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Experimental Investigation of the Effect of Cavitation on the Rotordynamic Forces on a Whirling Centrifugal Pump Impeller


Franz, Ronald John (1989) Experimental Investigation of the Effect of Cavitation on the Rotordynamic Forces on a Whirling Centrifugal Pump Impeller. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/5JXT-CZ84.


The interaction of a rotating impeller and the working fluid introduce forces on the rotor. These fluid-induced forces can cause self-excited whirl, where the rotor moves away from and whirls along a trajectory eccentric to its undeflected position. When designing a turbomachine, particularly one which is to operate at high speed, it is important to be able to predict the fluid-induced forces, both steady and unsteady, acting on the various components of the machine. The fluid-induced rotordynamic forces acting upon the impeller and therefore on the bearings was investigated for a centrifugal impeller in a spiral volute in the presence of cavitation. An experiment in forced vibration was made to study the fluid-induced rotordynamic force on an impeller whirling around its machine axis of rotation in water. The whirl trajectory of the rotor is prescribed to be a circular orbit of a fixed radius. A dynamometer mounted behind the rotor and rotating with it measures the force on the impeller. The force measured is a combination of a steady radial force due to volute asymmetries and an unsteady force due to the eccentric motion of the rotor. These measurements have been carried out over a full range of whirl/impeller speed ratios at different flow coefficients for various turbomachines. A destabilizing force was observed over a region of positive whirl ratio. Cavitation corresponding to a three percent head loss did not have a significant effect upon this destabilizing force. However, a lesser degree of cavitation at the design point for the impeller-volute combination tested increased this destabilizing force for a particular set of whirl ratios

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Cavitation; rotordynamic forces; centrifugal pump impeller
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Minor Option:Applied Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Acosta, Allan J.
Thesis Committee:
  • Acosta, Allan J. (chair)
  • Brennen, Christopher E.
  • Caughey, Thomas Kirk
  • Hunt, Melany L.
  • Zukoski, Edward E.
Defense Date:5 January 1989
Funding AgencyGrant Number
NASANAS 8-33108
Record Number:CaltechETD:etd-02022007-133417
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:467
Deposited By: Imported from ETD-db
Deposited On:20 Feb 2007
Last Modified:15 Jul 2021 18:31

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