a fluid/fluid interface in contact with a moving substrate is simulated numerically. It is found that the velocity dependence of the contact angle is consistent with the molecular kinetic theory.

We have designed and tested a two-color nonlinear Boltzmann cellular atuomaton to study hydrodynamic phenomena related to surface tension and wetting in two dimensions. Our rules for collisions of colored particles allow for both miscibility and flexible control of the interfacial tension and the interface thickness. The contact angle of two fluids...

Using molecular dynamics simulations, we study the dynamics of the spreading of liquid drops of chain molecules on a solid substrate. In contrast to previous work with monatomic or diatomic fluids, the radius of the spreading layers increases with time with a power law compatible with the sqrt[t] behavior observed experimentally in polymeric fluids...

The results of numerical calculations of the velocity profiles and the viscosities of Boolean and Boltzmann cellular automata for circular Couette flows in two dimensions are presented. The necessary forcing rules to induce such flows are constructed. It is shown that the Boltzmann cellular automata offer a more natural way of simulating flows arou...

Results of cellular automata based studies of mixing in a square cavity are presented. Two periodic models are considered: one in which two walls move in opposite directions one at a time and the other in which they act simultaneously but alternate the directions of motion. Both flows are found to be chaotic and the Poincare sections and Lyapunov e...

The peak pattern of a magnetic fluid, in both a vertical dc and an additional vertical ac magnetic field, behaves as an oscillator. Using the ac-dc field ratio as a control parameter, we study the dynamics of this oscillator. For low values, the peaks oscillate at the ac field frequency, whereas for a large enough value the oscillation is subharmon...

Nous présentons une confrontation entre différentes méthodes numériques pour résoudre les équation de Navier-Stokes : Volumes Finis, Différences Finies, Fourier, Tchebyshev, Gaz de Boltzmann, Ondelettes, ... pour l'étude de la collision entre un dipôle et une paroi non glissante. La précision obtenue en fonction de la résolution, l'ordre des méthod...

Nous présentons une étude expérimentale et numérique de l'écoulement sur plan incliné de milieux granulaires monodisperse et bidisperse ségrégé. Après présentation des profils de vitesse théoriques attendus, et ceux observés expérimentalement et numériquement, que l'augmentation de la vitesse d'écoulement par la présence de grandes particules à la...