| Shaft-disk-blades system is the basic structure of turbine machinery,which has a wide application in engineering.The system rotates in a high-speed during work,suffering enormous centrifugal loads and aerodynamic force.It also suffers from high temperature,high pressure and other harsh environments which is extremely vulnerable to be damaged.With the development of the design for modern rotating machinery,when study a high-speed rotating system,the blade,disk and shaft are not considered separately,but to establish a dynamic model which can reflect the coupling vibration relationship among them.Bearing and casing systems are one of the indispensable structures of rotating machinery.They provide support for the rotor and also affect the dynamic characteristics of the rotor.In addition,there are often detuning factors in blade-disc-shaft system.This means the distribution of vibration energy in each part is different,resulting in the phenomenon of vibration localization.In this paper,the vibration characteristics of the blade-disc-shaft coupling system of a low-pressure compressor from a certain gas turbine are studied.The modal characteristics of the coupling system in the static and rotating states are studied.The dynamic model of coupled system considering support stiffness and blade-disc detuning characteristics is established,and the influence of support stiffness and detuning factors on the dynamic characteristics of the system is studied.The specific work carried out in this paper is as follows:Firstly,the domestic and foreign research on the vibration of turbine machinery is summarized.The common methods of modeling the coupling system and dynamic analysis of compressor rotor are analyzed.Vibration theory,finite element method and rotor dynamic theory are introduced in detail.The vibration equations of tuned and mistuned structures are derived.Then,the dynamic characteristics of the blade-disc-shaft system are analyzed.A finite element model considering the coupling vibration between the components of the rotor is established,and the modal characteristics of the structure under static condition and centrifugal loads caused by rotating are analyzed.The diameter vibration and coupled vibration of the system are observed.The stress distribution and resonance of the rotor structure under the rotation state are obtained.After that,the influence of support stiffness on the dynamic characteristics of the rotor is analyzed.The formula of the radial stiffness of a common roller bearing structures considering the thickness of lubricating oil slick is derived.The casing model of the rotor support structure is constructed.The casing's static support stiffness and the dynamic support stiffness under the cyclic excitation of the rotor are calculated using the finite element method.A rotor coupling model with support stiffness is constructed,and the effect of support stiffness on the natural frequency of the rotor system is analyzed.The vibration mode dominated by the shaft which is sensitive to support stiffness structure is extracted.Considering the static and dynamic stiffness,the critical speed of the rotor structure is calculated,and the Campbell diagram is drawn to analyze the resonance characteristics of the structure.It is found that the critical speed of the rotor considering the dynamic support stiffness is higher than that considering the static stiffness to some extent.Finally,the finite element models of the tuning blade-disc-shaft system and three different degrees of mistuning systems are established.The modal characteristics of the tuning system and the detuning system are analyzed,and the blade tips' displacement distribution curves of each mode are plotted.It is found that the obvious vibration localization phenomenon occurs in detuning system.Vibration is no more distributed along the rotating axis,but concentrated in one or several sectors.In addition,the resonance frequency range of the detuning system expands and frequencies separation occurs. |
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