| Summary: | <p>This thesis presents a study on the hydrodynamics of a highly loaded tidal rotor designed for blockage using numerical models. First, the thesis presents a thorough evaluation of flow analysis methods for CFD simulations. This is a methodological review that enables a coherent and consistent study of axial-flow rotors with blade-resolved CFD simulations under different operational conditions including blade deformations, blockage, and transient flow effects.</p>
<p>Following the methodological assessment, a hydrodynamic analysis of a parametrically deformed axial-flow tidal rotor blade is discussed. The study shows the importance of blade deformations in rotor loads and performance. The hydrodynamics are decoupled by their twist and flapwise deformation components, with only the twist deformation effects successfully explained through two-dimensional blade-element theory. The hydrodynamic changes due to flapwise deformations, with a significant impact on loads and performance, are explained by changes in radial flow through the rotor and across the wake not considered in blade-element theory. These changes in flow induce an inboard load augmentation and an increase in near-tip load shedding, both affecting sectional lift and drag coefficients. The hydrodynamics of both deformation components are shown to be approximately independent of each other, which further enables an exploratory analysis of passive control strategies. Blade deflections as parts of passive control strategies are then shown as a potential alternative to active pitch control systems for tidal turbines.</p>
<p>The high-fidelity simulations were also used to evaluate the constituent parts of blade-element momentum (BEM) models. The simulation data was used to correct the empirical momentum function used at high-load regimes, significantly improving the predictive capabilities of a BEM model, whereas tip-loss correction models were identified as the most significant shortcoming in BEM modelling, greatly affecting the accuracy of the load and performance predictions.</p>
<p>The final part of the thesis evaluates the hydrodynamics of a catamaran-style floating tidal platform, designed to assess transient load effects on rotor blades. Using a seakeeping time-domain hydrodynamic model, coupled with a dynamic BEM model, which is verified through comparison with experiments and high-fidelity simulations, the floating tidal turbine was analysed under the combined effects of waves and currents. The result of this analysis highlights a non-linear interaction between waves, platform motions and loads, having a limited impact on average power and thrust but with a dramatic change in load fluctuations. The analysis highlights the challenges of operating floating tidal rotors near the free surface.</p>
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