Dynamic Strain Detection And Damage Identification Of Steam Turbinerotor Blades Based On FBG

With the widely application of the steam turbine and other large rotating machinery, it is playing a more and more important role in national economy. Its security service has become the focus of many scholars' study.As the core component of steam turbine,the blade is responsible for converting steam heat energy into mechanical energy.because of the bad working condition,the rotor blade becomes a frequent failure component. Relevant statistics show that 40% of the steam turbine faults caused by blade faults,60% to 80% of blade faults is caused by vibration. Blade vibration would lead to prodigious strain. So,it is of great significance that realizing the dynamic strain monitoring of the blade to ensure the safe operation of steam turbine.The purpose of this study is to realize the dynamic strain detection of the steam turbine rotor blade, as well as to the damage identification of a blade. Choosing the 12 level rotor blade of a certain type steam turbine as the research object. Starting with the simplified mathematical model to analyse the mechanical vibration characteristic. And then,getting the stress and strain distribution regularity of the blade. Then using large-scale finite element analysis software ANSYS Workbench for the precise three-dimensional rotor blade model's simulation analysis,which is established by SolidWorks. After this,we can obtain the vibration mode of intact and damaged blades, and also the corresponding vibration frequency. In addition,we can get the strain distribution law of the blade in the condition of different rotation speed, which is under the joint action of rotating centrifugal force, gravity and air resistance. The conclusion is in comparison and validation with the theoretical analysis. According to the strain distribution to arrange the number and location of measuring points: eight measuring points on the back surface of the blade,where has larger strain. Finally,by using fiber Bragg grating sensing technology, we set up the steam turbine rotor blade distributed dynamic strain testing experiment system based on FBG. At the same time,we built a electric experiment system for comparison,using the resistance strain gauge as sensing element. Otherwise, we used the photoelectric reflex speed sensor to the real-time detection of speed. The signals of speed and FBG are collected synchronously. The dynamic strain changes of the blade at different speed conditions is successfully measured, and also the static and dynamic frequency of the blade. And the frequency error was less than 1% compare to electric strain gauge measurement results. Finally,the blade was damaged artificially, the changes of strain and static frequency and dynamic frequency of the blade were measured in the condition of same speed. The result was that the static and dynamic frequency of the damaged blade was brought down, and the strain amplitude near the damaged position increased notly. This was consistent with the results of simulated analysis,and standing for successful identification of the damaged blade. Thus,the dynamic monitoring and damage identification of the steam turbine rotor blade were realized.