洁净与覆冰条件下风力发电机输出功率计算方法及现场试验验证

Calculation Method of Wind Turbine Output Power under Clean and Icing Conditions Verified by Field Tests

高海拔地区风能资源丰富,然而建设于此的风力发电机面临严重覆冰问题。覆冰会破坏叶片气动结构,造成输出功率损失,影响供电质量。了解不同工况下的风力发电机输出功率情况,有助于电力部门进行合理的电力调度。该文提出了一种适用于洁净和覆冰条件下的风力发电机输出功率计算方法。该方法以叶素动量理论为基础,同时引入二维计算流体动力学(CFD)仿真方法来计算叶素的升力与阻力系数。将计算结果与现场试验运行结果对比发现,该计算方法可以在工程应用允许的误差范围内获得风力发电机的输出功率。此外,通过比较基于该方法获得的关键气动参数在不同风速下沿叶片翼展方向的分布发现,冰层的存在会降低叶片对风能的利用率,减小叶片旋转扭矩,从而导致输出功率降低;并且随着风速的增加,覆冰所带来的负面影响更加明显。

Wind energy resources are abundant in high-altitude areas,but wind turbines built here suffer serious icing problems.The accumulated ice will destroy the original aerodynamic structure of wind turbine blades,resulting in output power loss,which has bad influences on the power supply quality.Understanding the influences of different icing cases on the output power is helpful for the power department to carry out reasonable power dispatching during icing season.Therefore,a method for calculating the output power of wind turbine under clean and icing conditions was proposed.The proposed method is based on the Blade Element Momentum(BEM)theory and this theory ignores the variation of flow field along the wind turbine blades,which could increase efficiency by reducing computation time.To improve the calculation accuracy and make the calculation results more fit the actual condition,empirical formulas were introduced to correct the axial inducing factor,the tangential inducing factor,and attack angle.Because the accumulated ice changes the original aerodynamic structure of the wind turbine blades,the 2D CFD simulation based on commercial software Fluent was introduced to obtain the lift and drag coefficients of iced blade elements.Considering the influences of wind turbine structural parameters,different coordinate systems were established to correct the relative wind velocity working on the blade rotation plan.Because the contribution of one-third length blade near tip to output power reaches 90%,the proposed calculation method ignores the contribution of blade root on output power to save the computation time.To verify the accuracy and feasibility of the calculation method,field tests of the NREL S819 type wind turbine under clean and icing conditions were carried out in Xuefeng Mountain Energy Equipment Safety National Observation and Research Station.Under the icing condition,the uniform and streamline ice was chosen as the research object.Comparing the calculated results and test measured results,it is found that:(1)When the wind velocity is less than 11 m/s under clean or icing condition,the calculation method can accurately calculate the output power of wind turbine,which is in good agreement with the test measured results.(2)When the wind velocity exceeds 11 m/s,the differences between calculated results and test measured results increase gradually,and this is because the wind speed fluctuates fast and the fluctuation range is large during the field test.The maximum relative errors between two of them under clean and icing conditions are 10%and 14.1%respectively,which meet the engineering application error requirements.Based on this method,the key aerodynamic parameters along wingspan direction under different wind velocity were calculated.Results showed that:(1)The ice on wind turbine blades will decrease the axial and tangential inducing factor,which indicates that it could reduce the rotational torque of blades.(2)Icing could reduce the tangential and normal force,and the effects of icing become more pronounced as wind velocity increases.(3)The attenuation of tangential and normal force is obvious near the blade tip,which indicates that the ice will reduce the utilization of wind energy near blade tip more easily.