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Duct optimization for a ducted vertical axis hydro current turbine Alidadi, Mahmoud

Abstract

Turbines developed for the power production from the energy of tidal and river currents are commonly referred to as hydro current turbines. This research focuses on duct optimization for a ducted vertical axis hydro current turbine. As a first step, a discrete vortex method, referred to as “DVM”, is developed for the performance analysis of unducted vertical axis turbines. It is shown that the loads for an unstalled blade of a vertical axis turbine may be adequately approximated by a quasi-steady component and a pitching component. A new approach is developed for the calculation of nascent vortex position relative to the blade. Besides, a new approach is developed to take into account the effects of connection point between a blade and its supporting arm. Subsequently, a new numerical model, referred to as “BEM-DVM”, is developed for the performance calculation of ducted vertical axis turbines by combining a boundary element method referred to as “BEM” with the DVM model. Comparison of the results for unducted and ducted turbines showed that ducting significantly improves the power coefficient of a vertical axis turbine. In addition, the results showed that ducting decreases the torque fluctuations significantly, especially at high tip speed ratios. Based on the method developed for ducted turbines, a new approach is developed to calculate the effects of towing tank wall on experimental results. The results showed that the power coefficient of a turbine increases when it operates in a tank. This is especially true for a ducted turbine which has a higher blockage ratio than the unducted turbine in the tank. The results also showed that the amount of increase in power coefficient grows when the tank width decreases. An optimization study is conducted to find the duct shape that maximizes the output power of a vertical axis turbine. The optimized ducts results showed a higher power coefficient for the turbine relative to the results of experimentally tested ducts. It is also shown that there is an upper limit to the amount of increase in power coefficient due to ducting.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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