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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. California Institute of Technology , Pasadena, CA. (Unpublished)

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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:Report or Paper (Technical Report)
Additional Information:Report No. 249.8 on Contract NAS 8-33108. I would like to express my gratitude to Professor A. J. Acosta for his guidance and patience during the course of this work. I would also thank Professors C. E. Brennen and T. K. Caughey for their encouragement and continued interest in this research. I would like to thank Mike Gerfen for his help in keeping the facility running. Haskell Shapiro provided assistance in wrestling with the motor control. John Lee aided in rebuilding the data taking and motor control systems. Help in making various drawings was provided by Cecilia Lin. The assistance provided by fellow residents of the lab: Norbert Arndt, Steve Ceccio, R. Scott Miskovish and Fei Zhuang is appreciated. I also want to thank the others not mentioned here for their various contributions. I gratefully acknowledge the Shell Foundation for providing a fellowship that supported my graduate studies. This research was supported by NASA George C. Marshall Space Flight Center under contract NAS 8-33108. Finally, I thank my parents and my sister for their continued encouragement during my stay at Caltech.
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Shell FoundationUNSPECIFIED
NASA George C. Marshall Space Flight CenterNAS 8-33108
Record Number:CaltechAUTHORS:20140421-134856725
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:45084
Deposited On:21 Apr 2014 22:01
Last Modified:03 Oct 2019 06:26

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