Rotordynamic Coefficients and Leakage Analysis of Labyrinth Seals in Oil-Free Centrifugal Compressor Using Transient CFD Approach With Refrigerants

Abstract The growing demand for efficient and reliable oil free centrifugal compressors in applications such as data center cooling and heat pumps has necessitated advancements in seal design and analysis. Labyrinth seals play a crucial role in ensuring compressor efficiency and rotor stability by minimizing leakage and influencing rotor behavior. This study examines the performance and rotordynamic characteristics of two labyrinth seal configurations — Tooth-on-Stator (TOS) and Tooth-on-Rotor (TOR) — operating with refrigerants R134a and R1234ze. The analysis focuses on for coefficients including effective damping, which are critical for understanding rotor stability. Three prediction methods are employed and compared: the Bulk Flow Method (BFM), steady CFD with rotating reference frame and transient CFD for multiple frequencies. The transient CFD method incorporates a multiple frequency whirling model and mesh deformation techniques to capture the dynamic interactions between gases and rotors. This method is believed to provide more accurate predictions compared to BFM and steady CFD, which are limited in their ability to represent the complexity in seal analysis. The results highlight significant discrepancies among the methods. Transient CFD emerges as the best method in calculating force coefficients of seals when running with refrigerants. The study finds that the TOR seal consistently outperforms the TOS seal in terms of effective damping, providing better rotor stability under the current labyrinth seal design and compressor working conditions. This research underscores the need for advanced computational methods in seal analysis to accurately predict performance in modern high speed centrifugal compressors. The finding offers valuable insights into the seal rotordynamic stability, guiding the optimization of labyrinth seal designs. By addressing these challenges, this study contributes to the development of more efficient and reliable compressors, which are essential for reducing energy consumption and supporting global sustainability goals.