Theoretical And Experimental Study On Three-dimensional Wake Characteristics Of Horizontal-axis Wind Turbine

The existence of wind turbine wake effect leads to power loss and fatigue load increase of downwind turbine in the wake region,which further affects the safe operation of the wind turbine and the economic benefits of the wind farm.The damage caused by the wake effect can be effectively reduced through the layout optimization and coordinated control of the wind turbine based on the understanding of wake model and wake characteristics using experimental or theoretical studies.Based on this,the above two wake research methods were combined in this thesis to investigate the three-dimensional wake flow field characteristics of the horizontal-axis wind turbine,and the following three aspects are studied:First of all,to fill the gap of the current mainstream two-dimensional wake models can only predict the wake speed distribution in the horizontal plane of the wind turbine hub height,and the existing three-dimensional wake models do not consider the wind shear effect of inflow,an improved 3D Jensen-Gauss wake model with the considerations on the wind shear effect and the anisotropy of wake expansion is proposed,which is based on the classical Jensen wake model and the wind speed distribution in the wake region exhibits the characteristics of Gaussian distribution.The empirical model of turbulence intensity in wake region is adopted to modify for the wake expansion coefficient.Secondly,in order to explore the three-dimensional wake speed distribution characteristics of real wind farms and provide data support for wake model verification,the field measurement using two ground-based scanning Li DARs was conducted to detect the wake characteristics of horizontal-axis wind turbines in a wind farm located in northern Hebei Province,China.The precision calibration,main wind direction analysis,wind turbine selection,Li DAR layout,mode setting and data processing are conducted.Based on the measurement results of the wind turbine wake,the development characteristics in the horizontal plane of the single-row wind turbine hub height under four typical inflow conditions are analyzed.Results show that the interference between the single-row wind turbines is affected by the wind direction.In the cases where the incoming wind speed is basically the same,the greater the incoming turbulence intensity,the faster the wake recovery rate.In addition,the incoming wind profile and the characteristics of the wake speed distribution in vertical plane under two different incoming wind speed conditions are analyzed.The analysis shows that under certain conditions of other variables,the wind shear effect is positively correlated with the incoming wind speed,and the wake effect is not obvious when the incoming wind speed is higher than the rated wind speed of the wind turbine.Finally,the wake models are compared and verified with the experimental data of single wind turbine obtained by Li DARs,including the wake center line,the horizontal plane of the wind turbine hub height and the vertical height plane.Furthermore,the three-dimensional wake characteristics of single wind turbine are analyzed based on the experimental data and the prediction results of the wake model.Results show that:(1)the wake speed predicted by the 3D Jensen-Gauss model is highly consistent with the measured data,and also,has the highest accuracy compared with the existing wake models.The proposed 3D wake model can well predict the three-dimensional wake distribution characteristics of the single wind turbine;(2)With the increase of the downwind distance,the wind speed on the wake centerline shows a gradual recovery trend and the horizontal wake width gradually expands;(3)The distribution of wake speed in the horizontal plane of wind turbine hub height is approximately axisymmetric Gaussian distribution,and the distribution of wind speed in vertical height plane of the wake region is asymmetric due to the influence of the incoming wind shear.