Nonsynchronous
Instability of Centrifugal Compressors
J. C. Wachel, ASME Paper 75-PET-22, 1975 .
The increased
use of flexible shaft centrifugal compressors has resulted in an
increase in instability vibration problems, particularly in high
pressure applications where the aerodynamic effects are significant.
Nonsynchronous instability vibrations can occur in any machine unless
careful consideration is given to all the factors that cause this
type of vibration problem. This paper discusses these factors and
presents actual field instability vibration data obtained in three
case histories. Data analysis and presentation techniques are described
which allow a better understanding of the characteristics of nonsynchronous
instabilities. Using the instrumentation and techniques described
in this paper, the onset of instability of a machine can sometimes
be anticipated and remedial action taken before unbounded vibrations
occur. The documentation of instability characteristics for several
machine modifications, including bearing span, bearing type, seals,
impellers, etc., shows that present analytical techniques are not
adequate to predict the observed phenomena.
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