An axially symmetric water jet was designed and constructed to complement an existing air jet facility. The water jet operates at Reynolds numbers, based on nozzle diameter, up to 50,000. The jet is forced at high levels by a reciprocating Scotch yoke mechanism. By using an output signal from the Scotch yoke as a phase reference, it is possible to obtain either phase-locked hot film data or phase-locked photographs of the dye-marked coherent vortical structures in the shear layer. By assuming zero azimuthal velocity, continuity allows reconstruction of the vorticity field from the data obtained traversing the jet using a single straight hot film probe. Thus the phase-locked photographs and the phase-locked data sets can be compared. The close agreement of the reconstructed vorticity with the photographs gives credence to the assumption of zero azimuthal velocity, and shows that the dye injection method of flow visualization accurately represents the vortical structure of this flow.

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Half model testing is considered a valuable wind tunnel technique that offers many benefits over conventional full span testing. The technique suffers from aerodynamic losses due to flow separations on the model surfaces near the model/floor junction. Computational Fluid Dynamics, employing the Spalart-Allmaras turbulence model, and experimental investigations were carried out to evaluate the losses and to investigate the effect of localised suction on the junction flows. The wind tunnel model used was a rectangular and untwisted wing having a NASA LS(1)-0413 cross section and with a physical aspect ratio of 3. Tests were conducted at 10.00 incidence at a Reynolds number of 0.44 x 106. Aerodynamic performance of the wind tunnel half model was obtained by surface flow visualisation and pressure measurements on the wing surface in the junction region. CFD predictions showed significantly large losses compared to the experimental findings and therefore CFD predicted significant influence and benefits of suction. These were seen as elimination of the model surface separation and also recovery of the wing surface pressure distributions. In contrast to this, experiments showed much smaller separation than CFD without suction and applying suction in experiments, showed only a marginal effect on the flow separations, which also further deteriorated the pressure distributions. Future CFD studies on junction flows should be conducted using more advanced turbulence models such as Large Eddy Simulations (LES). In addition, to validate these CFD studies, velocity and turbulence measurements in the wing/floor junction region are also needed.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Wingtip vortices, created as a byproduct of lift, are both a hazard and a significant limiting factor in the increase of air traffic. In order to reduce separation distances between airplanes and increase safety, active flow control solutions are considered, however, more research is required to better understand the behavior of wingtip vortices. Therefore, this research focuses on the modification of the flow structure downstream using pulsed jets, visualization of the behavior of wingtip vortices using two dimensional particle image velocimetry, as well as measurements of the forces and moments affected by the pulsed jets using an aerodynamic balance. A NACA 0012 wing model equipped with two slots was mounted in a wind tunnel at approximately 150,000 Reynolds number. A valve system was designed to create jets of air at the wing tip in a steady or pulsed pattern from a slot placed either on the pressure side or the suction side. Particle image velocimetry measurements were taken at various distances downstream, and post-processed for the characterization of the vortex : position, angle, distance, vorticity contour, and circulation. Results indicate that the vortex can be forced into a cyclic pattern constrained between the baseline (no jet) vortex core position, and the position when the jet is permanently activated (steady blowing cases). Depending on the slot used, the vortex trajectory can be forced into an inclination angle. Steady blowing cases show near-sinusoidal oscillations, while pulsed blowing cases exhibit a steady rise in angle, with a slight oscillating pattern in displacement distance values. The circulation values are significantly changed, with a significantly higher dispersion than for the baseline case. Furthermore, the vortex core size is consistently larger as it is displaced away from the baseline case. Additionally, lift, drag and pitching moment were measured in a wind tunnel using an aerodynamic balance. Results showed that lift/drag coefficients consistent with published results, and that activating the jets on the pressure or suction side decreased lift. As instability grows, the destruction of the wingtip vortices occurs past the maximum downstream distance studied, therefore, additional PIV measurements should be taken further downstream. Moreover, supplementary PIV measurements at the slot themselves should be considered to better understand how the perturbed flow structure interacts with the pulsed jets.

The polar vortex is a large scale cyclone located in the middle atmosphere near to the planet’s geographic poles. These vortices form during the hemispheric winter and break down in the spring of the following year. They may also break down in mid winter, causing a sudden stratospheric warming event (SSW). The vortex is thought to be preconditioned leading up to these warming events, resulting in the breakdown of the vortex. Integral diagnostics are used to investigate the stripping of air from the vortex as part of this preconditioning. Contour diagnostics of mass and circulation are calculated using ERA-40 reanalysis data for the stratosphere. The edge of the vortex is easily identifiable in these diagnostics as a high gradient of Ertel’s potential vorticity (PV), and the warming events are also clearly visible. From these the amount of air removed from the vortex is determined from the balance equation of the mass integral. These terms show that there are significant amounts of air removed from the vortex, with several stripping events identifiable in them through the winter, especially in those during which a major sudden warming event occurred. These stripping events can be seen in corresponding PV maps, where tongues of PV can be seen to be stripped from the vortex and mixed into the surrounding surf zone of turbulent air. From the integral diagnostics a Lagrangian measure of the meridional circulation in the stratosphere is also calculated. In the final part of the thesis a shallow water model is used to investigate a quantitative link between forcing and the amount of stripping of the vortex. It is found that when the forcing is large enough there is significant stripping of mass from the vortex. This does not lead to SSWs in all cases, and the total amount of stripping is not found to be proportional to the maximum amplitude of the forcing.

Cette thèse porte sur la réalisation et l'étude de systèmes hybrides d'interface entre une couche magnétique et un supraconducteur. Tout d'abord, nous avons réalisé et étudié des structures magnétiques mésoscopiques dont les propriétés magnétiques ont été modulées par l'effet de la dimensionnalité du système (épaisseur et taille latérale). Deux types des structures ont été considérés. La première est constituée par des couches minces de pérovskite LaSrMnO. Par une étude complexe nous avons réussi à démontrer la corrélation directe entre l'incorporation de l'oxygène dans le LaSrMnO et l'évolution de ses propriétés structurales, magnétiques et électriques. Une deuxième classe de matériaux magnétiques étudiés est constituée des métaux de transition (Co) et des alliages (Ni80Fe20). Les couches ont étés structurées par lithographie optique et gravure ionique sous forme d'objets de taille micronique. Par la suite, ces structures ferromagnétiques ont été interfacées avec des films minces constitués d'un supraconducteur à haute température : YBaCuO. L'objectif ultime de cette étude a été le contrôle de la dynamique des vortex dans le supraconducteur par deux types de mécanismes: intrinsèque ou les centres de pinning sont les défauts structuraux dans le film supraconducteur et un mécanisme extrinsèque lié à l'influence des modulations du champ magnétique généré par la structure magnétique mésoscopique adjacente. / The present thesis deals with the fabrication and study of hybrid, ferromagnetic/superconducting, interface systems. Magnetic mezoscopic systems, whose magnetic properties were modulated by the dimensionality (thickness and lateral size) of the systems was studied. Two types of structures were considered. The first consisted of perovskite-like epitaxial LaSrMnO thin films. We have demonstrated the direct correlation between oxygen incorporation in the LaSrMnO lattice and the evolution of its structural, magnetic and electric properties. A second class of magnetic materials that has been studied consisted of transition metals (Co) and alloys (Ni80Fe20). We have defined micronic objects from the as-deposited films, by means of optical lithography and ion beam etching. These structures were then integrated to form an interface with thin epitaxial high Tc superconducting films: YBaCuO. The ultimate goal of the above studies was the control of vortex dynamics within the superconducting layer by two mechanisms: the first, intrinsic, in which flux pinning is achieved by structural defects within the superconducting film, and a second one, extrinsic, correlated with influence of the magnetic field modulations created by the adjacent mezoscopic magnetic structure.