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In the modern advanced gas turbines, the turbine inlet temperature may exceed 1500°C as a requirement to increase power output and thermal efficiency. Therefore, it is imperative that the blades and vanes are cooled so they can withstand these extreme temperatures. Film cooling is a cooling technique widely used in high-performance gas turbines. However, the film cooling effectiveness has almost reached plateau, resulting in a bottleneck for continuous improvement of gas turbines' efficiency. In this study, an innovative cooling scheme, mist film cooling is investigated through experiments. A small amount of tiny water droplets with an average diameter about 10-15 µm (mist) is injected into the cooling air to enhance the cooling performance. A Phase Doppler Particle Analyzer (PDPA) system is used for droplet measurements. Mist film cooling performance is evaluated and compared against air-only film cooling. This study continues the previous work by (a) adding fan-shaped holes and comparing their cooling performance with the round holes, (b) extending the length of the test section to study the performance farther downstream the injection holds, and (c) using computational simulation to investigate the feasibility of transporting mist to the film cooling holes through gas turbine inside passages. The results show that, with an appropriate blowing ratio, the fan-shaped holes performs about 200% better than round holes in cooling effectiveness and adding 10% (wt.) mist can further enhance cooling effectiveness 170% in average. Farther downstream away from the injection holes (X/D> 50), mist cooling enhancement prevails and actually increases significantly. PDPA measurements have shed lights to the fundamental physics of droplet dynamics and their interactions with thermo-flow fields. These experimental results lead to either using lower amount of cooling air or use fewer number of cooing holes rows. This means higher gas turbine power output, higher thermal efficiency, and longer components life which will reflect as a cheaper electricity bill. Computational Fluid Dynamics (CFD) showed that it is feasible to transport the water mist, with initial diameters ranging from 30 µm-50 µm and mist ratio of 10-15%, to the cooling holes on the surface of the turbine vanes and rotors to provide the desired film cooling. Key words: Gas Turbines, Heat Transfer, Film / mist Cooling, Experimental Study, Mist Transport, CFD, PDPA.

Francisella tularensis is a highly virulent, intracellular pathogen that causes the disease tularaemia. Francisella species contain a cluster of genes referred to as the Francisella pathogenicity island (FPI). Several genes contained in the FPI encode proteins needed for the intracellular growth and virulence of Francisella tularensis. Pathogenicity determinant protein A (PdpA), encoded by the pdpA gene, is located within the FPI and has been associated with the virulence of Francisella species. The experiments outlined in this dissertation examine the properties of PdpA protein expression and localization as well as the phenotypes of non-polar F. novicida pdpA mutants. Monoclonal antibody detection of PdpA showed that it is a soluble protein that is upregulated in iron-limiting conditions and undetectable in an mglA or mglB mutant background. Deletion of pdpA resulted in a strain that was highly attenuated for virulence in chicken embryos and mice. The ΔpdpA strain was capable of a small amount of intracellular replication but, unlike wild-type F. novicida, remained associated with the lysosomal marker LAMP-1, suggesting that PdpA is necessary for progression from the early phagosome phase of infection. Infection of macrophages with the ΔpdpA mutant generated a host-cell mRNA profile distinct from that generated by infection with wild type F. novicida. The transcriptional response of the host macrophage indicates that PdpA functions directly or indirectly to suppress macrophage ability to signal via growth factors, cytokines and adhesion ligands. Experiments were designed to mutagenize a putative F-box domain within the amino terminus of PdpA. Deletion of amino acids 112-227 created a strain which was impaired in intracellular replication and exhibited severely reduced virulence. However, alanine mutagenesis of key conserved leucine residues required for the interaction of F-box domains with host proteins had no observed effect on bacterial growth in macrophages and did not affect virulence in chicken embryos or mice. Mono and polyubiquitinated proteins associated with both the wild type F. novicida and ΔpdpA bacterial strains early during the infection of J774A.1 macrophages. After 1 hour of infection the wild type strain developed a more intimate association with mono and polyubiquitinated proteins whereas the ΔpdpA strain did not. Inhibition of the host cell proteasome during infection did not affect the intracellular growth of wild type F. novicida. PdpA research concludes by examining the secretion patterns of F. novicida. PdpA was not detected as a surface exposed protein using biotinylation whereas IglA, IglB and IglC were found to be surface exposed in both wild type and ΔpdpA backgrounds. These observations suggest that PdpA is not involved in the assembly or function of the Francisella secretion system. FLAG tagged PdpA protein could not be detected in the TCA precipitated supernatant of broth grown cultures or in the immunoprecipitated cytosol of infected macrophages suggesting that PdpA is not a secreted protein.

Cette étude porte sur le transfert thermique entre un bain d'HeII pressurisé et un écoulement forcé d'HeII diphasique. Nous avons confirmé des résultats précédents ayant mis en évidence une amélioration de l'échange thermique à forte vitesse de vapeur par rapport à celui attendu. Nous sommes en mesure d'expliquer cette amélioration par la présence d'un film liquide de quelques microns sur les parois, mesuré par une sonde capacitive pariétale. En parallèle, nous avons détecté et caractérisé un brouillard de gouttes qui apparaît également à forte vitesse de vapeur. A partir de cette caractérisation, nous avons tenté d'estimer la puissance frigorifique fournie par les gouttes heurtant la paroi, pour la comparer aux non-linéarités observées du transfert thermique. Cette approche suggère que c'est bien le brouillard qui conduit à la formation du film en paroi, même si, faute d'un modèle complet de dépôt des gouttes, nous ne pouvons confirmer définitivement ce scénario.

L'objectif de recherche développé dans cette thèse est d'initier une méthode de conception des dispositifs de captage des polluants d'usinage basée sur la prédiction par simulation numérique des écoulements d'air et de particules induits par les machines tournantes.<br />La recherche des modèles numériques les mieux adaptés aux écoulements rencontrés s'est conduite en deux étapes. Sur la base de recherches bibliographiques et d'expérimentations numériques, la première étape démontre l'intérêt et la faisabilité de la simulation des grandes échelles sous-résolue en paroi (ou VLES pour Very Large Eddy Simulation), couplée au suivi lagrangien de particules, pour modéliser les écoulements diphasiques d'usinage, et rendre compte finement de l'interaction particules-turbulence.<br />Dans la seconde étape, une importante campagne expérimentale, menée sur un banc d'essai original représentatif d'une opération d'usinage, sert de base pour valider définitivement les modèles retenus. Dans le dispositif réalisé, un jet de particules stable et de débit contrôlé est créé en poussant dans une buse des microbilles de verres sphériques contre un cylindre en rotation. L'écoulement de la phase particulaire dans le banc d'essai est caractérisé par analyseur de particules phase Doppler (PDPA), et le champ de vitesse de la phase gazeuse par vélocimétrie par image de particules (PIV), cette dernière technique nécessitant le développement d'un code spécifique pour discriminer les phases en présence.<br />La comparaison des mesures et des résultats de simulation ouvre des perspectives nouvelles concernant l'applicabilité industrielle de la simulation des grandes échelles aux écoulements multiphasiques.