Pocket damper seals (PDSs) have been shown to offer an improved rotordynamic performance compared to conventional labyrinth seals, providing large amounts of direct damping and small cross-coupled coefficients. To this date, the rotordynamic characteristics of the PDSs have been determined using linearized models, with validity limited to small displacements of the rotor. The present investigation determines the effect of the nonlinear forces arising from the pocket damper seal on the response and stability of a PDS-rotor system when subjected to large dynamic excitations. It is determined that the nonlinear forces maintain bounded amplitudes of vibration (“limit cycles”) after the rotor passes the threshold speed of instability predicted by the linear theory. It is also found that the critical speed of the PDS-rotor system is well predicted by using both linear and nonlinear models of the seal forces, as both predictions compare well with the experimental measurements.

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