为研究三维旋转下沟槽减阻机理,以NREL 5 MW风力机为研究对象,在叶片展向位置18%~20%处布置横向圆弧型沟槽,通过数值模拟方法计算不同工况下风力机叶片三维截面翼型和对应工况下二维翼型的气动性能,对截面翼型的表面压力系数与二维翼型的表面压力系数以及流场流动状态进行对比。结果表明,截面翼型布置圆弧型沟槽在一定风速范围内可改善截面翼型的压力分布,有效抑制流动分离,提高翼型升阻比;而二维翼型布置圆弧型沟槽对流动分离的抑制并不明显。通过二维沟槽和三维沟槽内流动状态对比,发现截面槽内三维旋转效应是沟槽减阻的根本原因。翼型失速前,沟槽内的漩涡将高速流体带出并注入边界层中,使得沟槽后方的流速变快,翼型失速后沟槽内的漩涡捕获了低能量流体,两者均改善了截面翼型的压力分布。
Abstract
To investigate the drag reduction mechanism of grooves under three-dimensional rotation, the NREL 5 MW wind turbine is taken as the research object, and transverse arc-shaped grooves are arranged at 18%-20% spanwise position on the blade. The aerodynamic performance of the three-dimensional sectional airfoil and the corresponding two-dimensional airfoil under different operating conditions are calculated using numerical simulation methods. The surface pressure coefficients of the section airfoil are compared with those of the two-dimensional airfoil, and the flow field status is analyzed. The results show that the arc-shaped grooves on the section airfoil can improve the pressure distribution of the airfoil and effectively suppress flow separation within a certain range of wind speeds, thereby increasing the lift-to-drag ratio. However, the suppression of flow separation by the arc-shaped grooves on the two-dimensional airfoil is not significant. By comparing the flow status inside the two-dimensional grooves and three-dimensional grooves, it is found that the three-dimensional rotational effect inside the grooves is the fundamental reason for drag reduction. Before stall, the vortices inside the grooves carry high-speed fluid out and inject it into the boundary layer, resulting in accelerated flow velocity behind the grooves. After stall, the vortices inside the grooves capture low-energy fluid, both of which improve the pressure distribution of the section airfoil.
关键词
风力机 /
旋转流动 /
减阻 /
数值模拟 /
气动性能
Key words
wind turbines /
rotation flow /
drag reduction /
numerical simulation /
aerodynamic performance
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