考虑粗糙度敏感位置的钝尾缘翼型气动性能研究

针对考虑粗糙度敏感位置的风力机翼型钝尾缘改型前后的气动性能进行研究,揭示钝尾缘改型对表面粗糙翼型增升效果的影响规律。基于k-ωSST湍流模型,计算表面光滑与粗糙的S822翼型的升、阻力系数,并与试验结果进行比较;采用坐标旋转变换与缩放横纵坐标系数相结合的方法,建立钝尾缘改型型线数学表达式,分析对称钝尾缘改型増升效果得到S822翼型的最佳尾缘厚度;研究吸力面和压力面布置粗糙度时翼型的气动性能,获得上、下翼面的粗糙度敏感位置;对具有粗糙度敏感位置的翼型按最佳尾缘厚度进行钝尾缘改型,计算改型前后翼型的升、阻力系数和升阻比,并分析尖、钝尾缘翼型的粗糙度敏感性。结果表明:翼型进行钝尾缘改型的最佳尾缘厚度为2%弦长;吸力面和压力面的粗糙度敏感位置分别为距前缘1%弦长和5%弦长处;钝尾缘改型使升力系数和最大升阻比均明显升高,显著改善了表面粗糙翼型的气动性能,且尖、钝尾缘翼型的粗糙度敏感性综合指标值为10.68%和8.15%,降低了翼型对粗糙度位置的敏感性。研究结论可为表面粗糙风力机叶片翼型的设计和优化提供指导。

Aerodynamic performance of blunt trailing-edge airfoil considering roughness sensitivity position

Wind turbine is often exposed to dramatically different operational conditions, from icy environments to deserts with sand storms, and there are contaminants in these environments, like dust, dirt, ice, and even insects. These contaminants change the aerodynamic shape of blade and increase the surface roughness, which results in the lower utilization rate of wind energy. The aerodynamic performance of wind turbine blade can be improved through the airfoil modification, so the blunt trailing-edge structure is adopted during the design of an airfoil. Compared with the original airfoil, the blunt trailing-edge modification with bigger trailing-edge thickness and cross-section area not only has a great improvement in the maximum lift coefficient and the stall angle of attack, but also makes the maximum lift less sensitive to the leading-edge roughness. Therefore, it is of great significance to study the aerodynamic performance of blunt trailing-edge modification of the airfoil with rough surface for the improvement of the power utilization coefficient of wind turbine. The aerodynamic performance of the airfoil with rough surface and the blunt trailing-edge modification have been numerically and experimentally investigated in recent years. However, these 2 problems have been discussed separately, and the effects of the blunt trailing-edge modification on the aerodynamic performance improvement of wind turbine airfoil have been less investigated considering the roughness sensitivity position. In the present study, the aerodynamic performance of wind turbine airfoil and its blunt trailing-edge modification considering the roughness sensitivity position was numerically investigated to reveal the effect of the blunt trailing-edge modification on the lift enhancement of airfoil with rough surface. The dedicated wind turbine airfoil S822 from National Renewable Energy Laboratory (NREL) was used for the simulation. The lift and drag coefficients of S822 airfoil with smooth or rough surfaces were calculated by thek-ω SST turbulence model, and were compared with the aerodynamic data from wind tunnel tests, which offered a good opportunity to examine the capability of CFD (computational fluid dynamics) simulation. The mathematical expression of the blunt trailing-edge airfoil profile was established using the coordinates' rotation combined with the zoom coefficient of coordinates, and the airfoil S822 was modified to be symmetrical blunt trailing-edge airfoil. The lift enhancement of modified airfoils was analyzed to get the best trailing-edge thickness. In order to obtain the roughness sensitivity position of suction and pressure surfaces, the aerodynamic performance of the airfoil with rough surface was studied. The lift and drag coefficients and the lift-drag ratio were calculated for the airfoils with the roughness sensitivity position and their symmetrical modifications with the best trailing-edge thickness. Andthe roughness sensitivity of sharp and blunt trailing-edge airfoils was also analyzed. The results indicated that the best trailing-edge thickness was 2% of chord length for symmetrical blunt trailing-edge airfoil. The roughness sensitivity positions of suction and pressure surfaces were 1% and 5% of chord length away from the leading-edge, respectively. After the blunt trailing-edge modification, the lift coefficient and the maximum lift-drag ratio of the airfoil with the roughness sensitivity position significantly increased. The lift-drag ratio of the blunt trailing-edge airfoil was higher than that of the original airfoil for the angle of attack less than 11.19° when the suction surface of airfoil is rough, and so does the airfoil with rough suction and pressure surfaces. It is the same change ruler as above for the airfoil with rough pressure surface at different angles of attack ranging from 1° to 13.23°. The blunt trailing-edge modification makes the lift coefficient and the maximum lift-drag ratio significantly increase, which remarkably improves the aerodynamic performance of rough airfoil. The compositive index of the roughness sensitivity was 10.68% and 8.15% for sharp and blunt trailing-edge airfoils, respectively. The modification reduces the airfoil's sensitivity to the roughness position. The research provides a significant guidance for designing and optimizing the wind turbine airfoil under rough blade surface conditions.