The applicability of aerodynamic models to tidal turbines.
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For the tidal current power industry to progress, simple models for predicting the performance of tidal current turbines are needed. Currently the aerodynamic models developed for wind turbines are typically used to predict tidal turbine performance. There are a number of significant differences between wind and tidal turbines so these models will not provide a good representation of tidal turbine performance. The main aim of this project was to show the magnitude of the differences between wind and tidal turbine performance caused by dissimilarities in wind and tidal turbine operation. Two main areas were investigated: the effects of energy extraction on flow speeds and the effect of the proximity of the boundaries. An analytical model was developed which allowed the effect of the number of turbines at a site on the performance of each turbine to be investigated. The magnitude of the change in performance was found to depend on the design and geometry of the turbines and the drag coefficient of the site. The model results indicated that, typically, there will be no noticeable reduction in the power generated by single or small farms of turbines, but installing large farms of turbines will cause significant reduction in the power generated per turbine. An analytical model was developed which allowed the effects of blockage on performance to be investigated. Applying the model to a single turbine in the Sound of Islay indicated that the performance of a realistically sized turbine in an actual tidal channel will differ from that predicted by an aerodynamic model. The effect of the proximity of the turbine to channel boundaries was investigated and performance was found to decrease as the free surface was approached. In all of the areas investigated the performance tidal turbines has been found to differ significantly from the performance predicted by aerodynamic models. This implies that it is not appropriate to use aerodynamic models to predict tidal turbine performance.