Experimental Study On The Flow Field Around A Blade Under The Yaw Condition Of Fluid-Structure Coupling

In nature,the wind direction is changeable,so the wind turbine often operates in the yaw state.As the most critical component of the wind turbine,the blade is subjected to different alternating loads,and the blade deforms,which will cause the change of the flow field around the blade,aggravate the complexity of the flow field around the blade and near the wake,and seriously affect the aerodynamic performance of the wind turbine.For yaw wind turbine blades and the flow field under the condition of deformation as a result of the interaction between impact blade flow field around a problem,based on the research to develop as airfoil rated power of 300 W,1.4 m diameter of three horizontal axis wind turbine blade as the research object,in different yaw Angle and wind speed,under different working condition of tip speed ratio,The PIV experiment and two-way fluid-structure coupling numerical simulation were carried out to find the internal relationship between the flow field around the wall and blade deformation under yaw condition.Finally,the characteristic variation rule of the flow field around the blade under yaw condition was obtained based on fluid-structure coupling.The relevant research conclusions provide data support for numerical calculation of fluid-structure coupling and theoretical reference for the design of wind turbine blades.The specific conclusions are as follows.The PIV experiment of near wall flow field of wind turbine blade under yaw condition obtains the transient flow field information,and studies the flow characteristics by five characteristic quantities of velocity,kinetic energy,turbulent kinetic energy,pulsating velocity and reynolds stress.It is found that: along the blade spanwise,the axial average velocity increases gradually,and the blade tip position increases rapidly;with the increase of yaw angles,the axial average velocity increases rapidly,and the blade tip position increases rapidly The results show that the change of axial average velocity is small at the relative radius of 0.71 r/R～0.8 r/R from 5° to 15° of yaw angles,while the change of axial average velocity is obvious after 15 ° of yaw angle,increasing by 49.3%,38.6%,66.8% and55.2% respectively;compared with the same relative radius,the axial average velocity increases and decreases with the increase of wind speed and tip speed ratio.The variation of average kinetic energy is consistent with the axial average velocity,and also increases gradually along the blade spanwise direction;the relative radius along the blade spanwise direction is 0.71 r/R～1.07 r/R,and the average kinetic energy increases by 15.5%,17.5%and 15.3% compared with other yaw angles in the yaw range of 5° to 15° respectively,and increases by 49.3% at the tip speed ratio of 6.The turbulent kinetic energy,the axial pulsating velocity and the axial reynolds stress decrease at first and then increase.The turbulent kinetic energy is the smallest at the relative radius of 0.875 r/R,the axial pulsating velocity is the smallest at the relative radius of 0.85 r/R,and the axial reynolds stress is between 0.8 r/R and 0.85 r/R range is the smallest,and with the increase of yaw angles,the three changes are more obvious;with the increase of wind speeds and tip speeds ratio,compared with the same relative radius position,the three increase and decrease respectively,which shows that the flow field around the blade near the wall changes unsteadily and the disturbance is severe,which affects the lift drag characteristics of the blade.Based on the numerical simulation of flow field characteristics of wind turbine blade under the condition of fluid structure coupling yaw,the maximum deformation of the blade under the rated wind speed of 10 m/s and the rated tip speed ratio of 5.5 at six yaw angles(5°,10°,15°,20°,25° and 30°)are 18.22 mm,18.35 mm,18.36 mm,18.33 mm,18.35 mm and 18.33 mm,respectively.With the increase of wind speed and tip speed ratio,the maximum deformation of blade increases and decreases correspondingly,and the influence of wind speed on the maximum deformation of blade is greater than that of yaw angles and tip speed ratio.The results show that the deformation and stress-strain on the three blades are non-uniform,and the non-uniformity increases with the increase of yaw angles.With the increase of yaw angles,the maximum stress-strain concentration area of blade root decreases,and the stress-strain of blade trailing edge decreases;with the increase of wind speeds and tip speeds ratio,the stress-strain increases.The axial velocity increases gradually along the spanwise direction of the blade,and the increase range of the tip position is larger than that of the root.With the increase of yaw angles,the effect on tip vorticity is greater than that on center vorticity.The turbulent kinetic energy first decreases and then increases,and the minimum is at the relative radius of 0.6 r/R when the yaw angles is 5° to 25° and the relative radius of 0.7 r/R when the yaw angle is 30° compared with the position with the same relative radius,the turbulent kinetic energy increases and decreases with the increase of wind speed and tip speed ratio,which is consistent with the above PIV Experimental results,and can provide an accurate numerical simulation method for the follow-up study of the influence of different blade deformation on the flow field.