| Tidal stream energy is one of the important forms of marine renewable energy,which is characterized by strong predictability,large storage capacity and easy access.At present,a critical issue in the design of horizontal-axis tidal stream turbine is to efficiently utilize bidirectional tidal stream energy.Therefore,the yaw method of a horizontal-axis wind turbine based on a tail wing is introduced into the horizontal-axis tidal stream turbine,and a horizontal-axis tidal stream power generation device capable of adaptive tracking the flow direction of tidal stream is presented in this paper.The device passively adjusts the turbine to adapt to the change in flow direction based on the hydrodynamic performance of the flat tail wing.Furthermore,it depends on the lift produced by the tail wing at a small yaw angle and the magnetic force produced by the permanent magnet to make the rotating plane of the turbine stable.Through structural design,yaw dynamic performance analysis,blade design and optimization,numerical simulation,and flume experiments,the design and the rationality of the model proposed in this paper are discussed and verified.The main works are as follows.(1)The research status of bidirectional energy acquisition of tidal stream turbines was presented,and the application of bidirectional tidal stream power generation device based on variable pitch and yaw was discussed.Furthermore,the research progress of blade optimization,numerical calculation and yaw characteristics of horizontal axis tidal stream turbines was analyzed,which provides an important theoretical basis for the design and analysis of yaw mechanism of horizontal-axis turbines.(2)The method of a horizontal-axis wind power generation device based on a tail yaw was introduced into the horizontal-axis tidal stream power generation device,and the overall structure design was carried out,including the energy acquisition and conversion device,adaptive yaw structure,support structure,where the working principle was described.The dynamic balance equation of the turbine yaw mechanism was established by using Newtonian mechanics method.The yaw conditions of the turbine before and after starting were analyzed,and the influence of the position of the yaw shaft and the gravity of the tail on the yaw performance was discussed.(3)The fundamental methods of airfoil theory,BEM theory(Blade Element Momentum),and impeller loss correction theory were investigated for the analysis and design of tidal current blades.The 3D model of the blades was constructed by utilizing the Profili and Solid Works software.The Wilson method and Nonlinear Programming Model(NLPM)were adopted to optimize the design of tidal stream turbine blades,and the performance of the turbine was predicted by the CFD method.By analyzing the hydrodynamic performance of blades with different pitch angles,taking into account the energy and thrust characteristics of the impeller,the optimal pitch angle of 3 ° was selected,with an energy acquisition coefficient of 0.335 and a thrust coefficient of around 0.7.(4)The physical model of the power generation device of the adaptive yaw horizontalaxis turbine was constructed.By analyzing the yaw moment of the turbine and the resultant moment of the yaw system,the optimal design range of the relative position of the yaw shaft and the tail gravity of the model was discussed.The test results show that when the flow velocity is lower than about 0.15 m/s,the turbine can well yaw to the corresponding angle range with the flow velocity change,and when the flow velocity is higher than about 0.15m/s,the turbine can stabilize at the expected yaw angle of about 5 °.At the same time,compared with non-magnetic assisted yaw,the output power of the model is increased by more than 4.47% in the flow velocity range of 0.15 m/s～0.31 m/s.The swing of the turbine is greatly reduced,which proves that the magnetic assisted yaw is helpful to improve the efficiency and operation reliability of the adaptive yaw turbine.The above research work shows that the yaw method based on the tail wing can drive the horizontal-axis tidal stream turbine adapt to the change of flow direction well.Among them,the position of the yaw shaft and the gravity of the tail directly affect the bidirectional power flow adaptive performance of the horizontal axis turbine.Combined with the magneticassisted yaw design,the efficiency and reliability of the device have been effectively improved.The research in this paper has a very important application value for the efficient capture and reliable operation of the bidirectional flow of the horizontal-axis turbine. |
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