Study On Energy Capture Characteristics Of Vertical-axis Tidal Turbine

With the continuous development of society and economy, the demand for energy is growing.The traditional fossil energy is not only non-renewable, but also causes serious environmental pollution, so the development and utilization of new renewable energy has become a hot spot in the field of energy. Because of the environmental protection, economic advantages, and widely distribution, the ocean tidal energy has become the emphases attention energy. Vertical-axis Tidal Turbine is one of the ocean tidal energy conversion devices. At present, this type of turbine is not widely applied because of the low energy conversion efficiency and the strong periodicity of energy output. Therefore, the three-blade vertical axis tidal current turbine has taken as the research object and the optimization research of the energy output stability and the capture efficiency of the tidal current turbine have conducted by targeting the aspects of fluctuation of the energy output of the turbine and installation of the duct. The main research contents are as following:1)Three kinds of "triangular" blades with distributed characteristics of 30°, 45°and 60°spiral were designed by changing the temporal position distribution of blade elements in the direction of blade height. In order to obtain the energy performance comparison between the three kinds of modified blades and the original straight blade, the numerical analysis of the flow field was carried out by using the computational fluid dynamics method when they operating normally. Taking the Cp value of energy capture coefficient as a reference coefficient in one periodicity,it's can be found that compared with the straight impeller, the mean value of Cp of "triangular" impeller has different degree of increasing and decreasing, and the fluctuation range of Cp is generally lower than straight impeller under the 5 kinds of different tip speed ratio conditions. In the "triangular"impeller, the mean and standard deviation of Cp is smaller with the blade helix angle increases, it's means that the stability of the output is improved with few cast of energy output.2)This paper presents a method for optimizing the design of the inner wall of the duct. The geometric design parameters of the inner wall of the duct was used as the optimal design variable in this method. The Darrieus turbine energy output quality parameter was taken as the objective function, and the multi-Particle swarm optimization was used as an optimized search strategy to optimize the inner wall profile of the duct. The numerical results show that the stability of the turbine energy output was improved effectively because of the optimization of the inner wall profile of the duct, and its better energy accumulation effect also promoted the output energy of the turbine.In this paper, the new "triangular" blade turbine energy output has different degrees of increasing or decreasing, and its stability of the operation is better than ordinary turbine. This is one of the structural form with potential development. The final optimization results of the duct show that the proposed method is effective. And this method can provide a reliable theoretical guidance for the design of the duct of other types of power generation devices.