Fluid Instability

  • N. F. Rieger
Part of the International Centre for Mechanical Sciences book series (CISM, volume 273)


Fluid-film instability may occur in high speed rotating machinery whose rotor-bearing system includes fluid-film journal bearings. This instability is independent of rotor unbalance. It occurs as a self-excited whirl motion above a certain threshold speed, and is induced by the action of hydrodynamic forces within the journal bearings. The rotor journals then whirl in a circular or elliptical orbit within the bearing clearance, about the steady-state equilibrium position. The speed beyond which the shaft becomes unstable and the whirl orbit begins to increase in diameter with time is defined as the threshold speed. Fluid-film instability is strongly influenced by the type of bearings which support the rotor, and by the relative flexibility of the rotor itself.


Critical Speed Journal Bearing Fluid Film Flexible Rotor Threshold Speed 
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© Springer-Verlag Wien 1984

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  • N. F. Rieger

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