A CFD Study on a Station Keeping Device for a Marine Current Turbine

The last two decades have witnessed a dramatic change in nation’s climate policies around the world toward a less carbon dependent energy production. This has given rise to a rapid expansion within the renewable energy sector and a wide range of alternative energy technology is in development and in use at this day. One of these upcoming technologies are the Marine Current Turbines (MCT’s) which are currently undergoing extensive research and testing in the UK.The purpose of this thesis was to investigate the performance of a novel mooring and station keeping device for a MCT in the form of a buoyant hydrofoil. The hydrofoil was designed to generate lift in the tidal stream in addition to its buoyancy and is therefore proposed to be a more efficient station keeping device than a submerged buoy.The analysis of the hydrofoil was done by steady- state computational fluid dynamics studies where several different geometrical configurations were compared in terms of the generated mooring angle. The devices were also evaluated in construction complexity and the ratio between generated buoyancy and lift. The study was divided into two parts where the first one was a 2D study aimed at determining the most suitable foil profile for the device. The second part of the thesis was devoted to finding the approximate dimensions for the hydrofoil using a 3D analysis setup.The findings showed that the most suitable foil shapes were the Joukowski and the NACA0025 profiles and the dimensions of the hydrofoil for a 10m diameter, 250kW turbine was 7m in chord length and 17m in width. The findings also showed that adding circular end plates to the NACA0025 geometry greatly improved its performance and gave a final mooring angle of 38.49 degrees.The findings in this thesis should be considered as a ‘proof of concept’ rather than accurate data to base critical design factors on. This is due to several constraints imposed partially by the limited processing power available and the lack of data from the turbulent flow conditions in tidal streams. A lot of research remains to be done before the concept is confidently proven to work in practice, but, according to the author, this thesis provides grounds that there is good reason to further the development of the concept.Validerat; 20121011 (anonymous