The shape of bridge deck sections used for long-span suspension bridges has evolved through the years, from the compact box deck girders, to twin box and multi-box decks sections, which proved to have better aerodynamic behaviour, and to bring economic advantages on the construction material usage side. This thesis presents a study of a new type of multi-box bridge deck for the Megane Bridge, consisting of two side decks for traffic lanes, and two middle decks for railway traffic, connected using stabilizing beams. Aerodynamic static force coefficient measurements were performed on a section model with a scale of 1:80, for Reynolds numbers up to 5.1 × 105 under angles of attack from -10° to 10°. Also there-dimensional CFD simulations were performed by employing a Large Eddy Simulation (LES) algorithm with a standard Smagorinsky subgrid-scale model, for Re = 9.3 × 107 and angles of attack 𝛼= -4°, -2°, 0°, 2° and 4°. The experimental and numerical results were compared with respect to accuracy, sensitivity, and practical suitability. Furthermore, the aerodynamic character for each individual decks including static coefficients, wind flow pattern and pressure distribution were studied through CFD simulation. ILS (Iterative Least Squares) method was applied to extract the flutter derivatives of Megane section model based on the results obtained from free vibration tests for evaluating the flutter stability. A comparison of the flutter derivatives was carried out between bridges with different deck configurations and the results are included in this thesis.

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This thesis presents the numerical and analytical study of the aerodynamic and heat transfer in laminar subsonic cascades along with the development of design guidelines and procedures to improve the design of microfabricated multistage radial turbines operating at low Reynolds number. Numerical analysis was performed on 24 cascade geometries using 2D computational fluid dynamics (CFD) for over 100 flow conditions for each cascade. Two dimensional correlations were extracted from CFD for profile and mixing losses, deviation and heat transfer. These correlations include Reynolds number and compressibility effects, and take into account incidence and various geometrical parameters (solidity, stagger, blade angles, thickness and mean-line distribution). Adaptation of losses to account for three dimensional effects and correlation for blockage were derived from analytical relationships. A turbomachinery simulation software based on mean-line analysis and conservation of rothalpy incorporating the developed correlations was programmed. The software can be adapted as for the physic it uses and the turbine configuration it analyses (axial, radial inward or outward, single or multi stage). The pressure profiles obtained from simulation were found to be in good agreement with experimental data for cold turbine tests. Design guidelines and charts are provided as well as cycle analysis considering microfabrication limitations. A considerable increase in stage isentropic efficiency compared to previous devices can result from the use of slender blades, lower solidity cascades and aspect ratios of 0.5, suggesting efficiencies as high as 85% for Re > 700. The study shows that higher power density and multistage matching can be achieved through the radial outward configuration. Two designs are presented, a single stage turbine for the next generation of microturbopump prototype and a turbine configuration with four rotors and 10 stages for closed Rankine cycle providing 50.7 W of net mechanical power.

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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.