Analysis and experimental verification on the leakage of labyrinth seals under multiple factors

As the main form of shaft seal, labyrinth seals provide several advantages, such as simple structure, convenient disassembly and assembly, and the ability to withstand high pressure and other harsh working conditions. They are widely used in centrifugal compressors, aeroengines, expansion turbines, and other rotating machinery. The diversity of labyrinth seal structures and the complexity of real working conditions make its internal gas flow and heat transfer very complex. The current literature reveals several factors that affect the leakage of labyrinth seals; however, comprehensive studies on the leakage characteristics of the multifactor coupling effect have been scarce. To improve the sealing performance of the labyrinth seal and reach the development trend of modern rotating machinery, performing detailed research on the structure optimization of labyrinth seals from multiple angles is crucial.

In this study, the flow field of the labyrinth seal was simulated by FLUENT software, the influences of geometric parameters and tooth structure of the labyrinth seal on leakage were analyzed by computational fluid dynamics (CFD). The labyrinth seal experimental system was established, which could realize the labyrinth seal experimental conditions under a maximum speed of 10 000 r/min and a gas supply pressure of 0.6 MPa.

The experimental results exhibited that in the operating parameters, the pressure difference had a significant impact on the leakage, while the speed basically had no impact on the leakage. Moreover, comparison of the experimental results with the mathematical model showed that the maximum error between the mathematical model and the experimental results was 3%. The orthogonal experiment results indicated that the geometric parameters of the four tooth profiles had different degrees of influence on the leakage. Thus, the seal clearance had a remarkable effect on the leakage, while the duty cycle, depth width ratio, and tooth pitch had little effect on the leakage. After analyzing the tooth shape parameters, it was found that in the tooth shape structure, the inclined teeth had smaller leakage and reducing the inclination angle between the front teeth and the rear teeth would be beneficial to reducing the leakage. Analysis of the number of sealing teeth revealed that increasing the number of teeth was conducive to reducing the leakage without increasing the axial length. Moreover, this phenomenon was more obvious with increasing pressure difference. Therefore, when the total pressure difference was a constant value, the impact of the increasing number of teeth on the leakage rate would not change significantly.

In this study, the CFD model of the labyrinth seal is established by FLUENT software, and the internal flow field distribution and leakage characteristics of the labyrinth seal are revealed. Two geometric mechanism parameter definitions, namely, duty cycle and depth width ratio, are proposed. The parameter definition can effectively eliminate the coupling effect between the parameters, such as tooth height and tooth thickness, and provide an important reference for parameter optimization design. A sealing experimental system that can realize the working conditions of high speed and large pressure difference is generated and can monitor the leakage in real time. Moreover, the impacts of the working condition parameters, geometric parameters, number of seal teeth, and structural parameters on the leakage of the labyrinth seal are studied by the CFD model. This study is of great importance for the structural design of labyrinth seals.