Numerical Investigation of the Leakage and Rotordynamic Characteristic for a Short Staggered Labyrinth Seal

Short staggered labyrinth seals are widely used in high pressure cylinder shroud seals of steam turbines. They are good at restricting the leakage flow but do not respond well to rotordynamics and often lead to turbomachine instabilities. A numerical investigation into the leakage and rotordynamic characteristics of a short staggered labyrinth seal is carried out in this paper, concerning effects of pressure ratio, inlet preswirl, rotational speed, seal clearance and whirling frequency, using both the whirling rotor method and the multiple frequencies transient simulation method. The numerical model is verified by experimental data. The result shows that the staggered labyrinth seals have a similar but not identical leakage and rotordynamic performance compared with that of teeth-on-stator see-through labyrinth seals. The cross-coupled stiffness can be reduced by decrease inlet swirl with considering the factor of rotational speed, which can significantly benefit the stability of rotor system.