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Effects of Cavitation on Rotordynamic Force Matrices

Brennen, C. E. and Franz, R. and Arndt, N. (1988) Effects of Cavitation on Rotordynamic Force Matrices. In: Proceedings of the 3rd Conference on Advanced Earth-to-Orbit Propulsion Technology, Huntsville, AL, 1988. NASA Conference Publication. No.CP-3012. NASA , Washington, DC, pp. 227-239.

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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. This paper concentrates on the fluid-induced rotordynamic forces acting upon the impeller and therefore on the bearings. Self-excited whirl, where the rotor moves away from and whirls along a trajectory eccentric to its undeflected position, can result from these fluid-induced forces. The purpose of the present work is to study the full range of these forces so that they can be included in any rotordynamic analysis at the design stage. To study the fluid-induced rotordynamic force on an impeller vibrating around its machine axis of rotation, an experiment in forced vibration was conducted. The prescribed whirl trajectory of the rotor is a circular orbit of a fixed radius. A rotating dynamometer mounted behind the rotor 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 conducted over a full range of whirl/impeller speed ratios at different flow coefficients for various turbomachines including both centrifugal impellers aand axial inducers. A destabilizing force was observed over a region of positive whirl ratio. The range of flow conditions includes an examination of the effects of cavitation on the observed rotordynamic forces.

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Additional Information:The authors are indebted to the NASA George Marshall Space Flight Center, for continued sponsorship of this research under contract NAS8-33108. The authors want to thank Dr. Acosta and Dr. Caughey for their participation in this research.
Series Name:NASA Conference Publication
Issue or Number:CP-3012
Record Number:CaltechAUTHORS:BREteopc88a
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:67
Deposited By: Christopher Brennen
Deposited On:30 Dec 2004
Last Modified:02 Oct 2019 22:16

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