Researchon Aerodynamic Characteristics Of Vertical Axis Wind Turbine With Eccentric Rotor Structure

With the rapid development of wind power market,the straight-bladed vertical axis wind turbine(SB-VAWT)became more and more popular because it's suitable for small and medium-sized wind power market,the SB-VAWT is still difficult to self-starting at low wind speed and its output power is still low.A rotor with eccentric structure for SB-VAWT was proposed in order to improve the self-starting capacity and output power performance,which is based on the wind turbine's own structure and avoid the complicated structure,it works by increasing the effective radius of blade aerodynamic force to rotor shaft.The concept of Eccentric amount was defined..A SB-VAWTwhose diameter is 0.6m and height is 0.5m was manufactured.And six kind of eccentric amount were set as 0,10 mm,20mm,30 mm,40mm,50 mm.Numerical simulation,mechanical analysis and wind tunnel experiment are used conjunctively in this study to analyze the effects of eccentric rotor structure on the aerodynamic performanceas follow:(1)Effect of eccentric rotor structure on self-starting capacity of wind turbine.The self-starting capacity of the two blade SB-VAWT and three blade SB-VAWT with six kind of different eccentric amount with different wind speed were tested by wind tunnel experiment;The static torque characteristics of the six kind of SB-VAWT with different eccentric amount at different azimuth angles were calculated by numerical simulation to explain the impact of the eccentric structure on the start capacity of the wind turbine;The wind turbine wind force was analyzed to explain the reasons for the static torque difference caused by the different eccentric structure and the mechanism of the eccentric structure;The influence of eccentric structure on the flow field near wind turbine is demonstrated from the view of flow field.(2)Effect of eccentric rotor structure on aerodynamic characteristics of wind turbine.The rotate speed characters of the two blade SB-VAWT and three blade SB-VAWT with six kind of different eccentric amount with different wind speed and the output power characteristics at 10 m / s wind speed were tested by wind tunnel experiment,the better performance of eccentric wind turbine and non-eccentric wind turbine were selected to further test the output power characteristics at different wind speed to verify the eccentric wind wheel structure on the wind turbine output performance improvement effectiveness and universality;The dynamic moment characteristics of the wind turbine during the operation are calculated by the numerical simulation method,and the dynamic flow field of the wind turbine with different wind turbine eccentricity was simulated.The main conclusions under the experimental conditions as follows:(1)The eccentric structure has a great influence on the starting characteristics of the wind turbine,the eccentric rotor with proper eccentric amount can remove the minus static torque coefficient at some azimuth angles and make the vibration range of torque coefficient become smooth which improve the general starting performance of SB-VAWT.But the effect of eccentricity on the static moment of the wind turbine is closely related to the azimuth angle and also has negative effects at some azimuth angles.The mechanism of its influence is mainly due to the eccentric structure of the blade aerodynamic changes in the rotation center caused by the location.Therefore,the amount of eccentricity should be appropriate,too small or too large has negative effects.(2)The eccentric structure has a great influence on the dynamic aerodynamic characteristics of the wind turbine,mainly in two aspects: For the rotate speed characters of the wind turbine,eccentric structure on the rotate speed of the wind turbine has a large degree of improvement effect whether it is for the 2-blade SB-VAWT or 3-blade SB-VAWT,the appropriate eccentric amount can make the rotate speed of SB-VAWT at low wind speed to reach even more than the higher wind speed compared to the SB-VAWT without the eccentric structure;For the wind turbine output power characteristics,the appropriate eccentricity can effectively improve the wind turbine output power coefficient at both low tip speed ratio and high tip speed ratio.In this study of six eccentric amount,the best eccentricity of the amount is while L = 30 mm,In this eccentricity,the power coefficient can increase more than18% compared to no eccentric wind turbine within the range of the experimental tip speed ratio,the power coefficient of 3 blade wind turbine reached the maximum power factor and the maximum power factor has more than 20% increasing compared to no eccentric wind turbine.(3)The eccentric wind turbine structure proposed in this study does not add any additional devices to avoid complicating the wind turbine structure,and improved the static starting characteristics,rotate speed characteristics and output power characteristics of the SB-VAWT in a certain extent,The torque ripple during the operation of the machine become smooth and the stability of the wind turbine during operation also enhanced.It shows that the performance of the wind turbine can be improved only from the optimization of the wind turbine structure,which provides a new idea for the future design and development of the wind turbine.