Predicted effects of shunt injection on the rotordynamics of gas labyrinth seals

A recent CFD perturbation model for turbomachinery seal rotordynamics was extended for labyrinth shunt injection with an arbitrarily high pressure gas. A large number of, measured cases with labyrinth injection pressure at approximately 13.8 bars (200 psi) were computed and compared with measurements. The drastically reduced (negative) cross-coupled stiffness, which is the primary advantage from the use of shunt injection in gas labyrinth seal applications, was well predicted. The agreement with measurements for k, C, and C-eff was within about 40% 60% and 10%, respectively. In addition it was found that moving the injection toward the high pressure end of the seal gives k, C and C-eff values that are rotordynamically only slightly more stabilizing. Further, the radial distributions of the flow perturbation quantities give support to the two-control volume approach for developing bulk flow models for labyrinth seal rotordynamics.