Research On Aerodynamic Performance Analysis And Optimization Of Offshore Helical Vertical Axis Wind Turbines Based On CFD

As a kind of renewable and clean energy,wind energy has attracted worldwide attention since the energy crisis.And vertical axis wind turbine(VAWT)has been widely used due to its good aerodynamic performance,lower start-up wind speed and lower noise.But there are also some shortcomings such as strong cyclic fatigue force on the blades and unsmooth power output,which not only lowers the wind power coefficient but reduces the lifetime of wind turbines.More and more efforts have been invested in developing VAWT,but the research on the VAWT is still at an early stage.The dynamic numerical simulation for straight blade VAWT was completed with computational fluid dynamics(CFD)to study the aerodynamic load characteristics and verify reliability.The paper proposed helical vertical axis wind turbines on the basis of straight blade VAWT.The paper calculated aerodynamic load of helical VAWT and analyzed the effect of helical twist angle,tip speed ratio,solidity,pitch angle and height-diameter ratio on the aerodynamic performance of VAWT to seek out the optimal structural parameters.The investigation showed that compared to straight blade VAWT,the helical VAWT could reduce the volatility of instantaneous torque coefficient and improved the power coefficient effectively.The paper applied a combination of CFD and Taguchi method to optimize the aerodynamic performance of helical VAWT.Tip speed ratio,chord length,pitch angle and height-diameter ratio were implemented as the design parameters and the Taguchi method was applied to find out the optimal combination of the selected factors.The optimal combination was chord length of 80mm,a pitch angle of-4~o,height-diameter ratio of 1.2 as well as tip speed ratio of 2.5.The power output of the optimized wind turbine is found to increase by 20.15%in comparison to the baseline model.The present paper used moving mesh method and user define function(UDF)to investigate the aerodynamics of an OF-VAWT(offshore floating VAWT)in periodic surge or pitch motion.The investigation showed that the heave motion made little difference on the aerodynamic performance of VAWT,but the surge and pitch motion could widen the variation ranges of the aerodynamics forces.And the differences between the maximum and minimum of the rotor’s torque forces increased with the growth of the surging or pitching amplitudes and with the decrease of periods.In addition,the surge or pitch motion could reduce the power output of the VAWT.