| In order to increase power generation and reduce manufacturing costs,wind turbines for low wind speed adopt a technical solution of tall and slender towers and long and slender blades.Flexible design can easily cause vortex induced vibration problems.Vortex induced vibration is a fluid structure interaction phenomenon.Seriously affecting the operational safety and reliability of wind turbines.There is an urgent need to conduct research on wind turbines for low wind speed.Using engineering algorithms and numerical simulation methods,analyze the vortex induced vibration characteristics of tall and slender towers and long and slender blades.This study was funded by the Science and Technology Project "Basic Energy Technology Research Special Project(HNKJ20-H88)" at the headquarters of Huaneng Group.The research content and results are as follows:1.Systematically revealed the vortex induced vibration load characteristics and fatigue damage distribution of wind turbine tall and slender tower.Taking a 140 meter tall and slender tower as the research object.Using the effective correlation length method and spectral model method recommended by the European Union standard EN 1991 1-4,vortex induced vibration load calculation and strength evaluation are carried out.The inherent modal properties of the tower were obtained based on finite element modeling.According to fatigue stress life S-N curve,Rayleigh distribution of wind speed and Miner rule,the fatigue stress range and damage rule of tower are deduced.The critical wind speed distribution and weld fatigue damage distribution of two types of aircraft models,slender tower and rigid tower,were compared and analyzed.The calculation results indicate that the slender tower is more likely to excite second-order vortex induced vibration.The second-order vortex induced load significantly increases.It exhibits a non-linear distribution.The maximum value appears in the middle of the tower,exceeding 2×104 kNm horizontal.Annual average wind speed,wind shear,turbulence intensity,Strouhal number,damping and other parameters have a greater impact on the fatigue damage of slender tower structures.At a design wind speed of 6.5 m/s,the fatigue damage at 45%to 85%of the tower height exceeds the 20 year damage limit of 0.1 specified in the IEC 61400-6 standard for tower and foundation design.There is a risk of fatigue failure,and resistance measures or optimized structural design must be considered.2.A criterion and verification analysis method for determining the critical wind speed of vortex induced vibration of long and slender blades in wind turbines have been proposed.Based on CFD numerical simulation of the flow field,the vortex shedding characteristics of two types of airfoils with sharp and blunt trailing edges at all angles of attack were analyzed.It was found that the vortex shedding frequency of the airfoil exhibits a "J" shaped trend with increasing attack angle.Maintain a low level in areas with high angles of attack.However,the frequency of vortex shedding on the trailing edge side of a blunt trailing edge airfoil will decrease again when the incoming flow blows towards the trailing edge,increasing the risk of vortex vibration again.The Strouhal number of vortex shedding in airfoil flow field presents three linear change laws after the correction of characteristic chord length considering the angle of attack.In the high Reynolds number region,the variation is small,approximately 0.12.Based on the finite element modal analysis of blades,a criterion for determining the critical wind speed of blade vortex induced vibration was established.Taking a 93 meter long and slender blade that experienced significant vibration at a certain site as an example.A method for checking and analyzing blade vortex induced vibration has been proposed.The measured data validation show that the blade vibration displacement calculated by this method is close to the accident displacement of the on-site unit. |
