| Centrifugal compressors are widely used in the petrochemical industry. It has to reduce pressure and keep the system safe in such devices, Thus the balance disc is mounted. In order to improve system efficiency, non-contact seal been installed in Interstages and balance disc. Labyrinth seal is one of the seals that has been widely used in turbomachinery. Labyrinth seals has simple structure, high stability and it needn't to touch the shaft. The leakage of the seal has a significant impact on the efficiency of the compressor, especially when the gas flow past the cavity. Airflow caused by the sealing force threatening the stability and security. Therefore, Research on Labyrinth seals leakage and stability for centrifugal compressor can improve its performance and optimize the structure. This paper is an important topic and worthy of study.Firstly, this paper analyzes the throttle mechanism of the labyrinth seal. Labyrinth seal has cavity expansion effect and gap throttling effect at work. Then the causes of the seal gas power be analyzed. At last, the formula of Sealing force been extracted.This paper based on labyrinth seals from the centrifugal compressor and established Labyrinth seals three-dimensional model. Then choosed Standard k-? model and SIMPLEC algorithm to calculate Labyrinth Seal flow field. By compared the results with the empirical formula and Bluk flow program, the accuracy of the model was verified. Expansion effect and throttle gap produced the vortex that made the kinetic and thermal energy conversion, thus Labyrinth seals reached Seal.Based on the flow field analysis, The labyrinth seals of Straight, rectangular grooves and circular grooves were compared. Studies have shown that Both the pressure ratio, and the increasing of the seal gap will reduce the sealing of the seal. The increasing of speed and the rate of pre-swirl leakage will increase leakage slightly. Groove structures broken the continuity of the wall and formed a small vortex which increased the kinetic energy dissipation and improved seal efficiency. Circular grooves was better than rectangular grooves.Sealing gas power have a great influence on the system security and stability. Based on the results of the flow field, Dynamic Characteristics and stability were discussed under different conditions. By using a rotating coordinate system simulation shaft whirl and using a small perturbation hypothesis, The damping and stiffness solved. The results show that increased the pressure ratio and the rate of pre-swirl would reduce the system stability a lot. The negative pre-swirl rate could increase stability. Expanding the seal gap could improve stability.Aming at the main factor pre-swirl ratio that affecting the dynamic characteristics and stability. Calculated and analyzed the impact of the labyrinth seal. The results show: Anti-rotation means reduced the flow area and velocity in the circumferential direction, thus the leakage is reduced a little and the rate in the circumferential direction reduced a lot. The cross stiffness reduced a lot and direct damping increased fastly. It Improved stability effective.By using the rotor dynamics software Samcef, establishing a simplified seal bearing rotor model. Analyzed the structure that containing sealing and anti-rotation device on the system and obtained Critical Speed. Then calculate the stability Index named Logarithmic decrement. The results show:containing a labyrinth seal and anti-rotation device would increase the critical speed of the system. Engineering design should avoid Critical speed range. When the rotor speed reaches 10500r/min, the labyrinth seal system logarithmic decrement would less than 0.1. At this time, system was unstable. Install anti-rotation means could improve the logarithmic decrement of the system and avoid instability. |
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