Experimental and numerical hydrodynamic analysis of a novel tidal turbine : the Hydro-Spinna

Abstract

Energy security, economic growth and mitigation of climate change have been driving factors in the development and deployment of renewable energy technologies. Tidal power is one such technology and includes both tidal barrages and grid connected marine current turbines although among the latter grouping, devices have yet to go beyond the prototype phase. A novel horizontal marine current turbine, “The Hydro-Spinna”, is introduced in this thesis. The basic geometry of the turbine is defined by some key parameters and their influences on the operation of the device are studied using numerical and experimental methods. Firstly, the performance of the Hydro-Spinna at different pitch to diameter ratio (P/D) was investigated using a numerical model. It was found that a turbine with low P/D performed better than one with a higher value, with a maximum Power Coefficient (CP) of 0.32 at optimal Tip Speed Ratio (TSR) of 2.25. The power characteristic of the turbine was further investigated with different blade profiles where there was little variation in power generated, indicating that the P/D is a more significant turbine parameter than the blade profile for this particular turbine. Experimental investigations conducted in a towing tank indicated that the turbine can operate with little dependency on the immersion depth. It was also determined that the Hydro-Spinna was able to operate at a half-submerged condition i.e. with half the turbine above the water surface. Finally, the cavitation and Underwater Radiated Noise (URN) characteristics of the Hydro-Spinna turbine were measured in a cavitation tunnel and analysed; the Hydro-Spinna was generally found to operate cavitation free and even in extreme conditions, only tip vortex cavitation was observed. The model scale URN levels measured was scaled up the full-scale and the data compared to a representative reference level recommended by ICES for fisheries research. In normal operating conditions for the turbine, the URN was predicted to be below the acceptable threshold level.