Study On High Cycle Fatigue Life And Prevention Of Axial-flow Turbine Blades

With the development of the economy and the tightening of environmental resources,turbomachinery has developed toward high parameters and large-scale.The size of blades has continuously increased and the working environment has become more stringent.This imposes higher requirements on the service life of blade design.In the design stage,the strength,vibration,fatigue parameters and stress state of the blade are obtained.This not only improves the product quality,ensures the reliable and safe operation of the blade for a long period of time,but also obtains more economic benefits.An accurate and reasonable predicted life span not only satisfies the reliability requirements for turbomachinery design,but also guides its design,maintenance,and monitoring.The main work of this thesis is as follows:(1)The application of several finite element methods in impeller strength and vibration is introduced.Based on this,taking the turbine blades as an example,the steps and results of finite element analysis and the safety assessment of blade vibration are introduced in detail.The analysis method provides reference for the static strength calculation and vibration safety design of the blade at the design stage.(2)Based on the crack failure of axial-flow wind turbine blades used in a mine in China,the paper proposes the calculation flow of blade dynamic stress calculation under airflow excitation force.By calculating the data of aerodynamic damping,aerodynamic force,dynamic stress,and fatigue safety factor at different blade angles,the damage of the blade in the field was integrated and the cause of cracks in the blade was found.Several methods to prevent fatigue failure of the blade were also presented.(3)The finite element analysis method was used to study the vibration characteristics of different leaf blade cracks,and the change of blade frequency and vibration characteristics caused by the change of crack length was discussed.The modal test of the actual cracked blade was performed and the man-made test was performed.The method of manufacturing cracks was tested at different crack lengths,and the frequency and response of the blades were obtained.(4)To verify the versatile blade vibration monitoring and measurement system developed by our group,we designed a blade high-cycle fatigue test bench,introduced the structure of the experimental bench and the vibration characteristics of the experimental impeller,and laid the foundation for subsequent experiments to lay the theoretical data.In this paper,based on the blade crack failure cases as the research background,a number of different finite element simulations,numerical analysis and experimental research methods were used to study the vibration and strength of axial flow blades.In terms of blade static strength calculation and vibration safety evaluation,the calculation process and evaluation method proposed in this paper can provide reference for manufacturers;in the calculation of blade dynamic stress,this paper adopts the most advanced calculation method,combined with the actual crack fault cases,given A series of analysis results have solved practical problems.In the aspect of vibration characteristics of cracked blades,the actual cracked blades were tested by modal analysis,the influence of cracks on blade characteristics was studied,and the cracked blades were investigated from the perspective of finite element simulation.In-depth research;In the experimental platform construction,this article designed a new type of impeller that can meet different experimental requirements.The above research content can provide help and data reference for the construction of the blade health monitoring experimental platform.At the same time,it helps to improve the design quality of the axial blades of the turbomachinery and provide reliable protection for its safe operation.