Research On Hydrodynamic Performance Of Half-rotating Impeller Tidal Turbine

Tidal current turbine,as the core equipment of ocean tidal energy development,plays a key role in the efficient utilization of tidal current energy.Its structural principle,power mechanism and performance optimization are the key points in the research and development of tidal current turbine.Half-rotating impeller tidal turbine(HRITT)is a new type of vertical-axis turbine based on Half-rotating mechanism(HRM),which combines impeller resistance and lift characteristics organically.It has good self-starting performance and high efficiency.In this dissertation,CFD method was used to analyze the hydrodynamic performance of the HRITT.The influencing rules of each factor were obtained,which provide a basis for the structure optimization and performance improvement of the HRITT.It is great significance to the application of semi-rotating impeller in water resources development.Firstly,the working principle and structure of HRM and semi-rotating impeller(HRI)were introduced,and the flow field analysis model of HRI was established in XFlow.According to the influencing factors of the hydrodynamic performance,a numerical experiment scheme was designed,and the flow field analysis method and data processing method were determined.Secondly,combined with the numerical experiment scheme,the effects of inflow velocity,impeller speed,impeller compactness,arm length and blade number on the efficiency of HRI were studied.It was found that the maximum efficiency of the HRI varies slightly with different inlet velocities,and the corresponding optimal speed increases with the increase of inlet velocities.When the number of blades of HRI is 2 or 3,the efficiency is higher.There is a parabolic relationship between compactness and efficiency of HRI,and the length of rotating arm follows the same rule,which can be optimized to obtain the best structural parameters.Thirdly,the flow field characteristics of the HRI were analyzed according to the variation of velocity,pressure and vorticity around the blade.Combined with hydrodynamic data,the hydrodynamic formation mechanism of HRI was analyzed,which provides a theoretical basis for the blade optimization.The hydrodynamic performance of HRI was compared with traditional vertical axis turbine.The hydrodynamic characteristics of HRI were summarized and the hydrodynamic performance was evaluated.Finally,in order to further improve the efficiency of HRITT,the structure layout of HRITT was studied.It was found that the centrifugal effect will be formed in the middle of the double impeller turbine,which can increase the pressure in the middle of the impeller and increase the driving torque of the impeller,thus improving the efficiency of the semi-rotating impeller.In addition,the influence of impeller clearance,phase and speed on double impeller turbine was studied,and the optimal layout parameters of double impeller turbine were obtained.