Laboratoire de Mécanique des Fluides et d'Acoustique - UMR 5509

Informations pratiques

Gostiaux Louis — 2100-10-17T10:08:00Z

Les séminaires du LMFA ont lieu le vendredi à 11h, et s'adressent à l'ensemble du laboratoire.
contact : louis.gostiaux@ec-lyon.fr, wouter.bos@ec-lyon.fr, benjamin.miquel@ec-lyon.fr
Pour accéder au laboratoire voir ici

Documents utiles :

Séminaires T&I

2027-03-03T16:25:00Z

Les séminaires de l'équipe se tiennent le jeudi de 12h00 à 12h45. Une présentation de 30 min, laissant place aux questions et échanges. Un séminaire sur trois est donné sur le campus de la DOUA.

Pour s'abonner au calendrier des séminaires, vous pouvez utiliser ce lien Ical

Vous pouvez retrouver les anciens séminaires ici

Séminaire informel

Romain Vallon

Vendredi 18 juillet 2025 à 13h, ECL, bât. I11, salle de conférence du bas

Accélération GPU pour le calcul des fonctions de structures
Les volumes de données générés à l'aide de DNS sont conséquents. Le traitement de ces données peut être long (quelques heures), voire très long (...)

Séminaires passés 2024 :

Séminaire informel T&I

Mathieu Creyssels

Vendredi 3 Mai 2024 à 14h, ECL, bât. I11, salle de conférence du bas

Mélange turbulent et entraînement dans les jets, panaches et courants de gravité
Le mélange turbulent est le processus physique qui contrôle la dispersion des espèces chimiques dans les écoulements (...)

Séminaire informel T&I

Joran Rolland

Lundi 6 mai, 14h, salle B11, bât. H10, ECL

Using learnt stochastic model to study the regime change of a bistable wake
When two parallel bars of thickness H, in a flow at Reynolds number R $= HU/\nu\simeq 10000$, are brought close enough (...)

Séminaire informel T&I

Anne Sergent

Mardi 7 mai, 14h, salle B11, bât. H10, ECL

Panaches et circulation à grande échelle en convection turbulente asymétrique : modélisation HPC et apprentissage automatique
Les écoulements de convection naturelle sont présents aussi bien en (...)

Séminaire informel T&I

Jérôme Boudet

Lundi 13 mai, 10h, salle B11, bât. H10, ECL

Écoulements tourbillonnaires à haut Re : méthodes et analyses en simulation des grandes échelles.
L'aérodynamique repose des écoulements tourbillonnaires, généralement à haut nombre de Reynolds, et donc (...)

Séminaire informel T&I

Annick Pouquet

Mercredi 29 Mai à 11h, Salle B11, bât. H10, ECL

Some characteristics of intermittency for energy dissipation : ideas and results
Our understanding of turbulence has progressed significantly through combining experiments, observations, (...)

PhD proposal : Inverse modelling of atmospheric dispersion and soil deposition of PFAS for source identification

Scolan Hélène — 2026-06-05T13:47:56Z

Inverse modelling of atmospheric dispersion and soil deposition of PFAS for source identification

Supervisor : Prof. Pietro Salizzoni (LMFA, ECL) and Prof Lionel Soulhac (LMFA, INSA Lyon).

Scientific context :
Per- and polyfluoroalkyl substances (PFAS) are synthetic chemical compounds containing chains of carbon atoms bonded to fluorine atoms. The carbon-fluorine bonds are very stable, making PFAS extremely persistent in the environment and resistant to water and high temperatures. Due to these characteristics, PFAS are used in a wide range of industrial and domestic products : non-stick and stain-resistant coatings, cosmetics, fire-fighting foam, waterproof clothing, etc. Furthermore, PFAS have an affinity for proteins and lipids, so they tend to accumulate in living organisms or in the food chain. Due to their persistence and physicochemical properties, PFAS transfer into various environmental compartments (air, soil, water, eggs, crops) and can migrate several kilometres away from the source of emission, making it difficult to reconstruct emission scenarios consistent with environmental observations.
In this context, inverse modelling is an effective approach to identify emission sources and intensities, based on measurements of PFAS concentrations in the environment. In particular, this approach has been used to identify the sources of PFAS emissions detected in various environmental compartments in the Lyon metropolitan area, which is known for the presence of factories that produce and use PFAS. The ubiquity of PFAS requires dispersion models to account for several mechanisms, including atmospheric transport in the gaseous and particulate phases, resuspension, redeposition and infiltration into deep soil layers, and transfer from soil into the food chain via eggs. The aim of the project will be to analyse these phenomena in order to develop direct models of atmospheric dispersion of PFAS, transport in soil, and transfer into the food chain. These direct models, combined with inverse modelling approaches, will enable the construction of emission scenarios that explain the levels of PFAS contamination detected in soil, air, or egg samples collected from the environment.

Expected work :

The thesis involves modelling the atmospheric dispersion of PFAS, their deposition on the ground, and their transfer into chickens' eggs. The atmospheric dispersion of PFAS will be carried out using the urban dispersion model SIRANE, developed at the Laboratoire de Mécanique des Fluides et d'Acoustique of l'Ecole Centrale de Lyon. From weather data, emission scenarios and the physical characteristics of the pollutants, SIRANE provides maps of pollutant concentrations in the air and soil deposition fluxes. Parametric transport models will be developed to reconstruct the transport in soil and the transfer of PFAS into the food chain. Using an inverse modelling algorithm, the PFAS concentrations predicted by the models will be compared with measured PFAS levels in the air, soil and chicken eggs, in order to identify the flow rates and locations of sources that minimise the discrepancy between the observations and the simulations.
Field or wind-tunnel measurements of PFAS concentrations could be carried out to explore new contamination scenarios and to extend the application of the inverse modelling methodology developed during the PhD to different contexts.

More details and for application, see :

TBA

Miquel Benjamin — 2026-06-01T10:57:08Z

- Séminaires

TBA

Bos Wouter — 2026-05-23T13:38:26Z

Flow regimes and bifurcations in spherical Couette flows

Miquel Benjamin — 2026-05-20T15:54:17Z

Spherical Couette flow, generated by the differential rotation between concentric spheres, exhibits a wide range of complex flow instabilities and transition mechanisms relevant to geophysical and engineering applications. In this talk, numerical simulations of incompressible spherical Couette flow are presented for a narrow-gap configuration with only the inner sphere rotating. The governing Navier–Stokes equations in spherical coordinates are solved using a pseudo-spectral method. Particular emphasis is placed on the sensitivity of the flow to initial conditions and the resulting multiplicity of solution branches. Using different initial conditions, multiple branches of the bifurcation diagram are identified, each dominated by distinct instability mechanisms. Three primary branches
are observed : an axisymmetric branch, a travelling-wave instability branch, and an equatorial instability branch. The axisymmetric branch becomes unsteady at sufficiently large Reynolds numbers. The travelling-wave branch is characterized by spiral instabilities concentrated near the polar regions and exhibits an interesting reversal in the propagation direction of the spiral waves as the Reynolds number increases. At higher Reynolds numbers, this branch further develops multi-mode equatorial instabilities. The equatorial instability branch is associated with the formation of twin jet-like structures on either side of the equator, which themselves become unstable as the Reynolds number is increased. The flow topology and dynamical behaviour of these branches are further analysed in phase space. The travelling-wave branch, in particular, demonstrates
signatures of chaotic dynamics at large Reynolds numbers. The results provide insights into the nonlinear dynamics, multiplicity, and transition characteristics of spherical Couette flow in narrow-gap geometries.

Giovanni Coco

Scolan Hélène — 2026-05-07T10:19:48Z

Propagation of Shock Waves Generated by un Unducted Single Fan : Acoustic Signature on the Fuselage

Jury :
M. Benjamin Cotté, Maître de conférences HDR, ENSTA Paris, Rapporteur
M. Francesco Avallone, Professeur, Politecnico di Torino, Rapporteur
M. Régis Marchiano, Professeur, Sorbonne Université, Examinateur
M. Christophe Bailly, Professeur, École Centrale de Lyon, Directeur de thèse
M. Didier Dragna, Maître de conférences HDR, École Centrale de Lyon, Co-encadrant
Mme Hélène de Laborderie, Ingénieure experte, Safran Aircraft Engines, Co-encadrante

Summary :

The transition toward sustainable aviation has intensified interest in unducted aero-engines as a means of achieving substantial reductions in fuel consumption. The absence of a conventional engine nacelle in such configurations, however, removes a primary location for acoustic treatment and allows non-linear acoustic fluctuations generated at blade tips to propagate directly toward the aircraft fuselage. Existing aeroacoustic prediction methods often rely on linear acoustic analogies that neglect non-linear propagation effects or require computationally expensive body-fitted meshes to account for installation phenomena.
The objective of this dissertation is to develop and validate a high-fidelity numerical framework for predicting the acoustic signature induced by an unducted single fan engine on the fuselage, with particular emphasis on non-linear propagation and installation effects. The work addresses key methodological challenges related to robust CFD/CAA coupling and the efficient representation of rigid boundaries within Cartesian computational domains.
The proposed framework is based on a three-dimensional non-linear Euler solver employing high-order, low-dispersion numerical schemes combined with a dedicated shock-capturing strategy. A major contribution of this thesis is the development of a volumetric source method that enables the injection of prescribed acoustic fields from analytical solutions or independent flow simulations without generating spurious reflections. In addition, a novel reflection approach is introduced to model the fuselage as a perfectly rigid obstacle through forcing terms in the momentum equations, enabling accurate boundary treatment on uniform Cartesian grids.
Application of the developed tools provides new physical insight into the mechanisms governing fuselage noise. The results indicate that non-linear propagation effects lead to a limited reduction in sound pressure levels for upstream-propagating waves, whereas refraction by the fuselage boundary layer represents the dominant factor shaping the acoustic signature. Parametric analyses further show that shielding effectiveness increases monotonically with boundary layer thickness and that laminar velocity profiles yield substantially higher attenuation than turbulent profiles.
Overall, the findings suggest that conventional linear approaches may overestimate forward-fuselage noise levels and demonstrate the relevance of boundary layer characterization in installed noise prediction. The numerical framework established in this work offers an efficient and reliable tool for the aeroacoustic analysis and preliminary design of future unducted propulsion systems.

Unexpected Crossover from Weak to Strong Magnetohydrodynamic Turbulence

Miquel Benjamin — 2026-04-20T14:27:04Z

The quest for a consistent theory of magnetohydrodynamic (MHD) turbulence has remained one of the most enduring challenges in physics. In this talk, I will present a universal crossover between weak and strong turbulence regimes. We demonstrate that spectral scaling is fundamentally governed by a competition between the external and local magnetic fields. We show that large mean magnetic field yields Iroshnikov–Kraichnan -3/2 scaling due to weak modulation of Alfvén waves, but moderate and weak magnetic fields produce Kolmogorov's -5/3 scaling driven by strong modulation from the local magnetic field. I connect the above result to the long-sought physical explanation for the evolution of the solar wind spectral index and corona heating in the quiet and active zones.

Turbulence in vegetated environments : numerical modelling and field measurement

Miquel Benjamin — 2026-04-13T06:35:38Z

Aquatic vegetation plays a crucial role in flow hydrodynamics, natural habitats, and morphodynamic evolution, all of which are strongly influenced by the turbulence generated through plant–flow interactions. Understanding the processes controlling turbulence in such environments, and developing predictive models, is therefore of major importance. In this talk, I will focus on rigid vegetation typical of mangrove environments. After reviewing the existing semi-empirical laboratory-based formulations to predict turbulence intensity and bed shear stress in vegetated flows, I will present both numerical and field-measurement results.

First, 3D Large Eddy Simulations (LES) are used to investigate the flow structure and the mechanisms governing the production and evolution of vegetation-induced turbulence, for different Reynolds numbers and a wide range of vegetation densities. Based on these high-resolution simulations, a reduced vegetation-averaged model is developed, together with a new turbulence closure accounting explicitly for vegetation-generated turbulence.

In a second part, I will present results from a field campaign conducted in a mangrove coastal zone in New-Zealand, where turbulence measurements were collected. Acoustic instruments provided high-resolution velocity measurements in a heterogeneous field environment over six tidal cycles. Although the measurements are generally consistent with laboratory-derived formulations, they also highlight the need to better account for and parameterize vegetation heterogeneity in natural environments.

Les travaux de C. Bogey sur les ondes guidées acoustiques mis en avant dans les Highlights 2026 du Journal of Fluid Mechanics

Scolan Hélène — 2026-04-03T14:18:53Z

Les travaux récents de Christophe Bogey (LMFA, CNRS) publiés dans le Journal of Fluid Mechanics ont été sélectionnés par le comité de rédaction du Journal of Fluid Mechanics pour figurer dans sa rubrique « The Editors' Insights 2026 », qui met en avant les articles récents ayant le plus grand impact.

Le rôle clé des modes acoustiques neutres, ou ondes de jet guidé (GJW), dans le bruit des jets y est mis en évidence. Christophe et ses coauteurs travaillent sur ce sujet depuis de nombreuses années, étudiant les mécanismes de génération du bruit dans les jets subsoniques et supersoniques. Félicitations !

Bogey C. Guided-jet waves generated by an acoustic source in a jet at a Mach number of 0.95. Journal of Fluid Mechanics. 2025 ;1024:R1. doi:10.1017/jfm.2025.10910.
Highlight 2026 par Dan Henningson