Design And Optimization Of Yaw Mechanism Of Half-rotating Impeller Tidal Turbine

Tidal energy is a kind of clean energy with large reserves and high energy density.Its development and utilization cannot be separated from the development of turbine,and the turbine's power coefficient is the main index to measure the utilization rate of tidal energy.Half-rotating impeller tidal turbine(HRITT)is a new type of vertical shaft hydraulic turbine with combination of lift and drag,which has the advantages of excellent starting performance and high power coefficient.Due to the asymmetry of the movement of the HRITT,the change of the flow direction will have a great influence on its hydrodynamic performance.Therefore,This paper focuses on the design and optimization of the yaw mechanism of the HRITT,in order to ensure it can quickly face the incoming flow with the optimal inflow angle when the flow direction changes,so that it can operate stably and efficiently.The main research contents and results of this paper are as follows.Firstly,the working principle of the HRITT and the operation analysis of the HRITT under different flow directions were introduced.Through CFD numerical simulation,the hydrodynamic performance of the HRITT operating different flow deflections was analyzed,and the reliability of the numerical simulation was verified by underwater experiment,so as to determine the optimal inflow angle of the HRITT.Based on the optimal inflow angle,the hydrodynamic performance of the HRITT operating at yaw was analyzed.The results showed that when the yaw angle is greater than 30°,a higher yaw response capacity was needed.When the yaw angle is in range of-3° to 3°,it can meet the requirements of the turbine.Secondly,the yaw mechanism model of the HRITT was established,and two design schemes,the rotary arm yaw mechanism and the tail wing yaw mechanism,were proposed.On the basis of scheme comparison,it was determined that the yaw mechanism of the HRITT is the tail-wing yaw mechanism.Then,the yaw bearing and rudder installation position in the tail-wing yaw mechanism were analyzed.Thirdly,the tail type yaw mechanism of HRITT has been designed and analyzed.Three kinds of trailing-wing airfoils were proposed,which are delta tail,rectangular tail and droplet tail.On the basis of the consistent tail area,S,and aspect ratio,?,of the three tail,Fluent was used to numerically calculate the tails of the three airfoils to obtain the yaw moment.Based on the yaw moment coefficients of the three kinds of tails at the yaw angle of 30°,the characteristics of each tail were analyzed,and combined with the consideration of consumables,the shape and structure of the tail wing were further determined.Finally,in order to further improve the yaw response ability of tail type yaw mechanism of HRITT,the mechanism parameters were optimized.The yaw motion equation of the tail has been established to obtain the yaw response time.The numerical calculation of the tail wing has been established by using 6-DOF model in Fluent,and the numerical calculation results was compared with the theoretical analysis results to verify the feasibility of the theoretical analysis.The parameters of the yaw mechanism of the tail fin in the theoretical analysis model have been optimized by genetic algorithm,and the optimal structural parameters of the tail fin were obtained.