Research On The Dynamic Response Of Wind Turbine Blades Under Strong Wind

The length of the blades of in-service wind turbines is relatively large.When the blades are subjected to strong wind loads,they are prone to fatigue damage.This brings new challenges to the maintenance and repair of the blades,which seriously affects the normal operation of the wind turbines and reduces work efficiency.Herein,1.5 MW horizontal axis wind turbine blades are taken as the research object.Based on the aeroelastic response principle of wind turbine blades,the fluid-structure coupling numerical calculation method is used to explore the dynamic characteristics of the blades under strong wind conditions.At the same time,the aeroelastic stability of the blade under the start-stop variable conditions is calculated,and the blade failure damage assessment is carried out.Based on the research conclusions of this subject,it is possible to predict the areas where wind turbine blades are most susceptible to failure and the frequency of failures,effectively guide UAV(Unmanned Aerial Vehicle)inspections to key areas,replace the cumbersome way of detecting blades with hanging baskets,and improve inspection efficiency.The main research contents are as follows:(1)UDF(User-Defined-Function)is used to apply the wind speed distribution characteristics of the measured wind field to CFD(Computational Fluid Dynamics)numerical simulation,using unsteady calculation to simulate blade aerodynamic load distribution,and solving blade stress based on fluid-structure coupling.The maximum stress of the blade is at an azimuth angle of 30°,and the section of the spanwise layering section is r/R=0.10,r/R=0.28,r/R=0.53,r/R = 0.88 and the stress concentration section r/R= 0.10,r/R = 0.60,there is a stress peak,r/R= 0.60,the chord direction of the section x/C =0.30,there is a maximum stress of 20.6 Mpa.Analyzing the force of the blade under strong wind has important guiding significance for the analysis of the failure position and failure mode in the whole life cycle.(2)According to the blade damage posture image at the end of service,the frequency of damage caused by stress in each area of the blade is counted.The frequency of gel coat cracking in the blade tip and the middle were 77.78% and 22.22%,respectively,and no gel coat cracking appeared in blade roots.The cracks appeared 43 times,3 times and 1 times in the root,middle and tip of the blade,respectively,and the frequency of occurrence was87.75%,10.20% and 2.05%,respectively.Among the types of damage in each area,the tip of the blade is mainly caused by gel coat cracking,and the root of the blade is mainly caused by cracks.There are two types of failure in the leaves with low frequency.Comparing the stress distribution law,the actual damage position of the blade is mostly near the stress concentration area calculated by the numerical simulation,and the damage failure mode can confirm the force characteristics of the blade.(3)In view of the failure phenomenon of the blade during the start and stop process,the aeroelastic stability of the blade is explored.The maximum displacement and stress of the blade during startup are 0.70 m and 22.86 Mpa,respectively,which are 7.14 % and16.27 % larger than the displacement and stress without angular acceleration,respectively.The maximum displacement and stress of the blade during parking are 1.23 m and 32.61 Mpa,respectively,which are 37.71 % and 26.96 % larger than the displacement and stress without angular acceleration,respectively.Angular acceleration has a more significant impact on higher-order frequencies,and the frequency change of parking conditions is greater than that of starting conditions.The maximum stress of the blade under extreme low temperature is 1.75 times of the allowable stress,and the maximum deformation is1.18 times of the specified value.According to various strength criteria,the failure of the blade is determined.(4)Blade root chord folds and surface cracks,blade fatigue cracks,blade tip varnish cracking and surface scratches are the most injury modes.Low temperature has a great influence on the stress of the trailing edge of the blade,the position of the maximum chord length and the position of the root circle,causing cracks and damage to the blade,thereby reducing the service life of the blade and reducing the power generation efficiency of the wind turbine generator set.