Abstract: This paper analyzed the mechanism of blade tip losses, and derived the blade chord formula according to PRANDTL and GLAUERT blade tip loss correction factor and blade element-momentum theory. With the blade chord formula, an analytical expression of torque coefficient associated with tip speed ratio and airfoil lift drag ratio of wind turbines was deduced by integrating along the wingspan using the blade element-momentum theory, and highest torque coefficient value of wind turbines in any steady state was obtained, which might be used for pre-estimating torque coefficient of actual wind turbines in design. The research shows, the impacts of blade tip losses to chord concentrated in the blade tip area, blade tip loss will reduce the torque coefficient about 4 to 10 percent when tip speed ratio changes from 10 to 4, and the value of the loss has minimal changes with lift drag ratio.

Key words: wind energy utilization, wind turbine, torque coefficient, blade tip loss, blade element-momentum theory

摘要： 分析了叶尖损失机理，根据PRANDTL 和GLAUERT叶尖损失修正因子及叶素-动量理论，推导出考虑叶尖损失的叶片弦长公式，然后沿叶片展向积分，推导出与风力机尖速比和翼型升阻比关联的风力机转矩系数解析表达式，并得到风力机在任何稳定运行状态转矩系数的最高参数值，可作为风力机转矩系数的设计参考值。研究表明，叶尖损失对弦长的影响集中在叶尖部位，当升阻比为无穷大且尖速比从常见范围10变化到4时，叶尖损失导致转矩性能损失约4%~10%，且损失的数值随升阻比的变化极小。

关键词: 风能利用, 风力机, 转矩系数, 叶尖损失, 叶素-动量理论