Modal Analysis On Large Wind Turbine And Its Blade Characterized By Ice Accumulation

With the rapid development of domestic wind power business,a large number of large horizontal axis wind turbines have been started to generate electricity in China.This type of wind power generator is generally a tall and slender space structure.The blades exhibit a long span,good flexibility,and are easily deformed due to their own weight and external loads.In the plateau mountainous regions of Yunnan and Guizhou Province,due to the low temperature and high humidity climate,it is difficult for the blade to avoid ice coating.In order to prevent the ice-blade blade under the influence of airflow from vibration damage,it is necessary to understand modal parameters of the iced blade.In this paper,a large-scale wind turbine with a height of 85 m and its blades of 46.5 m in length are taken as the research object.Through finite element calculations,the modal parameters of the blade and wind turbine with and without icing are investigated.The specific work is as follows:Firstly,the 3D finite element model of wind turbine blade was established using ANSYS software to compile the APDL language.The first five-order flap-wise,the first four-order lag-wise and the first-order torsional modes of the blade were calculated and then briefly analyzed.Secondly,the modal parameters of blade with or without ice are comparative analyzed.The results show that for the natural frequency,icing can increase the mass of the blade,and then reduce the natural frequency of the blade;icing can also increase the stiffness of the blade,and then increase the natural frequency of the blade.In addition,the ice distribution pattern also has a certain degree of influence on the natural frequency of the blade.For the modal shape,different icing states including the distribution,mass,and stiffness have little effect on the flap-wise and lag-wise modal shape.Only the amplitude near the tip of the blade will be different,but the torsional modal shapes of the blade in the 30 m~46.5 m zone are apparently affected on the contrary.Finally,based on preliminarily understanding the effect of icing on the mode of blade,the mode of wind turbine with ice-free or iced blades were analyzed.The results show that the variation of mode of wind turbine,which is static and characterized by ice accumulation,is in accord with that of the blade.The change of azimuth angle of iced blades has little effect on the mode of the whole machine,but it can change the order of appearance of modal shapes of the wind turbine blade;the reduction of the blade frequency increases the probability of coupling vibration with the tower,which is not conducive to safety of wind turbine.