On flow fluctuation's impact on the performance of vertical axis turbines-A potential flow analysis
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During the last decade, with rapidly increasing deployment of tidal current turbine prototypes in many countries, a number of failures have been reported. Several of these failures were attributed to the intensive flow fluctuation around the device. As a result, designers had to re-design their devices although no initial design stage approach is available yet. In this paper, we derive a formulation to quantify the relationship between the power output fluctuation and the flow fluctuation with a newly defined power fluctuation coefficient. Particularly, it includes various turbine design parameters. It suggests that the turbine fluctuation coefficient is proportional to the solidity and the square root of the tip speed ratio. For a curved-blade turbine, the relationship between the blade span length and the maximum radius is critical. Furthermore, we present a procedure to identify the impact of wake vortices on the turbine blade, from which they shed. The results obtained from both the formulation and the above procedure show good agreement with those obtained from the experimental test and expensive numerical tools, but the current formulation and procedure cost much less. They are expected to provide guidance and assistance to turbine design at the initial design stage and can also be applicable to the vertical axis wind turbine design. Published by AIP Publishing.