CFD-Predicted on Rotordynamic Characteristics for Labyrinth Seal Under Gas-Liquid Two-Phase Conditions

Abstract

In this study, computational fluid dynamics (CFD) was integrated with dynamic mesh technology and user-defined functions (UDFs), and the whirling motion equation was derived in detail. A numerical simulation investigation was conducted on the rotordynamic characteristics of labyrinth seals under gas-liquid two-phase conditions. The reliability of the numerical model was verified by experimental measurements of leakage flow rate, and the results showed that the variation trends of the two were consistent with a maximum relative error of 22.3%, indicating a good applicability of the model. The effects of three pressure drops, three rotor speeds and three different gas volume fractions (GVF) on the frequency-independent and frequency-dependent rotordynamic coefficients (including direct stiffness, cross-coupling stiffness, damping coefficients and effective coefficients) were analyzed systematically. The results demonstrated that an increase in pressure drop enhanced the direct stiffness and direct damping, while a rise in GVF led to a reduction in these coefficients; an increase in rotor speed improved the direct stiffness but decreased the direct damping, and exacerbated the negative effect of cross-coupling damping. The effective stiffness (K_eff) exhibited a parabolic variation trend with the whirling frequency, whereas the effective damping (C_eff ) remained positive over the entire frequency range, which ensures the operational stability. This study provides a theoretical basis for the design and optimization of labyrinth seals in two-phase flow environments, and is conducive to improving the operational stability of industrial rotor systems.