Research On The Effect Of Crack Damage On Dynamic Response Of Wind Turbine Blade

The wind power industry has grown rapidly in recent decades,with many wind turbines reaching the end of their service life.Blade is the core component of wind turbine,which runs for a long time in the harsh natural environment.Under the influence of complex alternating load,wind turbine blade is easy to cause fatigue damage,and crack is the main form of fatigue damage.If it can not be repaired in time,the cracks will continue to extend,leading to blade fracture,which will bring serious losses to the wind turbine and even the whole unit.Therefore,it is very important to study the crack damage of wind turbine blade.In this paper,the wind wheel of a 1.5MW wind turbine with crack damage is taken as the research object.The dynamic characteristics of the wind turbine with crack damage,the law of crack propagation and the failure characteristics of the damaged blade are studied by means of numerical calculation.Verifying the accuracy of calculation results by comparing with real pictures taken by UAV.The main research contents of this paper are as follows:(1)The inlet wind speed is defined as the rated wind speed of 12m/s and the strong wind speed of 19m/s,and the UDF function is compiled based on the measured wind field data.Take the shear flow as entry condition,analyze stress distribution of wind turbine blades with different types of crack damage under rated and strong wind speeds by using sliding mesh technology.it is proved that the cracks are mainly concentrated in the blade root and blade,especially the trailing edge of the blade,by comparing with pictures taken by UAV,and the laminated section area is also easy to cause the crack.Under the rated wind speed,the crack distribution at the blade root area has the maximum stress,which is33.34 Mpa.Under the strong wind speed,the crack distributed in the middle area of the blade has the largest stress,which is 44.31 Mpa.The main stress leading to crack propagation is tensile stress.The crack growth trend along the chord direction is the strongest,while the crack growth trend along the span direction is the weakest.(2)The propagation of surface cracks in both homogeneous and composite airfoil sections is analyzed.Cracks on surface of composite airfoil propagate along the length and depth directions simultaneously,while those on composite airfoil propagate along length direction only,and the stress concentration on surface crack of composite is not significant during the propagation process,which indicates that the laminated structure of composite material can prevent the crack propagation.Whether the crack length or the crack depth increases,the crack damage to the blade will be intensified.However,the deeper the crack depth is,the more fiber layers need to be destroyed for crack propagation,which will slow down the crack propagation speed to some extent.(3)It is found that the stress at crack tip is proportional to the change of crack size by analyzing the stress variation of crack size.As for the crack at blade root,if blade is to fail,the crack length shall reach 1/2 of chord length,and crack depth shall reach 1/2 of the blade thickness.For the crack at blade middle,if blade is to fail,the crack length shall reach 3/8 of chord length and the crack depth shall reach 1/3 of blade thickness.Extreme ambient temperatures,such as cold and high temperature,will increase the stress at the blade tip,significantly increase the deformation of the blade,and intensify the dynamic failure of the blade.Low temperature has a greater effect on blades.