Study On Static-Dynamic Strength And Aerodynamic Load For The Multi-Impeller Rotor System Of A Centrifugal Compressor

The rotor system is the key component of the centrifugal compressor, its performance is crucial for the whole compressor operation safety. The strength check and reliability calculation of the rotor system has been becoming more and more important for the design of a centrifugal compressor. But traditionally, the attention of the designers was focused only on the centrifugal load calculation of the rotor system, while aerodynamic load was neglected. With the development of chemical industry, the inlet flow of the centrifugal compressor increases rapidly. Hence, the fluctuation of the pneumatic load acting on the rotor system increase greatly that results in fatigue damage of the rotor and decreases its life. Therefore, it is important to consider effect of pneumatic load stemming from air flow in impellers on the rotor.Based on the background of the973Project for the large scale air separation equipment, this paper investigates the performance of the rotor system for a centrifugal compressor by means of finite element method and CFD simulation, which is subjected to the centrifugal and pneumatic loads. The static-dynamic strength has been analyzed for the key parts of the rotor system. The gas flow patterns in the impellers also have been obtained, the influence of the aerodynamic load on the rotor system during the work progress has been gotten too. The contents of this paper are described as follows:By virtue of the large finite element analysis software ANSYS, the static strength and dynamic strength characteristics of the un-shrouded and shrouded impellers are analyzed, respectively, and two kinds of blade dynamic strength analysis are obtained, as well as the first six natural frequencies of the un-shrouded and shrouded impellers. The results demonstrate that the dynamic strength of the blades is more reasonable and has a high reliability for both the un-shrouded and shrouded impellers. While the natural frequency of the impeller is relatively low, this can result in frequency multiplication resonance when the frequency of exciting force is high. Therefore, it is suggested that the number of guide vanes is modified to change the frequency of exciting force, or the natural frequency of the impeller is changed so that the escape rate of the exciting frequency and the natural frequency is beyond15%to avoid the frequency multiplication resonance of the impeller.Secondly, the flow field of the un-shrouded and shrouded impellers are respectively simulated and predicted with the help of CFD software. The stress, deformation and the distribution of the flow field of the un-shrouded and shrouded impellers are respectively calculated in different work conditions, which provide the load data for the dynamic characteristics of the whole rotor system in the next chapter. Three load cases of the blade are discussed, respectively, i.e., the blade subjected to only aerodynamic load, the blade subjected to only centrifugal load, and the blade subjected to both the aerodynamic load and the centrifugal load. The calculation results show that the blade stress distribution and overall deformation trend are similar in the three cases. For the shrouded impeller, the boundary pressure of internal flow field increases with the increase of gas mass flow rate when the rotational peed is constant; while the boundary pressure of internal flow field is almost no change with the rotational speed of the impeller when the gas mass flow rate is constant. In addition, the boundary pressure of internal flow field increases gradually and regularly from entrance to exit.Thirdly, the modal analysis is carried out on the spindle of low pressure rotor system, and the first six natural frequencies are calculated. The aerodynamic load simulation and analysis are conducted for the rotor system under different working conditions. The stress and deformation characteristics of the rotor system are analyzed under different aerodynamic load conditions, and the influence of aerodynamic load on rotor system is investigated. The results show that the aerodynamic load has smaller influence on the spindle deformation of the rotor system compared with that of the centrifugal load. This fact demonstrates that the damage of the spindle or bearing stemming from the aerodynamic load is fatigue damage resulting from it alternating effect.