Research On Hydrodynamic Performance Of Vertical Axis Tidal Turbine With Controlable Pitch

Tidal current energy is an important part of marine renewable energy.It has the characteristics of large energy density,good predictability,good stability and abundant reserves.Vertical axis tidal current turbine is an important mechanism to obtain tidal current energy.In order to obtain higher mechanical efficiency,the use of pitch form is an effective method.Therefore,the theoretical and experimental research on the performance of pitch turbine has important scientific significance and economic value for the development and utilization of tidal current.This topic comes from Heilongjiang Province Natural Science Fund "Vertical axis turbine pitch regulation optimization" and the State Key Laboratory of Marine Engineering(Shanghai Jiaotong University)open project "Pitch tidal current turbine experimental study".In this paper,the working principle and force characteristics of vertical axis pitch turbine are introduced firstly.The computational fluid dynamics software CFX is applied to two-dimensional numerical simulation method.The feasibility and accuracy of the numerical simulation are verified by three typical examples.Then,the numerical simulation method is used to study the difference between the load and performance of the pitch control turbine and the turbine with zero installation angle.It is found that the pitch turbine can effectively enhance the blade tangential force without increasing the resultant force of the blade,which can not only reduce the overall impeller load but also effectively reduce the fluctuation of the blade and impeller load.The main reason for the analysis is that the pitch turbine reduces the variation range of the geometric attack angle of the blade,thus slowing the flow separation of the blade to a certain extent and maintaining the lift,thus improving the performance of the turbine.Then,a model of power loss calculation for control pitch vertical axis turbine is proposed.The relationship between loss power and blade declination law and angle of attack is analyzed by two examples.It is found that the variation of power loss and blade declination amplitude is positively correlated,and the phase angle range corresponding to the pitch power loss will have a big difference due to the difference of the turbine model parameters and the tip speed ratio.There is a certain phase difference between the peak of the power loss and the peak of the angle of attack.Finally,through the model experiment,the experimental data and numerical simulation results are compared.Taking into account the complexity of the experimental environment,the error is considered to be within the acceptable range.The speed ratio,velocity and density of the active pitch turbine are also analyzed.The influence of the blade load and the impeller load was correspondingly concluded.In this paper,CFD numerical simulation and model experiment were used to study the hydrodynamic performance of the control pitch turbine.The hydrodynamic principle of the performance of the variable pitch turbine is compared with that of the fixed pitch turbine.The factors which affect the performance of its pitch turbine and their corresponding variation rules were summarized.The proposed control pitch power loss model can effectively evaluate the relationship between output power and input power of pitch turbines in practical application.The research results of this paper will provide a solid theoretical basis and practical design basis for the technical development of vertical axis turbine,which can be extended to the design and application of vertical axis wind turbine and river turbine in engineering.