Research Papers: Design Theory and Methodology

Stability of an Axial Thrust Self-Balancing System

[+] Author and Article Information
Takashi Shimura

e-mail: shimura.takashi@jaxa.jp

Satoshi Kawasaki

e-mail: kawasaki.satoshi@jaxa.jp

Masaharu Uchiumi

e-mail: uchiumi.masaharu@jaxa.jp

Toshiya Kimura

e-mail: kimura.toshiya@jaxa.jp
Japan Aerospace Exploration Agency,
1 Koganezawa,
Kakuda, Miyagi, 981-1525, Japan

Mitsuaki Hayashi

IHI Corporation,
1 Nakahara,
Isogo, Yokohama, Kanagawa, 235-8501,
Japan e-mail: mitsuaki_hayashi@ihi.co.jp

Jun Matsui

Yokohama National University,
79-5 Tokiwadai,
Hodogaya, Yokohama, Kanagawa,
240-8501, Japan
e-mail: jmat@ynu.ac.jp

Manuscript received August 10, 2012; final manuscript received December 5, 2012; published online January 18, 2013. Assoc. Editor: Frank C. Visser.

J. Fluids Eng 135(1), 011105 (Jan 18, 2013) (7 pages) Paper No: FE-12-1381; doi: 10.1115/1.4023197 History: Received August 10, 2012; Revised December 05, 2012

Rocket pumps are characterized by high speed and high delivery pressure. Therefore, balancing of axial thrust acting on the rotor assembly is one of the most important factors. To realize complete axial thrust balancing, a balance piston-type axial-thrust self-balancing system is often used in rocket pumps. This axial thrust balance system acts dynamically as if it were a mass and spring system, although there is no mechanical spring. Sometimes, large amplitude axial vibration is observed in a liquid hydrogen turbopump. Too much vibration in the axial direction causes metal-to-metal rubbing, resulting in fatal accidents of rocket turbopumps. However, the cause of the vibration has not yet been clarified. In the present study, the self-balancing system was modeled by combining the mechanical structure and the fluid system in a calculation program of one-dimensional multidomain system analysis software. Stability of the system was investigated using this program and the possibility of existence of self-excited vibration was confirmed. Effects of geometry, fluids, viscous damping, radial pressure drop in the chamber, and orifice flow coefficients on the stability of the balance piston system were examined. As a result, it was concluded that large compressibility of liquid hydrogen was the cause of the large amplitude axial vibrations. With the results of analyses, methods to stabilize the system in order to suppress the axial vibration were suggested.

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Fig. 8

Effects of the viscous damping of the balance piston

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Fig. 5

Step response of the LH2 case for large viscous damping

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Fig. 4

Steady characteristics of the balance piston

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Fig. 2

Schematic of the balance piston

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Fig. 1

Internal flow system of the turbopump

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Fig. 9

Effects of the volume behind the balance chamber

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Fig. 7

Step response of hypothetical incompressible LH2 case

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Fig. 6

Step response of the LH2 case for small viscous damping

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Fig. 10

Effects of the variable volume of the balance chamber (the volume was changed by the chamber axial clearance)

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Fig. 11

Effects of the downstream impedance

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Fig. 12

Effects of the total axial clearance of the orifices

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Fig. 13

Effects of the radial pressure drop in the balance chamber

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Fig. 14

(a) Effects of the flow coefficients of the inlet orifices, and (b) effects of the flow coefficients of the outlet orifices

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Fig. 15

Mode shape of the system under unstable conditions

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Fig. 16

Mode shape of the system under stable conditions




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