Study On Wake Characteristics Of Horizontal Axis Wind Turbine And Its Impact On Structural Dynamic Response

With the large-scale development and effective utilization of global wind energy,the overall structure of the wind turbine is developing towards the direction of extra-large blades and super-high towers,due to the characteristics of the structure itself,such as high height,slender shape,etc.Wind load often becomes the main control load of wind turbine design,so it is very important to study the wind turbine response under wind load to ensure its safe operation.The wake effect is the main factor that affects the wind turbine layout position and the wind turbine power generation efficiency.In the actual operation of the wind field,the wind speed decreases after the wind turbine works,and the downstream wind turbine in the wake region operates in the wake,the energy output decreases,the turbulence increases,and the fatigue load on the wind turbine increases.In order to reduce the influence of wind turbine on the wake of downstream fan,increasing the distance between wind turbines is the most direct and effective method.However,due to the shortage of international energy and the large-scale establishment of wind power station,the large wind field takes up a large area,problems such as low wind flow density are also gradually emerging.Therefore,how to adjust the layout of wind farm reasonably and improve the utilization rate of wind energy resource will be an important issue to be paid attention to in the future.Based on the measured wind speed and wind direction data of the Nation Wind Technology Center and a wind farm in Northwest China,the mean wind speed and wind direction,turbulence degree,gust factor,turbulence integral scale and power spectrum of pulsating wind speed are analyzed,and considering the influence of the wake factor,in the far wake flow field under the action of wind field characteristics are analyzed in detail.Finally,on this basis,the Ansys Workbench software was used to calculate the velocity distribution of the wake field,and the consistency between different wake models and simulation results was compared and analyzed,and the structural response under the effect of the wake was obtained through the fluid-solid coupling,so as to predict the damage situation under different environmental conditions.The results show that:(1)Compared with the exponential function fitting,the logarithmic function can fit the vertical wind profile better;The downwindturbulence intensity and turbulence integral scale are obviously larger than the corresponding turbulence intensity and turbulence integral scale in cross wind direction and vertical wind direction.The empirical formulas suggested by Ishizaki and Choi can well reflect the relationship between the downwind gust factor and the turbulence intensity,and the corresponding empirical formulas are obtained by curve fitting with the measured data.(2)the downwind turbulence integral scale has a tendency to decrease with the increase of the average wind speed,while the turbulence integral scale of the vertical wind direction increases exponentially with the increase of the average wind speed;the measured longitudinal pulsating wind speed power spectrum is in good agreement with the Von Karman and the Kaimal empirical spectrum,The vertical pulsating wind speed power spectrum and the Panofsky's empirical spectrum are offset in the high frequency band,and the empirical spectrum obtained by fitting is closer to the measured spectrum.(3)The existing Jensen model,Park-Gauss model and actual engineering wakes have different wake characteristics.(4)Wake effect is very important not only for the selection and layout of wind turbine,but also for the service life of downstream wind turbine.The results show that the simulation results based on k-? turbulence model are different from the different wake theoretical models in different downwind distances,and a single theoretical model can not reflect the distribution of the whole flow field.The distribution of wind speed in the near wake region is relatively disordered,but with the increase of the downstream wind distance,the velocity profile gradually presents the top cap distribution,and the wind speed in the wake region gradually recovers to the incoming wind speed,and the closer the wind speed is to the wind wheel,the more the wind speed is formed by the blade rotation.The more obvious the fan-shaped contour is,the larger the wind speed is at the outer edge of the blade.By fluid-solid coupling,the upstream wind turbine rotation not only affects the downstream velocity distribution,but also changes with the fan spacing,the fan rotation speed and the incoming wind speed.The dynamic response of the downstream wind turbine will also vary in different degrees.