Numerical Techniques for Computing Rotordynamic Properties of Mechanical Gas Face Seals

The gas film stiffness and damping properties for a spiral grooved mechanical face seal in a flexibly mounted stator configuration are computed using the step jump method and a novel direct numerical frequency response method. The seal model has three degrees of freedom, including axial displacement of the stator and two stator tilts about mutually perpendicular diametral axes. Results from both methods agree well with previously published results computed using the perturbation method, but the two new methods have the advantage of employing computer programs used in the direct numerical simulation of motion. Based on the linearized analysis, the two angular modes are proven to be coupled together and decoupled from the axial mode. Anomalies in the gas film properties tend to occur at large compressibility numbers. The step jump method requires less computing time than the direct frequency response method but at a sacrifice in accuracy at high excitation frequencies.