分形尾缘叶片气动性能及流场数值模拟

针对风力机存在尾流效应问题,通过在垂直轴风力机叶片尾缘布置分形孔的方法,建立分形叶片三维实体造型,进行了分形叶片和原始叶片三维非定常不可压流动的分析,得出叶片绕流流场数值模拟结果,重点研究具有分形特征的尾缘对叶片尾流流场及叶片气动特性的影响。结果表明:分形叶片对改善叶片尾流流场有较显著作用。在8°~18°攻角范围内,分形叶片升、阻力系数随攻角变化波动性小于原始叶片;当攻角大于原始叶片失速攻角时,这种波动性差距更大。分形孔的存在使叶片周围流场结构及气动参数对攻角变化敏感性降低:在攻角大于原始叶片失速攻角时,分形叶片阻力系数随攻角变化标准差仅为原始叶片的0.6倍,升力系数标准差仅为原始叶片0.4倍。研究结果将改善垂直轴风力机叶片尾流互相干扰及水平轴风力机叶尖脱落涡情况。

Numerical Simulation of the Aerodynamic Performance and Flow Field of a Fractal Trailing Edge formed Blade

In the light of the wake flow effect existing in wind turbines, through adopting a method for arranging fractal holes at the trailing edge of blades on a vertical shaft wind turbine, a three dimensional solid entity model was established and the three dimensional unsteady uncompressible flows around a fractal blade and the original one were analyzed respectively with the numerical simulation results of the flow fields around the foregoing blades being obtained. The emphasis was placed on the investigation of the influence of the blades having fractal characteristics at the trailing edge on their wake flow fields and aerodynamic characteristics. It has been found that the fractal blade has a relatively conspicuous role in improving the wake flow field of a blade. Within a range of the attack angle from 8 degrees to 18 degrees, the fluctuation of the lift and drag coefficient of the fractal blade will be smaller than those of the original blade with changes of the attack angle. When the attack angle is bigger than the stall attack angle of the original blade, such a fluctuation will be even bigger. The presence of the fractal holes will force the sensitivity of the configuration of the flow field around the blade and the aerodynamic parameters to changes of the attack angle decline. When the attack angle is bigger than the stall attack angle of the original blade, the standard deviation of the drag coefficient of the fractal blade will be only 0.6 folds of that of the original blade and the standard deviation of the lift coefficient will be only 0.4 folds of that of the original blade when changing with the attack angle. The foregoing research results can make better the mutual interference among the wake flow of blades in a vertical shaft wind turbine and vortexes separated from the blade tips in a horizontal shaft wind turbine.