The Static Instability Characteristics of Labyrinth Seals: Experiments and Computational Fluid Dynamics Verification

Abstract

The paper proposed an experimental measurement to identify the fluid-induced force and static stiffness coefficients. A three-dimensional fluid model of the labyrinth seals was also established. And the static characteristics under different eccentricities and inlet pressure were studied. Theoretical results show a good agreement with the experiment results. The labyrinth seal with different eccentricity ratios produces a de-centered fluid-induced force and a negative direct static stiffness, which cause the rotor deviating from the geometric center of the stator. Both the fluid-induced force and negative direct static stiffness coefficient with a value of −13.5 kN/m to −72 kN/m increase with increasing eccentricity and inlet pressure. Particularly, the direct static stiffness coefficient shows a relatively significant increase with a high eccentricity ratio (∼>40%). The static instability is mainly due to the fact that the fluid velocity in the small clearance increases more rapidly along the leakage path. The inertial force is increased significantly and the pressure decreases. This results in a greater pressure distribution in the larger clearance. The fluid force and direct static stiffness coefficient that tend to push the rotor away from the stator center are produced, and eventually lead to the static instability of the labyrinth seal.