Study On Technology Of Adjusting Natural Frequency Of Turbine-blade Based On FEM

The frequency of turbine blade is a vital indicator of working efficiency and the safeoperation of steam turbine set. It needs to adjust the blade natural frequency by grinding theprofile of blade which is out of the frequency tolerance. The traditional way to finding theright area of profile is often low efficiency, and the thickness of cast grinding is inaccurate.It has become an urgently needed resolve technical problems to quickly locate the rightarea of profile and determine the exact volume. Based on vibration testing techniques, finiteelement methods and sensitivity analysis techniques, this paper studied the testing method offrequency of static blades, finite element modeling and model updating technology ofbending-torsion blade with variable sections. A solution has been proposed with respect toquickly locate the right area of profile and determine the exact volume. Also associatedsoftware has been developed for engineering application.Adjusting the blade natural frequency is used to depend on the result of blade vibrationtesting. With the actual blade vibration test program, in this paper, the precautions in theprocess of blade vibration testing have been described. Suggestions are given to ensure theaccuracy of testing results.In view of finite element modeling of bending-torsion blade with variable sections, adetailed comparative analysis of the effects of different types of elements on FEM calculationresults has been conducted in this paper. The basis for selecting the shape, size and order ofFEM elements has been provided. Based on reverse modeling, taking the material propertiesof the modulus of elasticity as design variables, the finite element model of the blade has beenmodel updated. Then based on the finite difference method, a method is presented to calculatethe sensitivity of blade frequency in this paper. This method can analyze the dynamiccharacteristics of blade structure under the influence of grinding which laid the foundationfor adjusting the blade natural frequency.Finally, associated software has been developed for engineering application in MatlabGUI environment. With the actual operating requirement, it provides a complete solution foradjusting the blade natural frequency. At present, it has been applied in actual productionprocess with the company’s approval.