| Summary: | 碩士 === 國立交通大學 === 機械工程學系 === 99 === A new type of vertical-axis wind turbine is developed in this project. This new design combines the merits of the lift type and drag type of wind turbines. It also possesses a feature by which several turbine wheels can be stacked together to get higher output power. The method of computational fluid dynamics is mainly used to investigate the flow structure and aerodynamic characteristics, also conducted is the experimental work to validate the numerical simulation. The numerical scheme is based on a finite volume method. The multiple reference frames (MRF) is adopted to tackle the rotation of the turbine wheel. To simplify the complicated problems, the quasi-unsteady state is assumed so that the wind turbine is fixed at a number of specified angular positions and unsteady computations are undertaken.
It is obtained from the simulation that the resulted torque is related to the angular speed of the wind turbine in a linear decreasing fashion, a quadratic function of the wind velocity and a cubic function of the diameter of the wind turbine. After non-dimensionalization, the resulting moment coefficient becomes a linearly decreasing function of the tip speed ratio. It can be derived from this relationship to show that the power coefficient is a quadratic function of the tip speed ratio and, furthermore, to find the maximum power coefficient and the optimum tip speed ratio. It is also shown that by using the fully unsteady model, in which the wind turbine continuously rotates in the simulation, the above correlations are still valid. However, comparing with the quasi-unsteady calculations, the resulting moment coefficient and power coefficient are much higher. The experimental results lies in between of the fully unsteady and quasi-unsteady predictions. For the quasi-unsteady on calculations, the effect of inertia is not property accounted for. As for experiments, the experimental rigs are too rough and there are a lot of uncertainties about the measurements, cause the experimental inaccuracy.
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