L’écoulement entre deux cylindres coaxiaux, appelé l’écoulement de Couette-Taylor, a été étudié lorsque le cylindre intérieur tourne. Quatre dispositifs ont été utilisés avec différentes tailles d’entrefer. Les visualisations montrent l’évolution des motifs avec le nombre de Reynolds, Re. La variation du couple sur le cylindre intérieur a été déterminée en utilisant le pseudo-nombre de Nusselt, qui est une mesure du taux de dissipation d’énergie.Pour des faibles valeurs de Re, l’écoulement est laminaire et azimutal, et le couple est proportionnel à Re. Au-delà d’une valeur critique de Re, les rouleaux de Taylor apparaissent et la pente de variation du couple change brutalement. Pour de grandes valeurs de Re, les rouleaux deviennent turbulents et la pente du couple augmente à cause de la dissipation d’énergie turbulente. Le couple a été mesuré jusqu’à Re=45.000 et montre une dépendance avec le rapport de rayons des cylindres et du nombre de vortex. Avant le régime ultime de la turbulence, les états avec plus de rouleaux présentent un couple plus grand et la situation est inversée dans le régime ultime.Une étude du couple agissant sur le cylindre intérieur a été menée en présence d’un liquide viscoélastique contenant des polymères de grande masse molaire. En appliquant des cycles d’accélération-décélération de la rotation du cylindre intérieur, le couple présente une boucle d’hystérèse dont l’aire augmente avec la concentration de polymère. Les statistiques des fluctuations de la turbulence élastique ont été analysées. Le couple exercé par les vortex solitaires obtenus lors de la phase de décélération, avant la relaminarisation complète de l’écoulement, a été étudié. / The flow between two concentric cylinders, i.e., the Couette-Taylor flow, has been investigated when only the inner cylinder rotates. Four set-ups have been employed with 4 values of the radius ratio. Flow visualisations have been performed to analyse the evolution of the flow patterns with the Reynolds number, Re. The variation of the torque acting on the inner cylinder with different parameters has been quantified using the pseudo-Nusselt number, which measures the rate of energy dissipation in the flow.At low Re, the flow is laminar and azimuthal, and the torque is proportional to Re. Above a critical value of Re, Taylor vortices emerge in the flow and the slope of the torque changes drastically. At high values of Re, the vortices become turbulent and the increase rate of torque is enhanced due to the energy dissipation of turbulence. The torque measured up to Re=45 000 depends on the radius ratio of the cylinders and on the number of vortices. Below the ultimate regime of turbulence, flows containing larger number of vortices exert larger levels of torque; above it, flows containing larger number of vortices exert lower levels of torque.A specific study of the torque exerted on the inner cylinder has been carried out with viscoelastic fluids made of large-weight-molecule polymers. If acceleration-deceleration cycles of the rotation of the inner cylinder are applied, the torque exhibits a hysteretic loop, which increases with the polymer concentration. The statistics of the elastic turbulence fluctuations have been analysed. A special focus was made on the torque induced by the solitary vortices obtained in the deceleration phase, before the flow relaminarisation.

Made available in DSpace on 2014-12-17T14:58:19Z (GMT). No. of bitstreams: 1 FernandoNS_DISSERT.pdf: 5044327 bytes, checksum: 66e88407297dda873c6a6d882b6de312 (MD5) Previous issue date: 2012-08-27 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / A batch of eighty-four coupons of low carbon steel were investigated at laboratory conditions under a corrosive, cavitative-corrosive (CO2) and corrosive-erosive (SiO2 + CO2) in an aqueous salt solution and two levels of temperature. The following measurements were made on Vickers (HV0,05, HV0,10, HV0,20) Microhardness tests at three levels of subsurface layer. A turbulent flow collided on the cylindrical sample, with and without mechanical stirring and gas bubbling, with and without fluid contamination by solid particles of SiO2, at two temperatures. Surface Roughness and Waviness, under two conditions "as received, after machining" and "after worn out", as well as gravimetric and electrochemical parameter were measured on the two opposite generatrices of each cylindrical sample, on the flow upstream (0?) and downstream (180?) by Profilometry, Mass Variation and Linear Polarization Resistance (LPR). The results of the Microhardness and Surface Texture of all coupons were subjected to statistical comparison, using the software Statgraphics? Centurion XVI, 95% statistical certainty, and significant differences were observed in some arrays of measurements. The corrosive wear rate measured by LPR and mass variation shown to be sensitive to the presence of bubbles and hydrodynamic fluctuations inside the cell, considering the temperature and contamination of corrosive fluid by solid particles. The main results of visual inspection relative to some topologies of the surface damages involving different mechanisms that were seen to give explanation for some fluctuations in wear rates of the steel experimentally investigated / Um lote de oitenta e quatro corpos-de-prova (CP) de a?o AISI 1018 foi investigado em laborat?rio sob solicita??es corrosivas, cavitativo-corrosivas (CO2) e erosivocorrosivas (SiO2+CO2) em meio aquoso salino e a duas temperaturas. Foram realizados ensaios de microdureza Vickers a tr?s n?veis de subsuperf?cie (HV0,05, HV0,10, HV0,20). Um fluxo agitado colidiu contra os CPs, em todas as condi??es de ensaio, sem e com agita??o mec?nica e borbulhamento de g?s, sem e com contamina??o do fluido por part?culas s?lidas de SiO2, nas duas temperaturas estudadas. A rugosidade e ondula??o superficial, nas condi??es como recebidos, ap?s usinagem e ap?s desgastados , bem como medi??es gravim?tricas e eletroqu?micas foram realizadas em duas geratrizes opostas de cada corpo-deprova, a montante (0?) e a jusante (180?), atrav?s das t?cnicas de perfilometria, varia??o m?ssica e resist?ncia de polariza??o linear (RPL). Os resultados da microdureza e da textura superficial em todos CPs foram submetidos ? compara??o estat?stica, utilizando-se o software Statgraphics? Centurion XVI e, com 95% de certeza estat?stica, diferen?as significativas foram observadas em alguns grupos de medidas. As medidas das taxas de desgaste corrosivo, por RPL e por varia??o m?ssica, demonstraram serem sens?veis ? presen?a de bolhas e ?s flutua??es hidrodin?micas no interior da c?lula, consideradas a temperatura e a contamina??o do fluido corrosivo por part?culas s?lidas. Apresentam-se, tamb?m, os principais resultados da inspe??o visual em que se evidenciam algumas topologias do dano superficial nas geratrizes a 0? e a 180?, involvendo diferentes mecanismos que foram presenciados, para justificar algumas flutua??es nas taxas de desgaste do a?o em estudo