Dynamic analysis of eccentric mechanical face seals

Most current noncontacting face seal designs have either the flexibly mounted stator or flexibly mounted rotor configuration. In the former the stator is flexibly mounted to its base while the rotor is rigidly mounted to a rotating shaft, and in the latter the rotor is flexibly mounted to the shaft while the stator is fixed to its housing. Dynamic analyses have demonstrated that the flexibly mounted rotor has superior dynamic performance because of gyroscopic moments which tend to align the rotor.; This work describes a seal configuration (denoted FMRR) in which both seal elements are flexibly mounted and both are attached to rotating shafts.; The fluid film forces and moments in this configuration are obtained and used to derive linearized rotor dynamic coefficients. The equations of motion are then derived in terms of these coefficients, the properties of the flexible support, and the inertia properties of the rotors. The stability and steady-state solutions of the system are obtained, and a parametric study is performed on a reference case to demonstrate the application of the solution techniques. Conclusions about the behavior of the FMRR configuration are drawn from this study.; These results are extended to the case in which the seal elements are eccentric. Additional rotor dynamic coefficients are derived from the radial forces and from the effect of the eccentric deflections upon the tilting moments. The equations of motion for the radial deflections are included in the analysis, and the radial translations are shown to be coupled with the tilting modes.; The stability and steady-state response of the FMRR seal are shown to depend upon the ratio of the transverse and polar moments of inertia in each rotor, with short rotors providing better results. The gyroscopic moments dominate the response, with fluid coupling transmitting gyroscopic aligning moments between the rotors in cases where only one rotor is short. Corotating operation is shown to be undesirable for seals in which only one rotor is short because of the absence of these hydrodynamic moments.