向心透平叶轮振动频率的有限元分析

Vibration analysis of radial inflow impeller with finite element method

应用ANSYS有限元软件对一个小型燃气轮机向心涡轮的叶轮固有频率进行了数值分析 .基于有限元方法建立了叶轮的振动方程 ,对方程中非线性的初应力刚度矩阵与离心刚度矩阵采用了线性简化 ,应用Block -Lanzos法求解振动方程的特征值 .结果表明 ,当叶轮转速上升时 ,旋转柔化效应使叶轮的低阶振动频率 ,尤其是第 1阶弯振频率不断下降 ,到某个转速时出现“零频”现象 ,原高阶静频依次成为低阶频率 ;第 1阶振型发生变化 ,但是基频大小基本没有变化 ;整体式叶轮主要振动形式是叶轮的弯扭振动 .

Based upon the general FEA platform ANSYS,the numerical results of the modal analysis of a radial inflow turbine impeller are presented.The dynamical equation of impeller in the form of FEM is derived.The initial stress matrix and centripetal stiffness matrix are linearized.The eigenproblem of the dynamical equation is solved by means of Block-Lanzos method,so the 25 modes of the impeller are obtained.In addition,the simplified dynamical equation is founded upon the dynamical equation of spinning beam,in order to explain the major dynamic characteristics of the impeller,which are validated by numerical analysis.The results of the analysis indicate:because of spin softening,when approaching to critical rotation speed,the frequency of each mode is decreased,especially for the first bending mode it is more evident.Then after,when running over the critical rotation speed,the frequency of the first bending mode rises greatly.The major shapes of the impeller are coupled bending and torsion.