Effect Of Raked Winglets On Aerodynamic And Structural Performance Of Wind Turbine Blades

In order to overcome a series of problems caused by energy shortage and environmental pollution,countries around the world are increasing the development of wind power generation,the wind power has entered a golden period.For the higher power,wind turbines are gradually moving towards large-scale development and a number of design methods have evolved to modify the blades of small wind turbines,including the addition of winglet to the blade tip,it is more simple and efficient.In this paper,we study the impact of aerodynamic and structural performance of wind turbine blades after adding winglets to the blade tips of NREL Phase VI.Taking NREL Phase VI wind turbine blades as the research object,with small winglets toward the suction and pressure surfaces,add another set of horizontally oriented winglet as a control.Calculated and compared the performance of blades before and after adding wingletss at different wind speeds.The following conclusion is drawn: Compared with the original blades,the aerodynamic performance of the three winglets blades are improved at different wind speed.However,with the wind speed gradually increasing,the surface flow of the blades getting complicated,stall phenomenon occurs,and the effect of the winglets in increasing power is reduced.The presence of winglet can obviously increase the pressure difference between the upper and lower surface of the blade,and since the winglets act as baffles,the flow of air on the blade surface is more continuous in spreading direction,and the winglets have a significant separation effect on the wing tip vortex.Using the method of orthogonal simulation,design a 3-factor 4-level orthogonal simulation table with the twist angle,tilt angle,and length of the winglet as the main parameters,and establish 16 types of winglet blade models.Under the flow condition of 7 m/s,the influence of three parameters on the torque and thrust of the wind turbine is analyzed orthogonally to determine the optimal winglet configuration.The conclusions are as follows: the optimal level of each parameter of the winglet affecting the blade torque is 6 ° for the twist angle,30 ° for the tilt angle and 4%R for the length;the optimal level of each factor affecting the thrust is 2 ° for the twist angle,15 ° for the tilt angle and 2.5%R for the length.Due to the differences in the optimal levels of the winglet parameters for torque and thrust,the optimal configuration of the winglet at7 m/s wind speed is finally determined by the comprehensive balance method as follows: 6 ° for the twist angle,30 ° for the tilt angle,and 4%R for the length.The aerodynamic loads of the original blade and the optimal winglet blade are calculated by the one-way fluid-structure coupling method under the variable blade tip speed ratio conditions,and the structural performance of the blade is analyzed in the Workbench platform.The calculation results indicate that: the aerodynamic performance of the blade with the addition of the optimal winglet configuration is excellent,and the leading edge pressure difference is greater than the original blade under different tip speed ratios.From the structural performance,the deformation pattern of the winglet blade and the original blade are similar,all of them have waving,swinging and torsional deformation,but the structural deformation amount of the winglet blade under different blade tip speed ratios is slightly larger than that of the original blade.The vibration frequency of the winglet blade under different working conditions is smaller than the original blade,the equivalent stress is concentrated in the root to the middle part of the blade,which is the biggest stress from the root circular section to the wing section transition position,but through the strength check,the ultimate stress of the winglet blade is within the range of the allowable stress of the material,so it will not cause blade fracture.