Numerical prediction of rotordynamic coefficients for an annular-type plain-gas seal using 3D CFD analysis

Abstract

Annular-type gas seals in many types of compressors and turbines are designed to reduce leakage and enhance the vibrational stability of the turbo machinery. Many researchers have attempted precise theoretical evaluation of the leakage and the rotordynamic coefficients from reaction forces of small seal gaps. The Bulk-flow model, which is based on Hirs' lubrication equation, is a general method with advantages of simplicity and short computing time. However, due to the disadvantage of the long time required to develop analysis code, and constraints from complicated seal shapes, CFD analysis is currently preferred. In the present, the method for determining the rotordynamic coefficients of an annular plain-gas seal, which is the simplest shape of gas seals, is suggested by extending the analysis of an annular plain-pump seal. A relative coordinate system for steady-state simulation is defined to calculate the compressible flow field and dynamic pressure distribution of the seal gap. The present analysis is verified by comparison with results acquired from Bulk-flow analysis code and published experimental results. The 3D CFD rotordynamic coefficients results of direct stiffness(K) and cross coupled stiffness(k) show better improvements in prediction.