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We consider a smooth forward facing step defined by the Gauss error function of height 4-30\% and four times the width of the local boundary layer thickness $\delta_{99}$. The boundary layer flow over a smooth forward-facing stepped plate is studied with particular emphasis on stabilisation and destabilisation of the Tollmien-Schlichting (TS) waves and subsequently on transition. The interaction between TS waves at a range of frequencies and a base flow over a single/two forward facing smooth steps is conducted by linear analysis. The results indicate that for a high frequency TS wave, the amplitude of the TS wave is attenuated in the unstable regime of the neutral stability curve corresponding to a flat plate boundary layer. Furthermore, it is observed that two smooth forward facing steps lead to a more acute reduction of the amplitude of the TS wave. When the height of a step is increased to more than 20\% of the local boundary layer thickness for a fixed width parameter, the TS wave is amplified and thereby a destabilisation effect is introduced. Therefore, stabilisation or destabilisation effect of a smooth step is typically dependent on its shape parameters. To validate the results of the linear stability analysis, where a high-frequency TS wave is damped by the forward facing smooth steps direct numerical simulation (DNS) is performed. The results of the DNS correlate favorably with the linear analysis and show that for the investigated high frequency TS wave, the K-type transition process is altered whereas the onset of the H-type transition is postponed. The results of the DNS suggest that for a high-frequency perturbation $\mathcal{F}=150$ and in the absence of other external perturbations, two forward facing steps of height 5\% and 12\% of the boundary layer thickness delayed H-type transition scenario and completely suppresses it for the K-type transition., Comment: 23 pages

Computational fluid dynamics is the test bed, for in-silico experiments, before a part is first built however the state-of-the-art relies on low-order Reynolds averaged Navier-Stokes (RANS) or Detached Eddy Simulations (DES) and their turbulence models that require fine tuning of many parameters. They are ill-suited for tackling the complex interaction between the wake of a Formula One front wing and the highly unsteady bluff-body wake of the rolling wheel. This thesis describes the effort made towards assessing the spectral/hp element LES as an alternative method for better for informing the process of the aerodynamicists. Results from the computation of the flow on a rounded wingtip give further insight into the complexity of the flow revealing numerous vortical structures merging into a trailing vortex. A direct numerical simulation of the unsteady wake of an idealised rolling wheel reveals the flow structures associated to the shedding at the top of the wheel, the symmetry breaking as well as the meandering of the jetting-vortices adding to our fundamental understanding of the wheel wake. In particular the DNS allows for a thorough survey of the wake structures in the immediate wake, less than half a diameter, both the jetting vortices and the shedding at the top of the wheel occur but experiments struggle to instrument. Finally preliminary results for the computation of the flow about the front-section of the MP4-17D are reported and compared to experimental results as well as state-of-the-art RANS computation. The CAD geometries, the mesh and initial conditions as well as the exact code used to run them are made openly available for each of the cases reported in this thesis for the fluids community to continue building on these results. Open Access

This work deals with the synthesis and physico-chemical study of heterobimetallic complexes bearing ruthenium(II)-tris-bipyridine units as photosensitizers covalently linked to a polypyridinic complex unit of iron (II) or cobalt (II), in order to investigate photoinduced electron transfer in such architectures.With bis-bipyridine type ligands, we synthesized a serie of tetranuclear complexes formed by a central complex unit FeII-tris-bipyridine, covalently linked to three RuII-tris-bipyridine subunits. Examination of their photophysical properties revealed a partial energy transfer between FeII subunit and excited state of RuII subunit, RuII*. This energy transfer can be easily short-circuited in presence of an external irreversible electron acceptor by an electron transfer process, leading to formation of RuIII species able to oxidize FeII subunit. By using a heteroditopic bipyridine-terpyridine type ligand, new trinuclear complexes bearing a central unit of FeII or CoII bis-terpyridine complex linked to two RuII-tris-bipyridine subunits were synthesized. This ligand confers to these architectures a more linear structure. In the case of the iron complex, purely intramolecular energy transfer can be short-circuited too, by electron transfer in presence of an external irreversible electron acceptor leading to the complete oxidation of FeII subunit. In the case of the cobalt complex, the photocatalytic cycle we considered implies formation of RuIII species via an electron transfer between RuII* and CoIII (previously electrogenerated) as electron acceptor. Nevertheless this reaction is fairly slow because the external electron donor used to regenerate RuII does not display a convenient irreversibility to prevent back electron transfer between CoII and RuIII.Finally, RuII and FeII electro- and photo-activable coordination polymers studies have been started. These types of polymers derive from the RuII and FeII trinuclear complex. They are obtained under soluble forms by the use of a heteroditopic bipyridine-bis-terpyridine type ligand, where the bipyridine part is complexed by RuII whereas addition of Fe2+ ions leads to the formation of polymers by a self-assembly process. Likewise RuII and FeII finished-dimension complex, photoinduced oxidation of FeII unit is possible even if its efficiency depends on the nature of the bridge between bipyridine and terpyridine units. Moreover, these polymers can be adsorbed as electroactive thin layers at the surface of an electrode (elaboration of modified electrodes) by a simple electrodeposition technique., Ce mémoire est consacré à la synthèse, à la caractérisation et à l'étude des propriétés électrochimiques et photophysiques dans l'acétonitrile de complexes hétérobimétalliques comportant des unités photosensibles du type ruthénium(II)-tris-bipyridine reliées de manière covalente à une unité polypyridinique de fer (II) ou de cobalt (II), dans le but d'étudier les transferts d'électrons photoinduits dans de telles architectures.A l'aide de ligands bis-bipyridine, une série de complexes tétranucléaires formés d'une unité centrale FeII-tris-bipyridine reliée à trois unités RuII-tris-bipyridine par une chaîne alkyle de longueur variable, a été obtenue. L'examen de leurs propriétés photophysiques met en évidence un transfert d'énergie partiel, intramoléculaire, de l'état excité des unités, RuII*, vers l'unité centrale FeII. Ce transfert d'énergie est court-circuité en présence d'un accepteur d'électron irréversible externe par un processus de transfert d'électron, qui conduit à la formation d'espèces RuIII capables d'oxyder la sous-unité FeII. En utilisant un ligand hétéroditopique de type bipyridine–terpyridine, de nouveaux complexes trinucléaires comportant une unité centrale FeII ou CoII bis-terpyridine reliée à deux unités RuII-tris-bipyridine ont également été synthétisés. L'utilisation de ce type de ligand confère à ces complexes une structure plus linéaire. Dans le cas du complexe de FeII, le transfert d'énergie purement intramoléculaire peut également être court-circuité par un transfert d'électron en présence d'un accepteur irréversible conduisant à l'oxydation quantitative de la sous-unité FeII. Dans le cas du complexe de cobalt, le cycle photocatalytique envisagé implique la photogénération de l'espèce RuIII via un transfert d'électron entre RuII* et l'unité CoIII (préalablement générée par voie électrochimique) qui joue le rôle d'accepteur d'électron. Toutefois cette réaction catalytique est relativement lente car le donneur d'électron utilisé pour régénérer le RuII ne possède par une irréversibilité suffisante pour concurrencer la réaction retour, c'est-à-dire la réoxydation de CoII par RuIII.Enfin, l'étude de polymères de coordination électro-et photo-activables de RuII et FeII a été abordée. Ce type de polymères dérive des complexes trinucléaires de RuII et de FeII. Ils sont obtenus sous forme soluble grâce à l'utilisation de ligands hétéroditopique de type bipyridine-bis-terpyridine, dont la partie bipyridine est complexée par le RuII, tandis que l'ajout de Fe2+ permet la formation du polymère par auto-assemblage. Comme pour les complexes de FeII et de RuII de dimensions finies, l'oxydation photoinduite de l'unité FeII est possible bien que son efficacité dépende de la nature du pont entre la bipyridine et les terpyridines. De plus, ces polymères ont pu être adsorbés sous forme de films minces électroactifs à la surface d'une électrode (élaboration d'électrodes modifiées) par une technique simple d'électrodéposition.

L'objet de la communication est une présentation des résultats et des perspectives du projet de coopération scientifique et technologique MAIA-Méthodes Avancées en Ingénierie mécAnique. Lancé en octobre 2003, il a pour cibles industrielles la propulsion et les équipements aéronautiques et spatiaux.

International audience; This paper deals with model reduction of assemblies of bladed disks. Some considerations about the use of the Fourier theory to describe the dynamics of assemblies of geometrically periodic structures are first recalled. This allows to define a set of spatially mono-harmonic solutions that are used to build the kinematic subspaces in a subsequent reduction process. The main characteristics of this sector substructuring technique are then presented and discussed. Finally, the proposed methodology is applied to an industrial rotor provided by Snecma to demonstrate its capability to handle large finite element models.

International audience; In this paper, we study the non-linear dynamics of a multi-stage system of bladed disks (turbomachinery) with friction dampers. Also, we focus on the forced response under multi-frequency excitations (quasiperiodic response). The analysis method consists in a multi-frequency harmonic balance method adapted to multistage cyclic structures. Numerical examples on an industrial structure are presented.; Dans cet article, nous abordons l'étude de la dynamique non-linéaire d'un ensemble multi-étages de roues aubagées (turbomachines) munies d'amortisseurs par frottement. On s'intéresse en particulier à la réponse forcée sous excitations multi-fréquentielles (régime quasi-périodique). La méthode d'analyse s'appuie sur une méthode de balance harmonique multi-dimensionnelle adaptée aux structures cycliques multi-étages. Des exemples numériques sur une structure industrielle sont présentés.

National audience; Les phénomènes qui affectent l’école – avancées du pédagogisme, subversion de la culture par l’hégémonie médiatique et de l’éducation par la dérive libérale – ne favorisent guère la demande de philosophie de l’éducation. Aussi celui qui l’enseigne peut-il plus que jamais apparaître, selon une image platonicienne, comme un pilote sur un bateau ivre. Comment il lui est néanmoins possible de défendre, dans ce contexte, une rationalité éducative est de réaffirmer la place du philosophe comme opérateur intellectuel de la cité, c’est ce que montre l’action de Bernard Jolibert au service de la pensée de l’éducation et de l’aventure philosophique dans sa diversité…

In the scheme of the French ETC Programme, we study Ihe modelling of ignition and combustion of propelling charges and offheir effects. In this paper, we evocate the evolution of the research performed. We analyse 460 cm3 manometric closed vessel test results to estimate combustion rates of several single base gun propellants, energy losses to the bomb wall and their possible models. The state of the theoretical background for models is presented. The experimental results are obtained with classic hot wire ignition and 20, 30 and 40 kJ plasma ignition. The analysis of these results shows less significant enhancement of apparent combustion rate than for double base propellant results we presented at 19fh ISB. We are developing an elementary global code which simulates these manometric closed vessel tests. This model takes into account the total volume itself and not yet the plasma torch and the vessel. The models tested for energetic flux arc based on simple physical principles as presented and applied to one classical single base propellant shot where the best fit with the experimental data is sought.