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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Étude expérimentale d'un anneau tourbillonnaire en fluide newtonien et non newtonien en régime faiblement inertiel / Experimental study of a vortex ring in Newtonian and non-Newtonian fluids en régime faiblement inertiel

Bentata, Omar 20 February 2013 (has links)
Cette thèse est une étude expérimentale de la formation et de la maturation d’un anneau tourbillonnaire. Elle porte sur les écoulements faiblement inertiels (Reynolds : 5 à 500) en fluide newtonien puis non newtonien. Les anneaux sont générés par un système cylindre-piston. Ils sont analysés par visualisation et par vélocimétrie par images de particules (PIV). La dynamique en fluide newtonien à faible nombre de Reynolds se révèle plus complexe que celle à grands Reynolds avec l’apparition d’un anneau secondaire contrarotatif. Les résultats obtenus en fluide rhéofluidifiant montrent l’influence de l’indice de comportement ainsi que les zones de comportement rhéofluidifiant et newtonien. Les explorations en fluides viscoplastique et viscoélastique montrent la formation d’un ou plusieurs anneaux secondaires contrarotatifs, qui diffèrent dans leur formation et leur dynamique des anneaux observés en fluide newtonien et que l’on associe aux propriétés physiques intrinsèques du fluide. / The present work is an experimental study of the generation and the maturation of vortex rings, in order to characterize their structure and their global dynamics for small to moderate Reynolds numbers (between 5 and 500) in Newtonian and non-Newtonian fluids. The experimental set-up consists of a vertical cylindrical piston-tube system with the lower part immersed in a filled tank. Measurement campaigns have been carried out using dye visualization and Particle Image Velocimetry (PIV). A first part of the work is focussed on Newtonian fluid and allows the dynamics at low Reynolds numbers to be investigated qualitatively and quantitatively. This dynamics turns out to be more complex than the one classically observed at high Reynolds numbers, and is characterized by the production of a counter-rotating secondary vortex ring. The results obtained for shear thinning fluids show the influence of the power-law index on the development and the propagation of the ring. The computation of the shear rate field allows the results to be analyzed in terms of shear thinning and Newtonian regions. Finally a preliminary investigation for viscoplastic and viscoelastic fluids has been performed. In both cases, it is shown that one (for viscoplastic fluids) or several (for viscoelastic fluids) counter-rotating secondary vortex rings are generated, a phenomenon that can be associated with the intrinsic physical properties of the fluid. All these results provide several perspectives of study in the field of vortex rings dynamics in the weakly inertial regimes.

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