Study On Oscillation And Hydrodynamic Coefficients Of Vertical Axis Tidal Current Turbine

With the traditional fossil energy drying up and the environment problem increasing,tidal current energy,as a type of clean renewable energy without pollution provides new vitality to energy structure.Tidal current turbine is the core component part of the tidal current energy conversion devices,which attracts attention from all over the world.The advantages of the floating tidal current power station with vertical axis turbine are simple support structure and good adaptability of vertical tidal current turbine to the different flow directions.However,in the real ocean environment,the wave has influenced the 6-DOF motion of the turbine which would result in the period variation of the relative velocity and the change of the hydrodynamic performance of the turbine.In the present,the research on the vertical current turbine mainly focuses on the hydrodamic performance of the turbine rotating with fixed axis,and barely referes to the six-degree freedom motion,therefore,the hydrodynamic performance of the turbine with oscillation and its hydrodynamic coefficients are studied in this paper.Firstly,in order to discuss the hydrodynamic performance of the floating vertical axis tidal current turbine in wave,the calculation model of the tidal current turbine with single degree of freedom oscillation in the uniform flow was built.The oscillation and the rotation of the turbine were simulated by CFD dynamic model;the effect of the oscillation on the hydrodynamic loads and the hydrodynamic performance of the turbine were analyzed.Secondly,the calculation model of the hydrodynamic coefficients of the vertical axis turbine was set up.CFD calculation results were fitted,and the hydrodynamic coefficients of the turbine in stopping station and working station were obtained.Finally,numerical simulations on the three-dimensional tidal current turbine were carried out;the three-dimensional effect on the hydrodynamic performance of turbine was studied,and hydrodynamic performances of turbine under different ratio between the span and radius were discussed.The research results show that: when turbine is oscillating,the average values of the turbine loads keep unchanged,while the transience loads are obviously fluctuating;The relations that the loads have to the tip-speed,the blade numbers,and the solidity of turbine under the oscillation are the same to that without the oscillation;The fluctuation amplitudes of loads are linearly increasing to the frequency and amplitude of the oscillation.The added mass force of the turbine is so small that it can be ignored;The damping coefficients of the working turbine is a periodic function to the azimuth angle of the turbine,which is obviously affected by the speed ratio,the blade number and the solidity,but not related to the oscillation amplitude,the oscillation frequency,and the phase difference between oscillation and rotation.The research results are significant to the research on the hydrodynamic performance of the vertical axis turbine in the real ocean environment,and they would be used to perfect the frequency domain motion response equation of the tidal current power station.