Research On Design Method Of Secondary Turbine For Contra-Rotating Double Impeller Tidal Energy Generator

As a kind of renewable energy with abundant reserves and environmental friendliness,ocean energy has been paid more and more attention by all countries in the world.As one of the most predictable and easy-to-develop forms,tidal current has enormous scientific and economic value.Compared with the EU with rich tidal energy resources and the most advanced development technology,China's current energy resources is low.The existing technology of the EU cannot be directly used in China,which needs to make corresponding localization improvements.Considering the general single impeller tidal energy power generation device,the efficiency improvement is limited due to the existence of the rotating wake.In order to utilize the kinetic energy of the fluid in the rotating wake to improve efficiency,a double impeller tidal energy generating device can be formed by adding a secondary turbine opposite to the steering of the single impeller tidal power generating device.In this paper,a design method for the secondary turbine of the dual-impeller horizontal axis tidal current power generation device is proposed.The fluid simulation software is used to simulate the velocity field and flow development parameters of the front turbine,and the optimal spacing and the diameter of the rear turbine of the double turbine are determined.And then by averaging the unsteady flow to a constant flow,while adding the tangential velocity into the blade element theory and adding the flow development parameters to the momentum theory,the blade element momentum theory is improved to be suitable for the rear turbine design.And the design of the turbine blade is finished.Based on this method,the effectiveness of the method is proved by numerical simulation and experimental tests.The main work of this paper is as follows:(1)The velocity field after the front turbine is analyzed in the theoretical way,and this velocity field is used as the inflow condition of the rear turbine.The blade element momentum theory is improved to be suitable for the rear turbine design.And then the average method of converting the unsteady flow into a steady flow to obtain the design of the secondary turbine of the dual turbine power generation device.(2)According to the existing conditions of our laboratory,a set of contra-rotating turbine power generation devices is designed according to the proposed designmethod,and in the design process,the fluid simulation software is used to assist the simulation analysis of the flow field after the front turbine.(3)A model of the dual turbine power generation is set and simulated by using the fluid simulation software Fluent,predicting the possible of cavitation phenomenon,and proposing to reduce the risk of cavitation,and at the same time,its power and efficiency is predicted.(4)The previously designed dual turbine power generation unit was fabricated using 3D printing technology,and its performance was tested using a test sink.Through the above research work,it can be proved that the design method proposed in this paper can improve the turbine conversion efficiency of the tidal current power generation device.This design method can be used to design low-flow tidal energy turbines that meet the current trend of China's tidal energy resources.