Rotordynamics of a Mechanical Face Seal Riding on a Flexible Shaft

Abstract

A mechanical face seal is a triboelement intended to minimize leakage between a rotating shaft and a housing, while allowing the shaft to rotate as freely as possible. All dynamic analysis to date have concentrated on the seal itself. In reality, however, especially in high speed turbomachinery, shafts are made flexible and the dynamics of seals must be coupled with the dynamics of shafts. (Perhaps the dynamics of other triboelements, such as gears, bearings, etc., have to be included as well.) In this work the complex extended transfer matrix method is established to solve for the steady state response of a noncontacting flexibly mounted rotor mechanical face seal that rides on a flexible shaft. This method offers a complete dynamic analysis of a seal tribosystem, including effects of shaft inertia and slenderness, fluid film, secondary seal, flexibly mounted rotating element, and axial offset of the rotor center of mass. The results are then compared to those obtained from an analysis that implicitly assumed the shaft rigid. The comparison shows that shaft dynamics can greatly affect the seal performance even at relatively low speeds.