水平轴风力机尾流湍流结构的时空演化

基于小波变换的分析方法,结合致动线模型和大涡模拟研究了一台33 kW水平轴风力机尾流湍流结构的时空演化过程.研究发现,随着距风轮平面距离的增大,尾流中各测点的平均速度先减小后逐渐增大,速度波动的幅值呈减小趋势;风轮后7倍直径内,速度曲线具有明显的周期性,反映出脱落涡通过频率为1.80 Hz,其为风轮旋转频率的两倍.风轮后1倍直径测点处的叶尖涡所在的频率为0.78~25.00 Hz,形成的涡管通过该测点的时间约为0.32 s,涡管直径约为1.83 m;3倍直径测点处出现了0.15~0.78 Hz的低频率湍流结构;7倍直径测点处叶尖涡的频率为1.56~25.00 Hz,相比7倍直径测点之前的叶尖涡频率范围有大幅减小;8倍直径测点处,与近尾流区域相似的叶尖涡的涡管形状消失;9倍直径测点处叶尖涡基本完全耗散.

Spatiotemporal evolution of turbulence structure in wake ofhorizontal-axis wind turbine

Based on the analysis method of wavelet transformation and incorporated with actuating line model and large eddy simulation, the spatiotemporal evolution of the turbulence structure of wake of a 33 kW horizontal-axis wind turbine was investigated. It was found by the investigation that with the increase of the distance from the rotor rotation plane, the average velocity of wake at each measurement point would decrease first and then gradually increase, the amplitude of the velocity fluctuation would exhibit a decreasing trend; within the region of 7 times of rotor diameter behind the wind turbine, the flow velocity curve would have a pronounced periodicity, reflecting that the passing frequency of the shed vortex was 1.8 Hz, twice as high as the rotation frequency of the wind turbine. The frequency of appearance of blade tip vortices at the measuring point of unit rotor diameter behind the rotor would be from 0.78 to 25.00 Hz, the passing time of the formed vortex tube over the measurement point would be approximately 0.32 s, and the diameter of the vortex tube would be approximately 1.83 m. A low-frequency turbulence structure with frequency from 0.15 to 0.78 Hz would appear at the measuring point of 3-fold rotor diameter from the rotor; the frequency range of blade tip vortex at measuring point of 7-fold rotor diameter from the rotor would be from 1.56 to 25.00 Hz, which was greatly reduced when compared with the case of foregoing blade tip vortex. At the measurement point of 8-fold rotor diameter from the rotor, the vortex tube shape of blade tip vortex similar to that in near wake region would disappear; the blade tip vortex at the measuring point of 9-fold rotor dimeter from the rotor would dissipate almost completely.