Julien Favier

Aix-Marseille Université | AMU · Faculté des Sciences

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 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 Ozaki procedure is a surgical technique which avoids to implant foreign aortic valve prostheses in human heart, using the patient’s own pericardium. Although this approach has well-identified benefits, it is still a topic of debate in the cardiac surgical community, which prevents its larger use to treat valve pathologies. This is linked to the...

OBJECTIVES Three-dimensional (3D) modelling of aortic leaflets remains difficult due to insufficient resolution of medical imaging. We aimed to model the coaptation and load-bearing surfaces of the aortic leaflets and adapt this workflow to aid in the design of aortic valve neocuspidizations. METHODS Geometric morphometrics, using landmarks and se...

Fluid–structure interaction (FSI) occurs in a wide range of contexts, from aeronautics to biological systems. To numerically address this challenging type of problem, various methods have been proposed, particularly using implicit coupling when the fluid and the solid have the same density, i.e., the density ratio is equal to 1. Aiming for a comput...

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...

The numerical instability of the lattice Boltzmann method (LBM) at high Mach or high Reynolds number flow is well identified, and it remains a major barrier to its application in more complex configurations such as moving geometries. This work combines the compressible lattice Boltzmann model with rotating overset grids (the so-called Chimera metho...

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...

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...

An immersed boundary method is coupled to a turbulent wall model and Large Eddy Simulation, within the Lattice-Boltzmann framework. The method is able to handle arbitrarily moving objects immersed in a high Reynolds number flow and to accurately capture the shear layer and near wall effects. We perform a thorough numerical study which validates the...

Simulating rotating geometries in fluid flows for industrial applications remains a challenging task for general fluid solvers and in particular for the lattice Boltzmann method (LBM) due to inherent stability and accuracy problems. This work proposes an original method based on the widely used overset grids (or Chimera grids) while being integrate...

We propose a new direct coupling scheme based on the overset technique to tackle moving boundary problems within the lattice Boltzmann framework. The scheme is based on the interpolation of distribution functions rather than moments, that is, macroscopic variables, and includes an additional hypothesis ensuring mass and momentum conservation at the...

The boundary slip error resulting from the interpolation/spreading non-reciprocity of the direct-forcing immersed-boundary method is analyzed based on a simple and generic theoretical framework. In explicit implementations, the slip error scales with the Courant number, as predicted by the analysis and confirmed by lattice-Boltzmann simulation resu...

Background Management of patients with complex congenital heart defects (CHD) requires 3D imagination skills for the spatial evaluation of cardiac structures. Current 3D imaging [echocardiography, MRI, computed tomography (CT)], projected on a 2D screen, limits the appreciation of the relief and the interaction of anatomical structures. Purpose Th...

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...

Airway mucus is a complex material from a rhe-ological point of view exhibiting a yield stress, shear-thinning, viscoplastic and thixotropic properties. Collecting real mucus being quite challenging and inducing a huge variability of the samples, mucus simulants are usually preferred to investigate in details its rheology and derive behavioral law,...

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 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...

Introduction: La kinésithérapie respiratoire (KR) comprenant le drainage bronchique (DB) est une mesure essentielle de la prise en charge de la mucoviscidose (CF), dans le but de limiter les surinfections bronchiques et la dégradation fonctionnelle respiratoire. Divers protocoles et techniques ont été proposés pour optimiser la qualité du DB. Dans...

The three-dimensional flow around a sphere is one of the most classical subjects of investigation for fundamental analysis of external aerodynamics. In fact this flow configuration, which is described by a very simple geometrical shape, exhibits the potential for complex multi-physics analysis. Some aspects that can be investigated include turbulen...

The development of an improved IBM method is proposed in the present article. This method roots in efficient proposals developed for the simulation of incompressible flows, and it is expanded for compressible configurations. The main feature of this model is the integration of a pressure-based correction of the IBM forcing which is analytically der...

This chapter presents several partitioned algorithms to couple lattice Boltzmann method (LBM) and finite element method (FEM) for numerical simulation of transient fluid-structure interaction (FSI) problems with large interface motion. Partitioned coupling strategies allow one to solve separately the fluid and solid subdomains using adapted or opti...

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...

The development of an improved IBM method is proposed in the present article. This method roots in efficient proposals developed for the simulation of incompressible flows and it is extended for compressible configurations. The main feature of this model is the integration of a pressure-based correction of the IBM forcing which is analytically deri...

In this work, a complete rheological characterization of bronchial mucus simulants based on the composition proposed by Zahm et al. [1] is presented. Dynamic Small Amplitude Oscillatory Shear (SAOS) experiments, Steady State (SS) flow measurements and three Intervals Thixotropy Tests (3ITT), are carried out to investigate the global rheological com...

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...

The present work proposes a modified Pressure-Implicit Split-Operator (PISO) solver integrating the recent Immersed Boundary Method (IBM) proposed by [1] in order to perform reliable simulations of incompressible flows around bluff bodies using the open source toolbox OpenFOAM version 2.2 ([2]). The (IBM) allows for a precise representation of fixe...

In this paper, dynamic viscosity, surface tension, density, heat capacity and thermal conductivity, of a bronchial mucus simulant proposed by Zahm et al. [1991] were experiementally determined. This simulant is mainly composed of a galactomannan gum and a scleroglucan. It was shown that thermophysical properties of synthetic mucus are dependant of...

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...

A novel implicit immersed boundary method of high accuracy and efficiency is presented for the simulation of incompressible viscous flow over complex stationary or moving solid boundaries. A boundary force is often introduced in many immersed boundary methods to mimic the presence of solid boundary, such that the overall simulation can be performed...

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...

A novel immersed boundary method is introduced for simulating the fluid-structure interaction problem. Unlike the body-conforming mesh method which imposes the no-slip boundary conditions directly on the immersed interface, the immersed boundary method adopts a boundary force for the presence of the immersed solid. Therefore, the fluid is simply si...

The paper presents a numerical framework for the coupling of finite element and lattice Boltzmann methods for transient problems involving fluid-structure interaction. The solid structure is discretized with the finite element method and integrated in time with the explicit Newmark scheme. The lattice Boltzmann method is used for the simulation of...

based on the Generalized Lattice Boltzmann method, which models the flow in the Representative Elementary Volume scale including the porous effects (porosity and the Brinkman-Forchheimer extended Darcy force model), coupled to the Immersed Boundary method to handle complex geometries and moving bodies. The coupling between both methods will be pres...

The fluid-structure interaction mechanisms of a coating composed of flexible flaps immersed in a periodically oscillating channel flow is here studied by means of numerical simulation, employing the Euler-Bernoulli equations to account for the flexibility of the structures. A set of passively actuated flaps have previously been demonstrated to deli...

In this paper, the Immersed Boundary Method (IBM) proposed by Pinelli is implemented for finite volume approximations of incompressible Navier-Stokes equations solutions in the open source toolbox OpenFOAM version 2.2. Solid obstacles are described using a discrete forcing approach for boundary conditions. Unlike traditional approaches encompassing...

Previous studies of flexible flaps attached to the aft part of a cylinder have demonstrated a favourable effect on the drag and lift force fluctuation. This observation is thought to be linked to the excitation of travelling waves along the flaps and as a consequence of that, periodic shedding of the von Kármán vortices is altered in phase. A more...

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...

Mucus is mainly composed of water (90-95%) and mucins (2-5%), these mucins being high molecular weight macromolecules forming a 3D cross-linked matrix. It makes it a complex non-Newtonian fluid, displaying viscoplasticity, viscoelasticity, shear-thinning and thixotropy. These properties were qualitatively and separately tested by different authors....

In this work, we propose a numerical framework to simulate fluid flows in interaction with moving porous media of complex geometry. It is based on the Lattice Boltzmann method including porous effects via a Brinkman–Forchheimer–Darcy force model coupled to the Immersed Boundary method to handle complex geometries and moving structures. The coupling...