Oil whirl,oil whip and whirl/whip synchronization occurring in rotor systems with full-floating ring bearings |
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Authors: | Bernhard Schweizer |
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Institution: | 1.Department of Mechanical Engineering, Multibody Systems,University of Kassel,Kassel,Germany |
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Abstract: | High-speed rotors are often supported in floating ring bearings because of their good damping behavior. In contrast to conventional
hydrodynamic bearings with a single oil film, full-floating ring bearings consist of two oil films: An inner and an outer
oil film. As single oil-film bearings, full-floating ring bearings also show the typical fluid-film-induced instabilities
(self-excited vibrations). Both inner and outer oil films can become unstable and exhibit oil whirl/whip instabilities.
The paper at hand considers a Laval (Jeffcott) rotor, which is symmetrically supported in full-floating ring bearings, and
investigates the occurring oil whirl/whip effects by means of run-up simulations. It is shown that the inner oil film, which usually becomes unstable first, gives
rise to a limit-cycle oscillation with an exactly circular rotor orbit, if gravity and imbalance are neglected. Interesting
is the instability generated by the outer oil film. The calculations demonstrate that instability in the outer oil film does
not lead to a simple circular limit-cycle orbit. Whirl/whip-induced limit-cycle oscillations generated by the outer oil film are more complex and entail a coupled circumferential and
radial motion, although the mechanical problem is radially symmetric, if gravity and imbalance are neglected. Thus, whirl/whip instability in the outer fluid film may be interpreted as symmetry breaking.
Finally, a further kind of bifurcation/instability occurring in rotors supported in full-floating ring bearings—called Total Instability in this paper—is analyzed. It is shown that Total Instability is caused by synchronization of two limit cycles, namely synchronization of the inner and outer oil whirl/whip. Total Instability is of practical interest and observed in real technical rotor systems, and frequently leads to complete rotor damage. |
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Keywords: | Oil whirl Oil whip Full-floating ring bearing Self-excited vibrations Symmetry breaking Synchronization Total Instability |
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