Annonces et offres d'emploi

Going back to Kolmogorov, there has been the paradigm in the more fundamental turbulence community of one universal state of homogeneous isotropic turbulence. In the last 15 years or so it has become more and more clear that this is not the case and that there can be several different states of turbulence, with transitions between these states. The transitions between the different states normally are of subcritical nature, just as the transition from laminar pipe or channel flow to turbulent pipe of channel flow. There, the origin of the subcritical nature is the nonnormality of the operator, combined with the nonlinearity of the Navier-Stokes equation. The nonnormality is intimately related to the local shear of the flow. All this also holds for turbulent flow, where one locally also has strong shear.

Multiphase flows are common in nature and engineering. Atmospheric flows often involve the dispersion of droplets or solid particulate matter (dust, sand, ice crystals in clouds); marine systems are populated by plankton, sediments or microplastics. Industrial applications of disperse flows include particle separators,filtration systems, atomisers and combustion devices, spray dryers, bubble columns; interfacial and free-surface flows are widespread in chemical and process industry.

Création de la Division Physique Non Linéaire (DPNL) de la Société Française de Physique (SFP)

Cet ouvrage présente les bases de la turbulence aux chercheurs en écologie marine, et les couplages de l’écologie marine avec la turbulence, aux chercheurs en turbulence provenant d’autres disciplines. Il s’adresse aux doctorants, jeunes chercheurs et chercheurs confirmés intéressés par ces deux sujets et leurs interactions.

The Leeds Institute for Fluid Dynamics is delighted to partner with the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge, the UK Fluids Network, and the Journal of Fluid Mechanics to deliver a regular webinar series on fluids-related topics.

This topic aims to better understand and model the resuspension mechanisms ofmicroparticles exposed to accelerated airflows. Previous works led to the development of anexperimental setup and yielded several results concerning the links between flow dynamicsand the resuspension of spherical particles, , but the nature of the initial particle motion (rolling or sliding along the surface,lift-off in the airflow, rebound(s), collisions between particles, etc.) remains difficult todetermine, particularly when initial concentrations are high. Current models lack precisionand would benefit from being enhanced by incorporating the nature of the initial motion andthe associated probability of resuspension. The thesis will therefore focus on (i) continuing andenriching the stochastic modeling of resuspension using previously acquired measurements, and (ii) experimentally measuring thedynamics of particles more precisely during the initial moments of resuspension.

Within the context of human speech productions, waveguide acoustics is well studied for steadygeometries and in absence of flow. Nevertheless, human speech sound production involvesarticulation and respiratory airflow, which are omitted from most studies dealing with the physics ofspeech production. As such, the originality of the proposed PhD is two-fold in addressing firstly theinfluence of time-varying waveguide properties (area, cross-section shapes, elasticity) on acousticwave propagation and secondly in accounting for wave propagation and generation in presence ofairflow. This last aspect implies to address the influence of waveguide dynamics on the generationand interaction of different sound sources – e.g., due to a fluid-structure interaction for voiced sounds or of aero-acoustic nature for fricatives – as well as the influence of waveguide’s wall properties on sound propagation and interaction.

Contact: Gauthier Verhille

The Earth’s hydrosphere, in particular the large-scale circulations of oceans and subglacial lakes, is shaped bytemperature conditions and heat fluxes. For instance, the difference in surface ocean temperatures betweenthe equator and poles helps drive the Atlantic Meridional Overturning Circulation (AMOC), while variable icesheet thicknesses can drive similar large-scale flows in subglacial lakes. Ocean and subglacial lake circulationscan change abruptly when forcing conditions evolve, such as surface air temperatures rising due to climatechange. Here, our aims are to characterize the different dynamical regimes of key components of the Earth’shydrosphere, identify thresholds for regime changes in parameter space, and investigate the nature oftransitions. To make progress, we will investigate idealized models of oceans and subglacial lakes, whichinclude the physical processes key to surface and subglacial environments.

Building on recent advances in mean-field-based linearised modelling for aeroacoustics, and in particularfor modelling sound generation by flow–structure interaction, the 2AT group is developing resolvent-based shape-optimisation tools. The successful candidate will collaborate with Airbus and 2AT researchers to developan adjoint-based shape-optimisation framework for landing-gear aeroacoustics. The numerical methodology will rely on a resolvent formulation of the Boundary Element Method. Optimised geometries will be tested in theanechoïc windtunnels of Institut PPRIME using microphone-array based source localisation.

Building on recent advances in mean-field-based linearised models for turbulent jet dynamics and aeroacoustics, the 2AT group has developed resolvent-based tools for jet-noise modelling, estimation, and control. The successful candidate will collaborate with Airbus and 2AT researchers to extend these tools to fullythree-dimensional mean fields. We aim to develop a high-order finite-difference resolvent solver, incorporatingstabilising filters and a domain-decomposition strategy suitable for complex geometries. Efficient time-integration methods will be employed to compute resolvent modes. The resulting framework will support the development of next-generation models for turbulent jets and jet noise.

Building on recent advances in mean-field-based linearised models for turbulent jet dynamics and aeroacoustics, the 2AT group has developed resolvent-based tools for jet-noise modelling, estimation, and control. The successful candidate will use these tools—working in collaboration with Airbus and 2AT researchers—to develop a predictive model for sound radiation associated with the dominant resolvent modes, explicitly accounting for decoherence effects arising from two-point turbulence statistics. This framework will initially be validated on axisymmetric jets and subsequently applied to fully three-dimensional cases.

Building on recent advances in modal decomposition for the identification of coherent structures in turbulentshear flows, the 2AT group is developing physics-based data-compression strategies for the mining andanalysis of large datasets generated by high-fidelity numerical simulations. The successful candidate will focuson developing and benchmarking modal-decomposition techniques—using on-the-fly approaches—applied todata produced by airframe aeroacoustics simulations.

We will investigate the interaction between weakly inhomogeneous turbu-lence and sedimenting particles which are larger than the smallest flow structures. The objectiveis to determine the influence of particle size and concentration on both the particle motion andthe fluid flow. The study, which will be carried out in collaboration with a partner team in Franceperforming laboratory experiments, can be expected to generate unprecedented data-sets al-lowing for new insight into long-standing problems.

This project is a postdoctoral proposal in the stochastic physics of turbulence aiming to analyze stylized models of multifractal transport and to assess their relevance for turbulent transport.

The work proposed will investigate the interaction of a single fluid vortex and a liquid/gas interface in various configurations through theoretical/numerical modelling and stability analyses.

Dans le cadre du projet « MAchine LEArning for Fluid system efficiency » (MALEAF), soutenu par l’Agence Nationale de la Recherche, l’Ecole Navale recrute un chercheur post-doctorant en mécanique des fluides expérimentale, analyse et assimilation de données d’écoulement pour 2 ans.Mots clés : PIV, POD, assimilation de données, modèle d’ordre réduit, hydrofoils

The wind turbine production in a floating wind farm depends essentially on its position, the wind and the state of the sea. The influence of the state of the sea, in particular, is poorly known, because it has not been an influential factor in the development of installed wind farms. First of all, the influence of the movement of the platform directly affects the production capacity of the wind turbine. But beyond that, it induces significant modifications to the wake, and in the context of commercial farms, where the turbines are not widely spaced, leads to interactions between turbines which are still unknown. As Numerical simulations are very expensive, from numerical simulation and historical data, the environmental conditions can be modeled by stochastic models which are faster to simulate. hus, by combining these stochastic models with the physical model, it is possible to evaluate the uncertainty relating to the key parameters (extractable energy, wake topology).

https://rejoindre.onera.fr/detail-poste?nPostingId=1327&nPostingTargetId=5036&id=P6VFK026203F3VBQB68LOF6Z3&LG=FR⟨uageSelect=FR

Ingénieur de Recherche et Innovation en calcul scientifique multi-physique, simulations hybrides et optimisation appliqués au secteur naval F/H

Le laboratoire J.A. Dieudonné souhaite recruter un.e Maître.sse de conférence pour renforcer son potentiel en recherche en mathématiques appliquées, avec un profil prioritairement orienté vers l’analyse numérique et le calcul scientifique.

Patrick Bot

Pascale Bouruet-Aubertot, Yannis Cuypers, Julien Lenne

Machine Learning for the Control of Collective Dynamics in Particle-Laden Flows

Eletta Negretti

Romain Monchaux (ENSTA Paris), Romain Volk and Mickaël Bourgoin (ENS Lyon)

V. Resseguier (INRAE), W. Antolin (INRAE), F. Dupuy (AgriOdor)

Bruno Issenmann et Christophe Pirat, en collaboration avec Guillaume Ricard (ENS Lyon) et Éric Falcon (Univ. Paris Cité)

E. Negretti, O. Marchand

Eletta Negretti

Partially-magnetized E×B plasmas, where electrons are magnetized but ions are not, are key to technologies like Hall thrusters and ion sources for neutral beam injection for fusion. These plasmas host electrostatic instabilities (e.g., gradient-drift, lower-hybrid, electron cyclotron drift, modified two-stream) that can lead to wave turbulence. This project aims to study wave turbulence-driven transport with a pseudo-spectral solver. The focus is on understanding large-scale structure formation and the impact of parameters like gradients and boundaries. Results will be validated against kinetic simulations and will be used to assess the impact of the turbulent transport into macroscopic quantities as compared to experiments of electric propulsion thrusters.