This thesis proposes equations extending the Free Surface Actuator Disc Theory to yield drag forces and interference factors from a series of two porous discs in open channel flows. The new model includes blockage ratio and Froude number as independent variables, which are inferred in advance to yield a single solution in the prescribed domain. The theoretical extension is integrated with the Blade Element Theory in a Double Multiple Streamtube model (DMS) to predict axial loads and the performance of confined Darrieus turbines. The turbine thrust force influences the flow approaching the rotor. Hence, a momentum method is applied to solve the hydraulic transition in the channel, achieving the unknown inflow factor from the undisturbed flow imposed downstream. The upstream blockage ratio and Froude number are thus updated iteratively to adapt the DMS to subcritical applications. The DMS is corrected further to account for the energy losses due to mechanical struts and turbine shaft, flow curvature, turbine depth, and streamtube expansion. Sub-models from the literature are partly corrected to comply with the extended actuator disc model. The turbine model is validated with experimental data of a high-solidity cross-flow hydrokinetic turbine that was previously tested at increasing rotor speeds. Turbine arrays are investigated by integrating the previous turbine model with wake sub-models to predict the plant layout maximizing the array power. An assessment of multi-row plants shows that the array power improves with closely spaced turbines. In addition, highly spaced arrays allow a partial recovery of the available power to be exploited upstream by a new turbine array. The highest array power is predicted by simulations on different array layouts considering constant array blockage ratio and rotor solidity. Finally, assuming a long ideal channel, the deviation in the inflow depth is speculated to become asymptotic after many arrays, implying almost identical power conversion upstream.

Road and railways tunnels are constructed for decreasing the transportation time inside city or intercity. The fire safety systems are mounted for the safe use of tunnels. Therefore, it is important to accurately predict the fire-induced air velocity,temperature and smoke concentrations in tunnel fires in order to design efficient fire protection systems. To this end, scaled tunnel models are used and experiments are carried to understand the phenomena on these tunnel models. In addition, the studies for investigating the tunnel fire phenomena and their methods of modeling techniques for fire experiments are mentioned. In the literature, there is no sufficient information about vehicles&#039 / blockage effect on heat release rate and temperature distribution inside tunnel with different ventilation velocities. As a result, in order to research this subject, the scaled model tunnel is constructed in Fluid Mechanics Laboratory. Based on the Froude number scaling, wood sticks with different configuration inside the model tunnel are burned in a controlled environment. The heat release rate measurement, sampling of gases after combustion, mass loss rate of burning models and temperature distribution along the tunnels with different longitudinal ventilation velocities are measured to investigate the effect of different cross-sectional areas of the burning substances. Furthermore, the model vehicles having a square base area are built according to wood crib theory. The results are investigated with statistical techniques called &quot / Analysis of Variance&quot / and general results have been tried to be reached. It is determined that the variation of air velocity inside tunnel is not so effective, but model vehicle&#039 / s cross sectional area is directly proportional to heat release rate.

Un corps en chute libre dans un fluide sous l'effet de la gravité peut être soumis à des perturbations. De façon générale, celles-ci peuvent être dues aux mouvements propres du fluide porteur, à la présence d'autres corps mobiles ou encore à la présence de parois. Dans un premier temps, nous avons choisi de nous intéresser à l'interaction de deux disques identiques chutant dans un fluide de densité proche de celle du corps. Différents comportements d'interaction sont observés pour des disques de rapports de forme variable (diamètre sur épaisseur) et des nombres de Reynolds (effets inertiel sur effets visqueux) couvrant des trajectoires rectilignes et périodiques oscillantes. Lorsque les disques sont lâchés en tandem, ils s'attirent et se rencontrent. Après le contact, le comportement dépend du rapport de forme : les disques épais se séparent et tombent côte à côte, tandis que les disques minces continuent leur évolution ensemble dans une configuration relative stable. Lorsque les corps sont lâchés côte à côte, on observe une répulsion des corps qui se traduit par un éloignement horizontal. Une modélisation pour chacun de ces comportements (attraction, répulsion) a été proposée. Dans un deuxième temps, nous avons étudié l’effet de parois fixes sur le mouvement d'un disque isolé en chute libre. Les disques sont lâchés dans des tubes cylindriques créant différents rapports de confinement (diamètre du disque sur diamètre du tube). Nous avons mis en évidence que le comportement du corps dépendait du rapport de forme : la trajectoire d'un disque mince est déstabilisée par le confinement, alors que celle d'un disque épais est stabilisée. Des visualisations des sillages à l'aide de colorants ainsi que des simulations numériques de l'écoulement autour de disques fixes ont été réalisées et ont permis de mieux comprendre le rôle du sillage sur les interactions / A body falling in a fluid under the effect of gravity may be perturbed by the presence of other bodies or fixed boundaries. We first focused our attention on the interaction of two identical disks in freefall. We investigated the kinematics of disks with different aspect ratios (ratio of diameter to thickness) and with different initial relative positions, for a range of Reynolds numbers (ratio of inertial effects to viscous effects) covering both rectilinear trajectories and periodic, oscillating trajectories. When the disks are falling in tandem, the trailing body accelerates until it catches up the leading one. After the contact, the behaviour depends on the aspect ratio. Thicker disks separate and fall side by side and separated while thinner disks continue their fall together in Y or T reversed position. A model of the different types of interaction (entrainment by the wake and horizontal repulsion) is proposed. The second part of the study is devoted to the effect of fixed walls on the kinematics of freely falling bodies. The behaviour again depends strongly on the aspect ratio : a thin disk is destabilized when the blockage ratio (ratio of disk diameter to tube diameter) increases, whereas thicks disks are stabilized. In addition, visualizations of the wakes using dyes and numerical simulations for fixed disks were performed and provide a better understanding of the role of the wake in the interaction

Les caractéristiques des transferts de masse et de chaleur par convection forcée lors de l'évaporation du film liquide dans le canal en présence d'un cylindre carré poreux parcouru par un écoulement transversal sont étudiées numériquement. L'objectif principal de la présente étude est d'évaluer l'effet de l'introduction d'un cylindre carré poreux sur le transfert de chaleur et de masse. Plus précisément, cette étude examine l'influence de paramètres tels que l'humidité relative de l'air ambiant, la température de l'air à l'entrée, le flux de chaleur imposé, la position du cylindre, le taux de blocage et le nombre de Reynolds. Une comparaison entre les deux configurations, avec et sans cylindre carré poreux a été réalisée pour mettre en évidence l'effet de son ajout. Pour modéliser ce phénomène nous avons résolu l'équation classique de convection forcée et le modèle de Darcy-Brinkman-Forchheimer dans les milieux poreux. Nous avons trouvé que l'insertion d'un cylindre carré poreux dans le canal pourrait perturber l'écoulement et améliorer de manière significative les taux de transfert de masse et de chaleur au niveau des parois du canal. Les transferts de chaleur et de masse deviennent plus importants avec la diminution du nombre de Darcy et lorsque l'obstacle poreux est placé au milieu du canal. Par contre, l'augmentation de l’humidité relative de l’air ambiant et de la température d'entrée réduit le transfert de masse. A Da = 10-6, l'écoulement ne pénètre plus à travers le cylindre poreux, la structure de l'écoulement est similaire à celui d'un cylindre carré plein. Enfin, nous proposons des lois de corrélations qui permettent de prédire les valeurs des nombres de Sherwood et de Nusselt en fonction des nombres de Reynolds, de Biot et du taux de blocage. / The characteristics of mass and heat transfers by forced convection during liquid film evaporation in the channel with a built in porous square cylinder in a cross flow are investigated numerically. The main objective of the present study is to evaluate the effect of introducing a porous square cylinder on the heat and mass transfer. Specifically, this study examines the influence of parameters such as the relative humidity of the ambient air, the air inlet temperature, the imposed heat flux, the variation of the cylinder position, blockage ratio and Reynolds number on the performance of the evaporation at the channel wall. A comparison between the two configurations, with and without, porous square cylinder has been performed to highlight the effect of its addition. To achieve this, we solved the classic equation of forced convection and the Darcy-Brinkman-Forchheimer model in the porous media. We find that the insertion of a porous square cylinder in the channel could make the flow more disturbed and significantly improve mass and heat transfer rates at the channel walls. The heat and mass transfer enhancements is greater with a decrease of the Darcy number and for γ=1 when the porous obstacle is placed in the middle of the channel. It is also greater with a decrease of the temperature and relative humidity of the air at the inlet. At Da = 10-6, the flow does not penetrate through the porous cylinder, the flow pattern is similar to that of a solid square cylinder. Finally, we propose correlations that allow us to define the Sherwood and Nusselt numbers based on the Reynolds, Biot numbers and the blockage ratio.

Anthropogenic climate change is approaching predicted tipping points and there is an urgent need to de-carbonize energy systems on a global scale. Generation technologies that do not emit greenhouse gas need to be rapidly deployed, and energy grids need to be updated to accommodate an intermittent fluctuating supply. Rapidly advancing battery technology, cost reduction of solar and wind power and other emerging generation technologies are making the needed changes technically and economically feasible. Extracting energy from fast-flowing tidal currents using turbines akin to those used in wind farms, offers a reliable and predictable source of GHG free energy. The tidal power industry has established the technical feasibility of tidal turbines, and is presently up-scaling deployments from single isolated units to large tidal farms containing many turbines. However there remains significant economic uncertainty in financing such projects, partially due to uncertainty in predicting the long-term energy yield. Since energy yield is used in calculating the project revenue, it is of critical importance. Predicting yield for a prospective farm has not received sufficient attention in the tidal power literature. this task has been the primary motivation for this thesis work, which focuses on establishing and validating simulation-based procedures to predict flows through large tidal farms with many turbines, including the back effects of the turbines. This is a challenging problem because large tidal farms may alter tidal flows on large scales, and the slow-moving wake downstream of each rotor influences the inflow to other rotors, influencing their performance and loading. Additionally, tidal flow variation on diurnal and monthly timescales requires long-duration analysis to obtain meaningful statistics that can be used for forecasting. This thesis presents a hybrid simulation method that uses 2D coastal flow simulations to predict tidal flows over long durations, including the influence of turbines, combined with higher-resolution 3D simulations to predict how wakes and local bathymetry influence the power of each turbine in a tidal farm. The two simulation types are coupled using a method of bins to reduce the computational cost within reasonable limits. The method can be used to compute detailed 3D flow fields, power and loading on each turbine in the farm, energy yield and the impact of the farm on tidal amplitude and phase. The method is demonstrated to be computationally tractable with modest high-performance computing resources and therefore are of immediate value for informing turbine placement, comparing turbine farm-layout cases and forecasting yield, and may be implemented in future automated layout optimization algorithms. / Graduate