Study On Performance Of Double-decker Vertical Axis Tidal Turbine

The ocean is an energy treasure which reserves vast resources. The ocean energy is not only clean and green,but also has little impact on the ecological environment. As a kind of inexhaustible renewable green resources,human's future of energy is in the wide ocean. Tidal current turbine is the device which can convert tidal current energy to electrical power.Single-decker fixed-pitch vertical axis tidal turbine has a good adaptability to the different flow directions and because of ease of manufacture and low cost, it has attracted wide attention. Single-decker vertical axis tidal turbine has some shortcomings, such as difficulty of self-starting, heavy fluctuations of the impeller load and low efficiency at low speed, which hinders its development. Thus, the paper adds an internal layer to the traditional single-decker fixed-pitch vertical axis turbine. By applying CFD numerical simulation, the performance of this kind of double-decker vertical axis tidal turbine is studied.Based on two dimensional numerical simulations, the paper firstly calculates single vertical axis tidal turbine. Comparing with the experimental results,the numerical simulation is proved to be correct. On the basis of this, the optimum range of solidity and number of blades of single vertical axis tidal turbine are obtained. By this way the size of external impeller of double-decker vertical axis tidal turbine is determined. Then, a series of two-dimensional and three-dimensional CFD numerical simulations are carried out to analyze the influence of different parameters on turbine 's performance. The parameters conclude speed ratio, azimuth difference between I&E impeller, radius ratio between I&E impeller,chord length ratio between I&E blades, internal blade airfoil, internal blade helix angle,three-dimensional effect, span ratio between I&E blades and so on. According to CFD numerical simulation, the type can effectively improve the turbine's capable of self-starting and the efficiency at the low speed, and reduce the force fluctuations and torque fluctuations on the blades and impeller.Finally, the paper carries out one-way fluid structure interaction (FSI) simulation on double-decker vertical axis tidal turbine. The results show that the stress state of internal impeller is better than that of external impeller. Considered turbine deformation, the amount of blades deformation is much less than main axis deformation. The maximum of the whole turbine's stress occurs at the root of the main axis, strength check proves the structure is safe.As the total deformation of turbine is small,two-way FSI simulation is not necessary. All of above could provide reference to design and manufacture of double-decker vertical axis tidal turbine.