| As a saving and emission reduction energy,the cost of wind energy is gradually reduced,which has a good prospect of development and utilization.In recent years,the wind turbine diameter and tower height of the wind turbine are increasing with the large capacity of the single machine,the incoming flow it bears will be more complicated.In practical operation,the wind turbine is in the atmospheric boundary layer,the influence of wind shear,low-altitude jet,turbulence and other complex flow conditions on the aerodynamic performance of the wind turbine cannot be overlooked besides the uniform flow.Some studies have found that the nacelle will not only have a certain effect on the aerodynamic performance of the wind turbine,but also interact with the near wake field of the wind turbine.Furthermore,the interference between the towertube and the blade will have a periodic effect on the force characteristics,power generation capacity and life of the wind turbine,so it is very important to study the influence of the nacelle and tower-tube on the aerodynamic characteristics of the wind turbine.Therefore,the three-dimensional modeling and structured grid division of the wind turbine are carried out,and the influence of the nacelle and tower-tube on the aerodynamic performance of the upper wind shaft wind turbine under different inflow conditions such as uniform flow,wind shear and turbulence are studied by using the method of combining theory and numerical simulation in this thesis.(1)Under the condition of uniform flow and wind shear,the influence of nacelle on the aerodynamic performance of horizontal axis wind turbine is studied.The results show that the influence of the nacelle model on the pressure coefficient of the blade surface is mainly on the suction surface,and the suction surface pressure coefficient of the nacelle model is larger.The influence of the nacelle on the blade surface flow is mainly on the cylindrical and transition section of the blade,as well as the partial wing near the blade root,but the middle and above of the blade are almost unaffected by the nacelle,and the influence of the nacelle on the blade surface flow increases with the increase of wind speed.The nacelle which makes the position of the blade surface flow separation is relatively lagging,and the two models of the wind turbine and the nacelle are obviously different in the flow state of the suction surface near the blade root.Nacelle makes the aerodynamic load increase slightly,and the increase amplitude decreases with the increase of wind speed.The influence of the nacelle on the wind turbine wake is mainly embodied in the axial and radial position,and the size of the affected area is related to the shape and size of the nacelle,taking the length and the height range of the nacelle as the reference respectively.When the blade is located at different azimuth angles,the front and rear edge of the blade and the front flow of the wind turbine will influence on the wind speed near the nacelle to varying degrees,thus affecting the flow state of the upper,lower surface and the downstream of the nacelle.(2)To explore the effects of the combined effects of nacelle and tower-tube on the aerodynamic loading of horizontal axis wind turbines under the condition of different inflow condition such as uniform wind,wind shear and turbulence.The results show that the closer to the blade root position,the stronger interference effect of the tower-tube.The influence of the tower-tube on the pressure coefficient of the blade surface is mainly manifested in the suction surface,and the tower-tube which makes the pressure coefficient of the blade surface decrease relatively.With the increase of wind speed,the response of blade surface pressure coefficient to tower shadow effect is more obvious.Wind shear is the main cause of the load change,and the su perposition effect of wind shear and tower shadow can alleviate the load fluctuation.The effect of the change of turbulence intensity on the surface pressure of the blade is not obvious,the smaller the effect is when the turbulence intensity is coupled w ith the tower effect.During a rotating period,the aerodynamic loading of the single blade with the tower model reach the minimum near the azimuth angle of 180°,the amplitude of the load fluctuation is larger than that of the no-tower model and the azimuth angle of 150° to 210° is the central area of the tower shadow.The torque and thrust fluctuation frequency of the wind turbine of the two models is three times the rotation period of the wind turbine,and the load fluctuation of the wind turbine is far less than that of the single blade.With the increase of wind speed,the aerodynamic loading of the two models gradually increase,and the load fluctuation caused by the interference of the tower increases.Due to the rotating effect of the wind turbine,i t is found that the torque and thrust of the wind turbine with the tower model show opposite asymmetry before and after the tower shadow area.Both wind shear and tower effect will cause periodic fluctuation of the load,but the proportion of the tower eff ect is larger,and the load fluctuation caused by the combination of wind shear and tower effect is not a simple linear superposition of the two.The wind shear effect will produce a n aerodynamic hysteresis effect of 2°~4°.The fluctuation of the aerodynamic load caused by the change of turbulence intensity is not obvious.When the turbulent intensity is coupled with the tower effect,the aerodynamic load of the wind turbine increases to a certain extent,that is,the wind turbine output force increases,but it also leads to the increase of the ultimate load and fatigue load such as the base and blade root,which increases the ultimate bearing capacity of the components of the wind turbine.(3)Under the above three conditions,the effect of the combined ef fect of nacelle and tower-tube on the flow field of horizontal axis wind turbine are investigated.The results show that the interference of the tower makes the position where the flow separation occurs lag behind the wind turbine model at the same wind speed.As the wind speed increases,the position of the flow separation moves forward,the area of the stall area increases gradually,and the flow separation extends further along the blade extension.In addition to the flow separation of the section near the blade root,the other parts of the blade surface under three different flow conditions are basically attached flow.The comparison shows that there is no obvious difference in blade surface flow under the circumstance of uniform inflow and uniform turbulence,while the position of blade suction surface separation is lagging behind the first two.Generally,the wind speed fluctuation will not have impact on the blade surface flow,and the wind speed change is the main cause of the blade surface flow change.At the azimuth angle of 180°,the airflow flows through the tower-tube to form the carmen vortex street.The tip vortex structure is destroyed by the tower,and the wake of the tower-tube is mixed with the tip vortex,the attachment vortex and the central vortex along the radial direction,the flow field structure is more complex than the without-tower model.With the increase of wind speed,the structure of tip vortex core is clearer,the diameter of vortex core increases,the logarithm of tip vortex sequence increases,and the distance of tip vortex diffusion increases.The blade root vortex and the attachment vortex begin to form,the area of the nacelle wake increases along the axial and radial direction,and the blade root vortex system is mixed,and the influence of the tower wake on the blade surface flow is aggravated.The comparison shows that the blade vortex intensity,the mixing degree of blade vortex system and the nacelle wake,and the position and dissipation velocity of tip vortex falling downstream are different between the two models in uniform flow,wind shear and turbulence at the 0°and 180° azimuths. |
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